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HomeMy WebLinkAboutDrainage_and_Flooding_Report-dated_03-10-08klotzassociates March 10, 2008 Mr. Ron Bottoms City. Manager City of La Porte 604 W. Fairmont Parkway LaPorte, Texas 77571 RE: City of La Porte, Texas City -Wide Drainage Study Study Letter Report #1 Klotz Associates Project No. 0127.008.000 Dear Mr. Bottoms: 1160 Dairy Ashford, Suite 500 Houston, Texas 77079 T 281.589,7257 F 281.589.7309 houston.office@klotz.com Klotz Associates was authorized to proceed with a City -Wide Drainage Study (CWDS) for the City of La Porte on January 28, 2008. Klotz Associates is pleased to submit this letter report for the completion of Tasks 1.1 through 1.7 of Phase I as prescribed in the contracted Scope of Work. Purpose The purpose of this letter report is to identify key drainage and flooding issues that are currently adversely affecting the City. These drainage and flooding problems were identified through a process of data gathering, site visits, characterization and evaluation of existing drainage, and identification of consequent drainage and flooding problems that might be expected to occur in the future if not addressed by drainage improvements or other corrective actions. Studied Area The studied area, located completely in Harris County, Texas, is the entire City of L.a Porte (City). The City is located on the extreme east side of Harris County on the shores of Galveston Bay (see Exhibit 1). The City is bounded by the City of Deer Park on the west, State Highway 225 on the north, the community of Shore Acres and properties of the Port of Houston on the south, and is bisected by State Highway 146 in a generally north -south direction. The City's boundaries encompass approximately 19.7 square miles. The City has a mixture of residential, industrial and commercial land uses. The area between Fairmont Parkway and Spencer Highway is largely small lot residential areas while some of the areas north of Spencer Highway are typical residential lot developments and some area have large lot rural residential areas. Areas east of SH 146 include residential lot developments, commercial areas and industrial areas. Part of the Mr. Ron Bottoms March 10, 2008 Page 2 of 15 k I o t z associates city is drained by storm sewer drainage systems and part of the city is drained by open ditch or roadside ditch drainage systems. Much of the areas identified as prone to drainage or flooding conditions are older areas of the City. These older areas were constructed to older standards and usually without much consideration given to handling overland surface flows also called sheet flows. Newer areas of the City generally have better drainage facilities. The City outfalls into major watersheds including: Armand Bayou, Clear Creek, and Lower San Jacinto/Galveston Bay (see Exhibit 2). The topography of the City is generally flat and average about 24 feet above sea level (see Exhibit 3). Tidal variations can significantly affect drainage in portions of the City. The city has approximately 36.1 miles of Harris County Flood Control (HCFCD) channels, and must comply with applicable drainage requirements established by rules and regulations of the HCFCD for discharges to HCFCD ditches and channels. The City has approximately 3 miles of coast contiguous to Galveston Bay. The United States Army Corp of Engineers (USACE) has authority over navigable waters, which include coastal waters and tidally effected waterways draining to these coastal waters with coordination required with these authorities. Data Collected This primary focus of the study tasks of the CWDS addressed by this letter report is the collection and evaluation of drainage data. The following summarizes the data collection activities. GIS Data The City has also provided Klotz Associates with their GIS data related to drainage issues, including repetitive loss information, storm sewer layout, culvert data, information on severely flood -damaged homes, inlets and manhole locations, and floodplain maps. Floodplains delineated and recognized by the Federal Emergency Management Agency (FEMA) floodplains are shown in Exhibit 4. Repetitive loss data provided by the City is shown in Exhibit 5B. LiDAR (light detection and ranging technology) elevation data are also readily available from HCFCD; the elevation contours developed by Klotz Associates from these data are shown in Exhibit 3. The LiDAR data were also processed using GIS software to delineate drainage areas and sheet flow paths for the 100 flood event for various watershed areas in the City; these drainage areas and flow paths in them are shown in Exhibits 6 to 10. These data assist in understanding and describing overland flow conditions and directions. As evident from Exhibits 6 through 10, the drainage is Mr. Ron Bottoms March 10, 2008 Page 3 of 15 k I o t z associates generally from northwest to southeast toward Galveston Bay on the east and Armand Bayou and Taylor Bayou on the south. Jurisdictional wetland data were downloaded from the U.S. Fish and Wildlife Service website City Staff Input A key component of the data collection and evaluation activities was discussion with City personnel about recurring significant drainage and flooding problems in various areas of the city. Five short term drainage projects were identified by the City; information provided about these areas is documented in Appendix C. Site inspection of the drainage conditions in the City was conducted by Klotz Associates as part of the data collection process; the inspection focused upon these five key areas and subdivisions with repetitive loss properties. Klotz Associates met with knowledgeable City personnel and obtained their insights as to current and anticipated drainage and flooding problems. The City has listed five locations of short term drainage projects: Catlett Drive, the Parking Lot of Creekmont Park, Driftwood Drive, Fleetwood Drive, and the Glen Meadows. The City also has subdivisions with locations of repetitive losses. The subdivisions are: Brookglen Subdivision, Creekmont Subdivision, Glen Meadows Subdivision, Fairmont Fast Subdivision, and Fairmont West Subdivision. These short term drainage projects and subdivisions of repetitive loss properties are evaluated and reported on in this letter report. Photograph Album A photograph album provided to Klotz Associates by the City provides important information on locations and extent of flooding. The photo album provides citizen documentation of street addresses for areas with flooding problems that have occurred during severe storms. The information in this album assisted in identifying areas for the site inspection by Klotz Associates. Drainage Reports Prior drainage reports have also been collected and reviewed. The following reports and studies were reviewed: • City of La Porte Master Drainage Plan (December 1982, O'Malley & Clay, Inc.) • Master Drainage Plan and Interim Improvement Recommendations for Unil FI01-00-00 (September 1987, Landev Engineers, Inc.) Mr. Ron Bottoms March 10, 2008 Page 4 of 15 klotzassociates • Clear Creek Watershed Regional Control Plan (February 1992, Danncnbaum Engineering Co.) • Hydrologic and Hydraulic Study for Interconnect of HCFC Unit B112-02-00 to Unit B109-00-00 and HCFC Regional Detention Site Unit B512-01-00 (April 1997, Wilbur Smith Associates, Consulting Engineers and Planners) • Hydraulic Analysis for Little Cedar Bayou Watershed HCFCD Unit F216-00-00 (January 2000, Binkley & Barfield, Inc. Consulting Engineers) • Taylor Bayou Watershed Master Drainage Plan; Tax Increment Reinvestment Zone #1 (August 2003, CivilTech Engineering, Inc.) • Hydraulic Analysis for Sens Road From 300' North of Spencer HWY, to 300' North of Avenue "H" HCPID Pin Cl/102/1002/005 VOL 2 (December 2003, Binkley & Barfield, Inc. Consulting Engineers) • Driftwood Drive Drainage Study, City of La Porte Pond to Park Project (June 2004, CivilTech Engineering, Inc.) • Preliminary Analysis for F216-00-00 Linear Detention (November 2004, Binkley & Barfield, Inc. Consulting Engineers) • Drainage Report —Impact and Mitigation Analysis San Jacinto and Galveston Bay Watershed,- Proposed Fairmont Parkway Improvements From 16'h Street to state HW 146 (December 2005, TSC Engineering Company) • Hydraulic Analysis for Sens Road From 300' North of Spencer HWY. to 300' North of Avenue "H" HCPID Pin Cl/102/1002/005; Little Cedar Bayou (F216- 00-00) & HCFCD Channel A104-07-00 (February 2005, Binkley & Barfield, Inc. Consulting Engineers) • Hydrologic & Hydraulic analysis Port Crossing Development (June 2006, Goldston Engineering, Inc.) The older reports of those listed above provided only limited information; use of information from these older reports must be used with caution and possibly revised for the present CWDS. For instance, most of the reports have HECI and HEC 2 hydrologic and hydraulic models that are for the most part no Ionger used in Harris County; current modeling in Harris County uses HEC-HMS and HEC-RAS software models. A summary review of each of the reports is provided in Appendix B. Mr. Ron Bottoms March 10,2008 k10tzassociates Page 5 of 15 Record Plans Review of the drainage infrastructure data provided by the City suggests that updating of the data using City plans and as -built data will be necessary. Incomplete or unavailable as -built information may complicate the update of the drainage information. Hydraulic and Hydrologic Models Up-to-date hydrologic models (HEC-HMS) and hydraulic models (HEC-RAS) based upon information developed as a consequence of the Tropical Storm Allison Recovery Program (TSARP) are readily available from HCFCD and have been incorporated into the information for this project. The hydrologic models that were obtained are for Clear Creek Watershed, Armand Bayou Watershed, and Galveston Bay Watershed. The hydraulic models that were obtained are as followed: • Clear Creek Watershed - A 104-00-00 (Taylor Bayou) A104-07-00 (Tributary 3.93 to Taylor Bayou) • Armand Bayou Watershed - B106-00-00 (Big Island Slough) - B 109-00-00 (Spring Gully) - B 109-03-00 (B 112-02-00 Interconnect) - B 112-00-00 (Willow Springs Bayou) - B 112-02-00 (Tributary 1.78 to Willow Spring Bayou) • San Jancinto/Glaveston Bay Watershed - F216-00-00 (Little Cedar Bayou) Site Visit and Drainage Problem Evaluation Field visits of the City drainage systems were carried out to complement the study and provide an on -the -ground understanding of the drainage situation. Selected photographs taken during the site inspection are shown in Appendix A. Generally, the City drainage is dominated by a combination of runoff from small residential lot neighborhoods with lot sizes in the 0.15 to 0.25 acre range, large rural -like residential lot neighborhoods with lot sizes in the 3 to 5 acre range, and industrial and commercial areas. Selected photos from our field reconnaissance visit are presented in Appendix A. Many of the small lot residential neighborhoods are drained by curb and gutter. Lot sizes average about 0.15 to 0.25 acres. There is a combination of B-, BB-, and A -type inlets in these neighborhoods, but there does not appear to be a sufficient number of inlets to handle the flows. Floor slab elevations in these small residential neighborhoods appear to be commonly higher than the adjacent street elevation by about 1 to 2 feet. Some typical Mr. Ron Bottoms March 10, 2008 Page 6 of 15 k I o t z associates residential areas are drained by roadside ditch drainage systems with slab elevations generally at or above the natural ground elevations. The large rural -like residential lot neighborhoods are generally north of Spencer Highway and are drained by road side ditches. Floor slab elevations in these neighborhoods arc typically at or above to natural ground levels or road elevation. Some areas have slab elevations below adjacent top of road elevations. The majority of the drainage east of State Highway 146 is a mixture of roadside ditch and storm sewers. Generally, the site inspection identified apparent problems of limited curb inlet capacity and limited or inadequate drainage pathways suitable for effectively relieving excessive accumulations of runoff during severe rainfall events. Conditions also suggested likely inadequate storm sewer capacity. Developments in the older portions of town were typically built without the requirements of detention facilities. New developments are being built to include detention to mitigate the effects of the new development. Short Term Drainage Projects The site visit also confirmed conditions conducive to severe flooding problems in the five short term drainage problems identified by the City. The conditions in and the evaluation of these five critical areas are as follows and are shown on Exhibit 5A: Short Term Drainage Project 1.) Catlett Lane Pavement Replacement Catlett Lane is located off Roseberry Drive and outfalls into Big Island Slough (HCFCD B 106-00-00; see Exhibit 6). The site visit revealed that dead end street of Catlett Lane at Big Island Slough appears to act like a flow restriction to the adjacent neighborhood, which is aggravated by the flat topography of the area. When _the capacity of the limited storm sewer drainage in the area is exceeded it results in backup of runoff waters on surface. Accumulated waters seek the path of least resistance and drain to the lowest intersection of Catlett Land and Roseberry Drive. We understand that City crews recently identified some problems with a drain pipe to some of the existing inlets in the local area that would restrict the drainage capacity of the area. We also know that the inlets to the storm sewer system are small and reduce the inflow into the storm sewer system. An analysis of the complete storm sewer system for this area has not been prepared but our experience is that the capacity of inlets were usually matched to the capacity of the storm sewer system so increasing the throat inlet size may not provide much change in the overall capacity of the system. However the smaller inlets do clog easier due to surface debris. Recently there have been constructed Mr. Ron Bottoms March 10, 2008 Page 7 of 15 k I o t z associates some new telephone and fiber optic stations on the south side of the street which could restrict the ability to construct improvements on the south side of the street. The City provided Klotz Associates a plan dated 2-21-08 for this location that is aimed at removing a blockage to overland or sheet flow and will be helpful when the street becomes full during heavy rainfall events. Klotz Associates agrees that enhanced sheet flood relief paths are helpful to release waters backing up on streets from overflowing sewers. The drawing the City provided shows that about 94 feet of Catlett Street will be removed at the east end of Catlett and then rebuilt at a lower elevation to provide a sheet flow path for the local drainage system. Two residential driveways will have to be adjusted to account for the changes to the lowered roadway. The City did not indicate any changes to the underground storm sewer system, but increased sewer capacity would reduce the amount of backup surface water which currently sheet flows across the area. The previous embankment on the west edge of Big Island Slough has been cut down somewhat and a small swale exists on the south edge to the ditch. This area could be enlarged to provide some additional flow capacity but during high flow conditions there could be large amounts of flow trying to get through that small area. An easement may also be required to address the path of sheet flow in the restricted area. We feel that the current City plan for this location does have merit and some adjustments could be made to the current plans to make the proposed project as effective as possible. Listed below are some comments to the current City plans: 1. Was a new or enlargement to a storm sewer line investigated for this location that could convey the drainage area flows and not require that the street be removed and constructed and a lower elevation? A new or enlarged storm sewer would still require some work within the street and would require more inlets and curb cuts to make use of the larger or new storm sewer. 2. How was the location and elevation determined for the roadway removal? A review of the proposed grading shows that the revised roadway could still pond up to an elevation of 18.08 which still could pond in the street up to 1.3 feet at the intersection of Rosemary and Catlett. Removing more of the road to lower the ponding elevation could reduce the ponding but will require more excavation and construction costs than currently shown on the plans. Removing 25' more of pavement could reduce the ponding elevation by about 0.3' to 1.0'. What was the target water surface elevation or target house slab elevation? The plans indicate that the slab elevations of the two homes shown on the plan are approximately 20.1 and 20.4. 3. Has there been coordination with the owners of the two driveways to make sure they arc agreeable to the local changes and interim impact to them during construction? 4. Have the grades been checked to make sure that the new proposed grades for the driveways will work for the homeowners and their vehicles compared to the new lower roadway elevation? Mr. Ron Bottoms March 10, 2008 Page 8 of 15 k I o t z associates 5. Do you need to replace the concrete roadway with concrete? This will be a low traffic area. Would asphalt pavement be more economical at this location and if so will asphalt be acceptable to the residents? Recommend that the City consider an option of evaluating utilities to determine if construction of a short section of storm sewer on the north side of the road. The new storm sewer would need a new or upsized outfall. The new storm sewer would be placed outside of the pavement but within the street ROW plus additional inlets would be added to utilize the new capacity of the storm sewer. This option could be constructed without removing the concrete street and could provide much more storm sewer capacity to the area at a reduced cost. A driveway to the back yard of one house would probably need to be removed and replaced. Coordination with HCFCD will be required if a new outfall pipe is constructed. Short Term Drainage Project 2.) Creekmont Park Overflow Path The City Park is located at Willow Creek Drive (see Exhibit 7). The park has a parking lot slab which has an elevation higher than the street elevation leading into the parking area. As a result, the natural drainage down the street toward the parking lot is impeded and flow backs up in the street and eventually adjacent properties. From examination of the LiDAR contours in Exhibit 7, it appears that the natural flow path is through the City Park and into Big Island Slough but the parking lot is acting like a restriction to the overland flow capacity. Currently the park was planned to drain north then east to a small shallow outfall ditch that meanders behind homes and makes its way to Big Island SIough. The park with the constructed some elevated trails currently drains poorly and has standing water or wet areas in portions of the park. The park area also needs improved drainage. The City informed us that they plan to lower the parking lot elevation and convey the accumulating surface runoff away from Willow Creek Drive and through the park to Big Island Slough. Several options exist to help address the local flooding situation. One solution is to improve the current drainage path by constructing a larger open ditch drainage system to Big Island Slough, by constructing a storm sewer system along the path of the current open ditch or by constructing a storm sewer from the Park directly north to H Street. Each of the options listed above the merit and different costs. There exists benefits to all the property owners along the outfall path by the improved drainage system provide for better drainage all the way to Big Island Slough. The requirements of each solution would be enough depth and capacity to drain the Willow Creek Drive area. An open ditch relief path along the current drainage path could work but additional ROW would probably be required to build a larger open ditch. This solution my be economical if additional ROW is available from all the property owners from the Park east to Big Island Slough. Mr. Ron Bottoms March 10, 2008 Page 9 of 15 k I o t z associates A storm sewered pipe system along this same alignment could also work but construction easements would be needed to place the pipe. This would probably be more expensive than the open ditch system but would require less ROW. Constructing a storm sewer system from the Park due north across the park to H Street would require an easement across one of the properties due north from the Park. Additionally the drainage along H Street will have to be evaluated to make sure that what ever improvements are made that the street drainage can be improved to handle the drainage. This project would be the shortest distance and may prove to me more economical to construct if one of the property owners works with the City on the alignment and acquisitions of the needed ROW and if the H Street drainage can be improved to handle the flows. Recommend that the City work with one of the property owners due north of the Park to determine if a suitable and available ROW can be worked out along this shorter path. This may prove to be the best alignment. Coordination with HCFCD will be required if a new outfall pipe is constructed. Short Term Drainage Project 3. Drainer e Im ravemerrts alon Dri twood Dave This area is located between Fairmont Parkway and Spencer Highway (see Exhibit 8). The area is drained by a storm sewer system. Currently the storm sewer from areas north of the detention basin sends flows through the storm sewer in a southerly direction. During rainfall events, some of the southbound flows intersect the existing manhole, head west, and then go to a HCFCD ditch while some of the flows backup eastward into the detention basin on the east side of the road. There is also a storm sewer system that conveys flows northward toward the detention basin from areas south of the basin. Drainage plans show the existing two storm sewer systems (48" from the north and 36" from the south). During heavy rainfall events water backs up in Driftwood Drive with some flows coming to Driftwood Drive from the Fleetwood Drive area making the ponding along Driftwood even worse. Remedy of the current flooding problems should consider enlarging the sewer outfall pipe from Mesquite to the ditch and detention basin to provide for sheet flow in this same area. Relief sheet flow pathways for backup runoff waters could include buyout of the house at the intersection of Mesquite and Driftwood. The City provided Klotz Associates a set of plans dated 2-21-08 that is aimed at relieving some of the hydraulic impacts along Driftwood Drive. The drainage plans show a new 36" outfall from Driftwood into the detention basin. Comments to the current City plans: 1. The plans show the existing two storm sewer systems (48" from the north and 36" from the south). Are those two systems connected together under the road? If not it might be Mr. Ron Bottoms March 10, 2008 Page 10 of 15 kIotz��/jassociate5 good to hydraulically evaluate connecting both storm sewer systems to see what benefits might be derived by the connection. 2. The plans show utilities in the area when the outfall pipes arc proposed. Will utility adjustments to be needed to 12" water line, SBC line, electrical line or other utilities at the two new proposed outfalls? 3. The plans show a new junction box, near the existing 60" and 36" outfalls, to divert the flows from the north more directly into the basin. We discussed the possibility of using HDPE pipe in the area that is not under the pavement and also placing a weir type structure in the new junction box to force low flows into the basin. Could these two items be considered for the project to make it easier and more economical to construct and to make more use of the detention basin volumes? Recommend adding rip rap to the end of both new outfall pipes for this project to reduce erosion potential. Should the pipc(s) be extended to go more fully into the detention basin? 4. The proposed outfall could be directed at a 30 to 45 degree angle (not 90 degrees as currently shown on the plans) from the road into the basin to make the flow transition from the storm sewer into the basin easier and thereby reducing the HGL of the system. 5. A curb cut could be provided from the low spot(s) of the road to allow ponded flows to get off of the road and into the detention basin or ditch easier, thereby reducing the ponding depth in the roadway. However, the sidewalk elevation would require adjustment to provide the desired sheet flow path. Appropriate erosion control measures would also need to be included in the improvements. The project as currently designed by the City may not produce the desired reduction in ponding depths. It is our opinion that an overland or sheet flow path is needed to drain the collective areas from Mesquite Street south. Recommend that curb cuts and overland sheet flow paths be constructed from Driftwood into the outfall ditch and another overland sheet flow path be constructed from Driftwood into the detention pond to the east. Both of these two overland or sheet flow paths should help to drain the street easier during major rainfall events and could be constructed today with minimal cost. Other more expensive options exist to the drainage and to address sheet flow or overland flow include: 1.) including an above ground sheet flow path along the west edge of Driftwood, adjacent to the roadway, to the outfall ditch, 2.) lowering a portion of Driftwood to the outfall ditch or by 3.) adding in a larger pipe from Mesquite Street to the outfall ditch or to the detention basin. Each of these other options are more expensive and would require more easements. Recommend that further evaluation be prepared of these other options. Coordination with HCFCD will be required if a new outfall pipe is constructcd. Short Term Drainage Project 4.) Fleetwood Drive Qut all Pipe Upa•izin Fleetwood Drive is located near Driftwood Drive (see Exhibit 9). The City has informed Klotz Associates about a city project for upsizing the outfall of Fleetwood Drive. Currently the outfall pipe is a 60 inch pipe and serves an area of approximately 120 acres. Mr. Ron Bottoms March 10, 2008 Page 11 of 15 k I o t z associates At this time, the flow from severe storm event has to travel down Fleetwood Drive, then east down Mesquite Drive, and onto Driftwood Drive. The sheet flow for this area flows to the outfall location but the neighboring lots arc higher than the street and serve to restrict the flow, much like a levee. An emergency flow path, with needed easements, could be built between the houses of Mesquite Street and along the storm sewer of Fleetwood Drive could direct the sheet flow directly to HCFCD B106-02-00. Inlet capacity at the intersections of Fleetwood Drive is also limited, so another option to consider is adding additional sewer capacity using a pipe or pipes between houses. Recommend that discussions be held with the property owners of the two lots where the sheet flow path of new outfall pipe might be constructed to determine their willingness to work with the City on a potential solution for this area. Short Term Drainage Project 5. Glen Meadows Subdivision Interceptor Inlet Glen Meadows Subdivision is located off Spencer Highway and drains into Big Island Slough by a storm sewer system (see Exhibit 10). Spencer Highway is higher in elevation than this subdivision and some sheet flow drains from Spencer Highway into Glen Meadows. The intersection of Spencer Highway and Valley Brook Drive is a high point which allows ponding water trying to drain off of Spencer Highway. We reviewed the information of the storm sewer system for this area and noted only 9 inlets exist along Valleybrook. During heavy rainfall events the water from upstream areas will sheet flow south along Valleybrook to the lowest point near Meadow Crest Street. The available information indicates that the storm sewer system will surcharge and that there is no relief route for the flows to get out of this portion of Glen Meadows without flooding of some homes. Upsizing of the outfall pipe or a sheet flow path between a couple of homes appear to be good solution for drainage. The City has informed Klotz Associates that an intercept inlet(s) may be added to the Spencer Road drainage system. Adding inlets would increase the capacity which would allow the sheet flow to enter the storm sewer system and thus help to reduce the surface ponding in that area. Additional coordination with the County should continue to determine any future plans they may have for this area. Recommend coordination with the County on their potential work in the area along with a detailed evaluation to determine if a new larger pipe and or sheet flow path is best or if a drainage pipe could be economically constructed south along Valleybrook to Spencer Road then to Big Island Slough. Coordination with HCFCD will be required if a new outfall pipe is constructed. Mr. Ron Bottoms March 10, 2008 Page 12 of 15 Subdivisions with Repetitive Losses Locations k I o t z associates Tropical Storm AIlison and Tropical Storm Erin created major damage to the citizen of La Porte. Exhibit 5 shows the available information on structures and homes that were damage by flooding. Listed below are discussions of several subdivisions that contain repetitive loss properties. Brookglen Subdivision Brookglen Subdivision is located in the west areas of La Porte and the subdivision drains into Willow Springs Bayou HCFCD B 112-00-00. The homes and structures in Brookglen Subdivision were built to previous standards and appear to have the problem of no emergency overflow path. At the cud -de -sac of Gladwyne Drive, the only way for sheet flow to go is into an inlet. The homes and structures are high enough from the road but the water is just ponding. The elevated houses are acting like a levee and retaining the storm water on the street. An overflow path is needed for this area. Exhibit 1 I shows the repetitive losses and the home flooded by Tropical Storm Allison and Erin. HCFCD B 112-02-00 was interconnected to HCFCD B 109-03-00. Creekmont Subdivision Creekmont Subdivision is located off of Spencer Highway and drains into Big Island Slough (HCFCD B 106-00-00). Creekmont Subdivision has the problem of not enough inlets and no emergency overflow path. The homes along Heather Springs are noticeably higher then the street elevation and also adjacent to the bank of Big island Slough. The storm water has to enter the storm sewer of Creekmont Subdivision until it piles up to overtop bank at which water is already in home. An emergency overflow path is needed for this area. Exhibit 12 shows the repetitive losses and the home flooded by Tropical Storm Allison and Erin. Glen Meadows Subdivision Glen Meadows subdivision is located off of Spencer Highway and drainages into Big Island Slough (HCFCD B 106-00-00). The homes in Glen Meadows subdivision have the same problem of no emergency flow paths. The water piles in the streets until it goes into the storm sewer along Valley Brook or overtops the banks of Big Island Slough (HCFCD B 106-00-00). There are limited inlets in the subdivision as well. The homes are higher than the street elevation. The only flow path for the storm water to go is through the storm sewer. Exhibit 13 shows the repetitive losses and the home flooded by Tropical Storm Allison and Erin. Mr. Ron Bottoms March 10, 2008 Page 13 of 15 Fairmont East Subdivision kIotzIF) assoCiates Fairmont East Subdivision is located off of Fairmont Parkway and drainages into HCFCD B106-02-00. Exhibit 14 shows the repetitive losses and the home flooded by Tropical Storm Allison and Erin. The problems for this subdivision appear to be not enough inlets, inadequate storm sewer system and no emergency overflow path. The houses are about I to 2 foot higher than the road elevation. Fairmont West Subdivision Fairmont West Subdivision is located off of Fairmont Parkway and drainages into Big Island Slough (HCFCD B 106-00-00). Exhibit 15 shows the repetitive losses and the home flooded by Tropical Storm Allison and Erin. This subdivision is also in need of a overflow path to let the water out of the subdivision during high flow conditions. Observations on City Drainage Design Procedures The City does have a formal drainage criteria manual to guide design of drainage facilities. At current time, the City Engineer, with the assistance of City staff, evaluates proposed land development and drainage facilities for such development on a case -by - case basis. Appendix D shows the entire criteria manual. Recommend updating the drainage criteria manual to address several drainage related issues, such as overland flow evaluations. The update to this manual should begin immediately and should be commented on my staff and other interests. Ownership and Maintenance There are 7 HCFCD in Clear Creek Watershed, 9 HCFCD in Armand Watershed, 16 HCFCD in San Jancinto/Galveston Watershed in the City of La Porte. The ownership of the channels is listed in the following table. Maintenance is just assumed that the owner will maintain it. See the exhibit for the ownership of channels in the Appendix E. Clear Creek Watershed Ownership Maintenance_ A104-00-00 Taylor Bayou) HCFCD HCFCD A104-07-00 (Tributary 3.93 to Taylor Bayou) HCFCD/City HCFCD/City A 104-07-01 City City A104-10-00 (Boggy Gully/Bayou) HCFCD HCFCD A104-10-02 HCFCD HCFCD A104-12-00 HCFCD HCFCD A104-12-01 HCFCD _ HCFCD Armand Bayou Watershed B106-00-00 (Big Island Slough) HCFCD HCFCD Mr. Ron Bottoms March 10, 2008 Page 14 of 15 k I o t z associates B 106-02-00 HCFCD I ICFCD B106-05-00 HCFCD/City HCFCD/City B 106-06-00 City City B109-00-00 (Spring Gully) HCFCD HCFCD B 109-03-00 (B 112-02-00 Interconnect) HCFCD HCFCD B 112-00-00 (Willow Springs Bayou) HCFCD HCFCD B 112-02-00 (Tributary 1.78 to Willow Spring Bayou) HCFCD HCFCD B112-05-00 HCFCD HCFCD San Jancinto/Glaveston Bay Watershed _ F101-00-00 HCFCD HCFCD F 101-01-00 City City F 10I-03-00 City City F101-06-00 HCFCD HCFCD F101-06-02 HCFCD HCFCD F101-06-03 HCFCD HCFCD F 10 1 -07-00 City City F101-08-00 City City F210-00-00 HCFCD _ I ICFCD F212-00-00 (Deer Creek) HCFCD/City I-ICFCD/City F216-00-00 (Little Cedar Bayou) HCFCD/City I-ICFCD/City F216-01-00 City City F216-02-00 City City F216-04-00 City City HCFCD: Harris County Flood Control District City: City of La Porte Conclusion Pursuant to Tasks 1.1 through 1.7 of the scope for the CWDS, data and site information have been collected to identify and asses apparent current drainage problems in the City. Inadequate inlet numbers and capacities, development in topographically low areas, and inadequate pathways for relief of excessive floodwater accumulations appear to be primary reasons for current drainage problems. As we move into the next phase of the CWDS, we will begin identifying options to resolve the current problems and address ways to prevent future additional drainage and flooding problems. We are available to discuss this report with you at your convenience. We have a significant amount of data used to develop this report. Some summary data has been Mr. Ron Bottoms March 10, 2008 Page 15 of 15 k I o t z associates included in the exhibits and appendices however much more data is available. We look forward to moving into the next phase of work. Sin erely, Z4 Gary L. truzick, P.E., CFM Vice President GLS Attachments CC: Mr. Steve Gillett, City of La Porte Mr. John Joerns, City of La Porte Mr. Rodney Slaton, City of La Porte N Liberty 0 40,000 Feet 249 10 ?90HarrisChambers City of La Porte City -of, ouston Trinity Bay; a er co coort end Galveston Bay 6 I Brazori k I o t z associates VICINITY MAP CITY OF LA PORTE CITY-WIDE DRAINAGE STUDY I KLOTZ PROJ. NO.: 0127.008.000 EXHIBIT 1000, SCALE: 1"= 82885' DATE. MARCH 2O08 Kr. . { gL ne >,. u1 26pol l 4 ;, w k i o m'F 8 .w a a 6 .°6 s a a. F r v.e s 30 u t o a , r 2` 6 P r s w e z v r' i� K � z z x a� r r ,rj m n at)s C C ma F ti r � w x x t € a a ' a FE i k h F r a- kl i Z a �s 1C � T r c� KNOWN 14 N .F � E ALTVATO '+•u k43 r d � $f > Z Sz .F1fl/4'fE '`�k—ay xAr ':a v 0,� r f Ali G 2 14 k I o t z a s s o c i a t e s CONTOURS LiDAR Based Contours CITY OF LA PORTE CITY-WIDE DRAINAGE STUDY KLOTZPROJ. No.:0127.008.000 EXHIBIT SCALE. 1" = 4,0003 DATE: MARCH 2O08 G104-09-00 .' m,-r M 1 - ' Q. __ x 03 x ra CD M c B114-01-00 1 1 -— M x SPEN ER Y" 4 c B K z z I r 1 �. . xAd "o. M "mot,- k I o t z associates c CAB MC rAB x D r t o� FEMA Flood Plain Map rr B w ' KNOWN S R` CITY OF LA PORTE tj -f {BOA CITY-WIDE DRAINAGE STUDY - KLOTZ PROJ. NO.: W27.008.000 EXHIBIT if ,� SCALE: 1" = 3000 DATE. MARCH 2nnS Short Term Drainage Porject 2 /1 .- - - 1 - .-- - ._ t M _ .- 1 - n .. _ ._ t _ ... rn _ t 1_ li081N `Er H C 1. O 0 Opti 105-05-00 Short Term Drainage Porject 1 Catlett Lane P avement Keoiacement F� ANT RIM � P GP��.t55 A Ghi LE- � P� C.� on TSERE Locations O TSARP Locations Severely Damaged Homes Streets Open Channel Drainage B1 100 Year Flood Plain C Ity ■ M VSh Term Drainage Porject 5Meadows Subdivision Im Short Term Drainage Porject 3 Drainage Improvements along Detention Pond Interceptor Inlet ON k I o t z 010 a s s o c i a t e s Short Term Drainage Projects CITY OF LA PORTE CITY-WIDE DRAINAGE STUDY KLOTZ PROJ. No.: 0127. 008. 000 EXHIBIT SCALE. 1" = 4000' S A DATE. MARCH 2O08 Creekmont Brookglen I on Legend TSERE Locations o TSARP Locations Severely Damaged Homes Streets Open Channel Drainage 100 Year Flood Plain 0 C ity I Rl Fairmont East & West Glen Meadows k I o t z 01, 1 0 a s s o c i a t e s Repetitive Losses CITY OF LA PORTE CITY-WIDE DRAINAGE STUDY KLOTZ PROJ. No.: 0127. 008. 000 EXHIBIT SCALE. 1" = 4000' S B DATE. MARCH 2O08 Appendix A Site Visit February 26, 2008 March 6, 2008 2-26-2008 Looking North on Driftwood 2-26-2008 Looking East on Stone Creek Drive Houses are higher than road elevation 2-26-2008 Looking upstream at B 106-00-00 Channel is in great condition 2-26-2008 Looking upstream at B 112-02-00 2-26-2008 Looking at the interconnected between B 112-02-00 and B 109-00-00 that was blocked off 2-26-2008 Looking at roadside ditch in rural residential area. Notice road and house elevations are about the same 2-26-2008 Typical B Inlet on West Main Street. 2-26-2008 Road Side Ditch on South Broadway Street 03-06-2008 Typical B Inlet with Grate Manhole Cover On Roseberry Drive and Catlett Lane 03-06-2008 60 inch and 42 inch Outfall of Detention Pond On Driftwood Drive Appendix B Report Summaries City of La Porte Master Drainage plan Prepared For: City of La Porte Prepared By: O'Malley & Clay, Inc. Consulting Engineers December 1982 Not signed The content of this report include the presentation of recommended drainage design criteria description of drainage areas, runoff computations, recommended channel improvements, proposed drainage structures and cost estimates. Of primary importance are the maps showing the required channels and structures to handle the storm water runoff according to the design criteria. This Drainage Plan is a dynamis plan, meaning that it is subject to continuously changing conditions. The recommended improvements are based upon certain projected data base. As this data base changes in the future, The Drainage plan should be updated accordingly. This Drainage plan has information from the criteria of 1982 from the city of La Porte. The use of this report is to obtain drainage areas and storm system information from 1983. It does not state if the storm sewer systems are up have adequate capacity. It has cost estimates that are from 1983. The exhibits in this drainage plan show the existing drainage conditions, the runoff volume which must be transported, the flow lines, sizes and slopes of the proposed channels to accommodate the flows, required structures and minimum right-of-way needs. Since then there has been much improvements to the drainage criteria manual to consider new rainfall data and storm events. Drainage conditions and runoff volumes have changed since 1983 The value of this drainage plan is to get the existing conditions from 1982. Driftwood Drive Drainage Study, City of La Porte Pond to Park Project Prepared For: City of La Porte Prepared By: CivilTech Engineering, Inc. June 2004 Signed By: Michael D. Lacy T he purpose od this report is to present the findings of the drainage analysis of Driftwood drive and provide recommendations to the City of La Porte for the street ponding. CivilTech was asked to investigate and determine possible solutions that would alleviate street ponding and better utilize the storage capacity of the existing detention pond. The recommendations are that the receiving channel be cleaned out and properly maintained in the future to allow the system to function better for high frequency storms. The maintenance of this channel is the responsibility of HCFCD, but the City should perform this maintenance if HCFCD refuses to do so. Another recommendation would be to consider upgrading the storm sewer system on Driftwood Dr. in the near future. The three-year design frequency should be met at an absolute minimum to eliminate street ponding in high frequency events and to protect against structural flooding in extreme events. Master Drainage Plan and Interim Improvement Recommendations for Unit F101-00-00 La Porte, Texas Prepared For: Harris County Flood Control District Prepared By: Landev Engineers, Inc. September 1987 Not Signed The primary objectives of the study are to determine drainage improvement requirements for the f101-00-00 system to eliminate any 100 year flooding for the ultimate watershed condition within the City of LaPorte, and to recommend interim improvements consistent with this ultimate plan to eliminate flooding for the watershed's existing condition. HEC 1 and HEC 2 models were used for the Armand Bayou watershed. The Southern Pacific Railroad crosses the channel at two locations. Recommendation is regional detention facility that could be located conceivable at the confluence of B 100- 00-00 and B106-00-00. The baseline condition 100 year Water Surface Elevations was not determined in this study. Alternatives are regional detention storage, diversion flow to another system, structural improvements. There are several regional detention locations recommended and diversion that could be implemented. Hydrologic and Hydraulic Study for Interconnect of HCFC Unit B 112-02-00 to Unit B109-00-00 and HCFC Regional Detention Site Unit B512-01-00 Prepared For: Harris County Flood Control District Prepared By: Wilbus Smith Associates, Consulting Engineers and Planners April 1997 Seal Engineer: Melvin G. Spinks, P.E. This is an analysis on Armand Bayou and its streams. A regional detention site addresses the mitigation needs to offset and increase in flows due to the interconnection, the proposed East Boulevard Roadway, and flood protection for the downstream residents in the Brookglen Subdivision and the Spencer Highway estate subdivision. The sub - watersheds are B 11202A, B 109A, and B 112B. The recommended ultimate plan addressed (1) the detention storage for HCFC Regional Detention Site Unit B512-01-00 to serve full development in sub -watershed B 11202A, (2) the full diversion of flows along Tributary 1.78 — Willow Springs Bayou (Unit B 112-02-00) to Spring Gully (Unit B 109-00-00) at the interconnect and (3) the channel improvements required along Unit B 109-00-00 and Unit B 112-02-00 to serve the outflow from the proposed regional detention facility. The channel improvements are concrete lined channel and widening. A HEC 1 and HEC 2 analysis was done for this project. The detention pond will have maximum available detention storage of 320 acre-feet at an elevation of 24.6 feet (1973 NGVD adjustment). Base pond elevation is 15.5 (1973 NGVD adjustment). Missing Information: Technical Appendices — Volumes 1 and 2 Site visit shows that the interconnection was constructed and but has been closed Hydrologic & Hydraulic Analysis Port Crossing Development Prepared For: Port crossing land, L.P. Prepared By: Goldston Engineering, Inc. June 2006 Location : West Fairmont Parkway and 146 The Port Crossing Land, L.P. contracted Goldston Engineering, Inc. to provide supplementary hydrologic and hydraulic consulting services for the Port Crossing Development. The project area and area of analysis fall under the jurisdiction of the City of La Porte, Texas. Ultimate outfall into the Taylor Bayou (HCFC Unit A104-00-00) calls for a drainage analysis that confirms the proposed development is designed in accordance with the policies, guidelines and criteria of the jurisdictional agency in conjuction with oversight review and approval of the Harris County Flood Control District. The developer plans to develop the tract for business, industrial and commercial uses. The Restricted Reserve Detention Basin North (7.34 acres) is for 118.65 acre with 29.49 acres that will be fully developed and will have two wet bottom ponds. The storage volume is 47.71 acre-feet at full bank capacity, which is the equivalent of a storage rate of 1.59 acre-feet/acre due to restricted Taylor Bayou 10-year and 100-year pre -development release criteria. The Restricted Reserved Detention Basin South 22.75 (acres) is for 267.33 acres of fully developed runoff and provides regional detention for the 430 acres that comprise the HCFC A104AI sub -area. The storage volume is 224.30 acre-feet at full bank capacity with a storage rate is 0.82 acre-feet/acre due to restricted Taylor Bayou 10-year and 100-year pre -development release criteria. A trapezoidal conveyance channel will carry runoff north to south from the detention ponds. It will have a 0.001154 channel slope with a 6 foot bottom width and 8 to 10 feet depth and concrete bottom lined. It appears that this report is marked up for review, substantial comments are made. Hydraulic Analysis for Little Cedar Bayou Watershed HCFCD Unit F216-00-00 Prepared For: Harris County Flood Control District Prepared By: Binkley & Barfield, Inc. Consulting Engineers January 2000 Location: Bay from West Fairmont Parkway pass Spencer Highway. The addition off linear detention to Little Cedar Bayou upstream of SH 146 can produce a substantial flood control benefit, without adverse effect to the Little Cedar Bayou or adjoining areas. Little Cedar Bayou is within the city limits of the City of La Porte, Texas, and includes 3.2 square miles of land that is approximately half developed. There is an even mixture of commercial and residential development within the watershed, with the bayou running through the more densely developed areas of LaPorte. Little Cedar Bayou is a narrow, winding earthen channel that was straightened and improved with concrete slope paving. Most of the bridge crossing serves as restrictions to the flow, especially at SH 146 where debris collects on a regular basis. The analysis of Little Cedar Bayou watershed revealed that a definite flood control benefit could be gained from implementing channel improvements upstream of SH 146. The proposed improvements that were analyzed in this report included a linear detention pond between SH 146 and "B" Street, lowering the flow line upstream of SH 146, and reshaping the side slopes to 3:1. Two proposed projects were analyzed. The first project included improvements up to the Southern Pacific Railroad. The second project included improvements up to Sens Road. The improvements would cost 3.2 million. HEC 1 and HEC 2 where used for this analysis. Preliminary Analysis for F216-00-00 Linear Detention Prepared For: City of La Porte Prepared By: Binkley & Barfield, Inc. Consulting Engineers November 2004 Signed By: John G. Fowler This report is a recommendation from the previous report entitled "Hydraulic Analysis for Little Cedar Bayou Watershed HCFCD Unit F216-00-00". The proposed detention pond can perform one of the following functions. When the detention pond is installed with no other channel improvements, the flows downstream of the pond are reduced sufficiently to provide an expected reduction in the 100-year water surface of up to 0.5' downstream of SH 146. When channel improvements in F216 upstream of Spencer Highway are installed, the added conveyance in the channel will deliver more water downstream much more rapidly, serving to reduce potential flooding problems upstream of Spencer Highway. By installing the proposed detention pond in conjunction with these channel improvements, the increased flow in F216 is fully mitigated, and there are no water surface increases downstream of SH 146. If additional development is allowed in the F216 watershed upstream of SH 146, the proposed pond will mitigate much (but not all) of the increase runoff that may be caused by such development. The models created during the detailed design of the proposed detention pond will be structured to reflect the excepted function of the pond when constructed according to the design plans. Drainage Report — Impact and Mitigation Analysis San Jacinto and Galveston Bay Watershed; Proposed Fairmont Parkway Improvements From 161h Street to state HW 146 Prepared For: Harris County Prepared By: TSC Engineering Company December 2005 Signed By: Brian X Tao Drainage impacts caused by the proposed roadway improvements are identified in terms of 10-year and 100-year peak flow. There will be mitigated by providing additional detention storage in enlarged ditches and storm sewers for the proposed roadway improvements. In addition, as part of the roadway improvements, the storm sewers along Fairmont Parkway will be replaced from 161h Street to SH 146. The proposed storm sewers are sized and designed based on the City of Houston's 3-year frequency rainfall runoff curve s-509 and standard Harris County criteria. The proposed roadway project is within the Little Cedar Bayou watershed, a sub watershed to San Jacinto and Galveston Bay Watershed. The project drainage area drains into a 65" x 40" arch pipe storm sewer under SH 146, then drains eastward to discharge into the Little Cedar Bayou (HCFCD Unit F216-00-00). For areas along Fairmont Parkway between UPRR and 161h Street, the flow is collected through roadside/median ditches, then discharge into roadside/median ditches along Fairmont Parkway east of 161h street. Currently, TxDOT constructs the overpass project in this portion of Fairmont Parkway. For areas along 161h Street north and south of Fairmont Parkway, the flow is collected through roadside ditch, then discharged into roadside ditches along Fairmonth Parkway east of 161h Street. Hydraulic Analysis for Sens Road From 300' North of Spencer HWY. to 300' North of Avenue "H" HCPID Pin Cl/102/1002/005; Little Cedar Bayou (F216-00-00) & HCFCD Channel A104-07-00 Prepared For: Harris County Flood Control District Prepared By: Binkley & Barfield, Inc. Consulting Engineers February 2005 Signed By: Joel R. Colwell The current analysis addresses detention requirements for mitigation of increased flows from the proposed improvements to Sens Road, Bay Area Boulevard and Fairmonth Parkway. Sens Road will be designed with a storm sewer system that diverts a substantial amount of storm water flow to the south of Spencer Highway system, continuing into the proposed median ditch at Bay Area Boulevard, and into HCFCD A104-07-00. The increase flows from this combination of projects will require the installation of a 155 acre-foot detention basin downstream of Fairmont Parkway near the south side of the first major rail crossing of channel A104-07-00. There may be a need for a regional pond in this area to accommodate future drainage improvements to the area. The recommendation is made that the drainage from Sens Road, Fairmont Parkway, Bay Area Boulevard, and A104-07-00 combined and this would require only one detention facility, with a single inflow weir and outflow structure. The 80 acre site is much larger than the area required for the detention discussed but can possibly serve as a regional facility. Hydraulic Analysis for Sens Road From 300' North of Spencer HWY. to 300' North of Avenue "H" HCPID Pin Cl/102/1002/005 Volume 2 Prepared For: Harris County Flood Control District Prepared By: Binkley & Barfield, Inc. Consulting Engineers December 2003 Klotz Associates was not given Volume 1 Volume 2 contains the following: ■ Appendix B o Phase I Environmental site assessment o Wetland Delination o Endangered Species Inquiry o Antiquities Permit o Archeological Survey o Archeological Evaluation ■ Appendix C o Geotechnical Report — Sens Road o Geotechnical Report — Little Cedar Bayou ■ Appendix D o Hydraulic and Hydrological Study ■ Appendix E o Design Documents Taylor Bayou Watershed Master Drainage Plan; Tax Increment Reinvestment Zone #1, La Porte, Texas Prepared For: City of La Porte Prepared By: CivilTech Engineering, Inc. August 2003 Signed By John D. Conquest This report presents technical analyses and findings relative to the impact of the proposed development of the Taylor Bayou Watershed and City of La Porte Tax Increment Reinvestment Zone #1. It also addresses the proposed channels, waterway corridors and detention facilities to convey and mitigate the potential impacts. A Master Drainage Plan was developed for the Tax Increment Reinvestment Zone #1 (TIRZ) and areas contributing to the Taylor Bayou watershed within the City of La Porte. This master drainage plan addresses mitigation and drainage infrastructure requirements and consists of a complete impact analysis for the ultimate development of the TIRZ. A detailed watershed analysis was performed using HEC-1 computer models. The impact analysis concluded that the proposed development of the TIRZ would increase peak flows in Taylor Bayou at the confluence of Taylor Bayou (HCFC Unit A104-00-00) and HCFC Unit A104-012-01 by 1,122 cfs. The routing analysis concluded that approximately 325 ac-ft of detention mitigation would be required to offset the increase in peak flows due to the TIRZ development. The drainage analysis determined that three separate detention ponds and two waterway corridors totaling about 104 acres in size will provide the necessary detention volume. Three culvert structures will serve as outfall for the detention ponds. Clear Creek Watershed Regional Control Plan, Volume 2 Prepared For: Harris County Flood Control District & Texas Water Development board Prepared By: Dannenbaum Engineering Corporation February 1992 Klotz Associates was not given Volume 1 Volume 2 contains the following: Section VII - Combination Alternative ■ Descriptions of Alternative ■ Hydrologic and Hydraulic Analysis o Design Criteria o Hydrology ■ Sensitivity Analysis ■ Outlet Expansion ■ Regional Detention o Hydraulics ■ Main Channel ■ Tributaries ■ Cost Analysis ■ Socioeconomic Considerations ■ Environmental Consequences o Main Channel o Tributaries o Armand Bayou o Third Outlet o Mitigative Action 0 Section VIII — Conclusion and Recommendations ■ Summary of Engineering Design Alternatives ■ Summary of Environmental Impacts ■ Recommendations The recommendations based on the study are to implant a combination of the alternative that was recommended. Preliminary Engineering Report For ens Road From 300 Feet North of Spencer Highway to 300 Feet North of Avenue "H" PIN No. Cl/102/1002/005 Prepared For: Harris County Flood Control District Prepared By: Binkley & Barfield, Inc. Consulting Engineers August 2006 The proposed improvements to Sens Road will provide for a 5-lane concrete roadway from approximately 300 feet north of spencer highway to 300 feet north of Avenue "H" for a project length of 3,887 feet. The proposed concrete roadway will be drained by the proposed storm sewer system. The proposed drainage system for Sens Road outfalls within the Project Limits and consists of three storm sewer runs. Two of the runs will outfall into the improved Little Cedar Bayou (HCFCD Unit F216-00-00) and the third one will join the existing box culvert that flows to the south into the Bay Area Boulevard system. The proposed storm sewer system for all areas will consist of the trunk line, leads and proposed inlets. The existing box culvert at Little Cedar Bayou (F216-00-00) will be replaced with a new culvert and outfalls for the tributary two storm sewer systems. Little Cedar Bayou (HCFCD Unit F216-00-00)is proposed to be improved fir storm water mitigation and maintaining the 100-year storm water surface elevation at the existing water surface elevation. The limits of Little Cedar Bayou improvement will be Sens Road on the west and the Union Pacific Railroad to the east. A Storm water detention facility will not be required for Little Cedar Bayou due to the diversion of water from Avenue "D" into the Bay Area Boulevard system. This project also includes a proposed detention basin near Harris County Flood Control District Ditch A104-00-00 and channel improvement on a portion of this ditch. �-1 A - REQUEST FOR CITY COUNCIL AGENDA ITEM Agenda Date Requested: November 12 2007 Requested By: Wa ne J. S o� Department: Planning Report: X Resolution: Ordinance; — Appropriation Source of Funds: NA Account Number: NA Amount Budgeted: NA Exhibits: 4/ 4 SUMMARY The Flooding and Drainage Committee, at their October 29, 2007, meeting directed Staff to bring forward to Council a list of short term drainage projects for near -term consideration and future funding. This list contains the projects, in priority, that Staff feels will have a favorable impact on several areas in La Porte. A power point presentation will be given at the meeting. Cost estimates are preliminary and will be refined when the projects go into design; 1) Lower Catlett Drive at its termination point along Big Island Slough near Roseberry Drive which would help residents in Fairmont Park West. In the past Public Works has cut off some of the top bank in order to lower the ponding elevation impacting the homes at the intersection of Catlett and Roseberry Drive. However, in order to alleviate the recent flooding, it is required to cut the street in order to further decrease the ponding elevation. There are two options to the City in this regard. First option is to cut Catlett at one of the two driveways intersecting it and making this the new high point, at which point the new concrete would gently slope down and terminate at its present location. This option would not require the City to replace the two driveways. Jhe second option is to replace the entire length of Catlett from its intersection with Roseberry. This would allow the terminus of Catlett to be further lowered but would result in more concrete being poured as well as the replacement of the two existing driveways from one of the existing joints. The first option would cost roughly $10,000 while the second would cost $65,000. Planning Department is currently analyzing how much mor drop �can be obta� fro implementing Option II in order to determine if the benefit warrants the cos .�"$" a 2) filer the parking lot accessing the City Park at the end of Willow Creek Drive in Creekmont Section II. T1@400-year event in this area is sheet flowing through the park in order to access City maintained ditches which ultimately outfalls into Big Island Slough. The existing parking lot is higher than the GL� finished floor elevations of the homes along Willow Creek and therefore the 100-year event will flood these homes before it is able to sheet flow through the park. Lowering the parking lot and cutting out some of the park will minimize this, The cost for this project is approximately $35,000 and includes the excavation costs associated with the park. Another separate project being suggested by Parks would improve the conveyance to Big Island Slough. 3) Replace the junction box along Driftwood Drive in order for the storm runoff from Fairmont Park East to discharge directly into the detention pond along Driftwood, thereby decreasing energy losses and allowing more water to be taken off Driftwood. In conjunction with this, replace one of the outfall pipes to B 106-02, a tributary of Big Island Slough, with a larger pipe. The impact -to B 106-02 would actually decrease because of the time it would take for the detention pond to fill versus the present situation of the storm runoff discharging directly to B 106-02. Engineering division has run the calculations verifying this assertion. The cost for this project would be approximately $35,000. 4) Upsize the outfall pipe discharging Fleetwood Drive to 13106-02, potentially helping residents in Fairmont Park East. This would decrease energy losses in this drainage system. However, since Fleetwood Drive is the street intended to sheet flow the storm runoff to its ultimate outfall for this area but is higher than the streets connecting to it, this project should be considered low priority and may not impart any immediate benefit until further improvements along Fleetwood are implemented (i.e. lowering the street). The cost for this project would be approximately $30,000 and would use pipe bursting technology. More research is necessary. 5) The intersection of Spencer Highway and Valley Brook Dr. appears to be a high point which allows ponding water trying to drain off of Spencer Highway to sheet flow into the Glen Meadows Subdivision and adding to the volume of water already draining from the streets of that subdivision into Big Island ` Slough. Since the drainage system associated with Spencer Highway is designed to drain from the street into Big Island Slough, Staff is suggesting to Harris County that an interceptor inlet be added to the system just West of that intersection and along the North curb line at the foot of the bridge going over Big Island Slough. This interceptor inlet would allow water to drain off Spencer Highway directly into the storm sewer and discharge from the box culvert outfall structure as intended. Staff is also coordinating an addition to the outfall structure at Spencer Highway and Big Island Slough to account for additional sheet flow for major rain events. The total estimated costs for these projects range from $110,000 to 165 00 epending on further analysis and design. A Notice of Interest (NOI) is being forwarded in hopes to secure grant funding from the latest disaster declaration. This funding may be used as a reimbursement should Council direct Staff to proceed with design and funding recommendations. The Planning Department, in coordination with the Public Works, Parks and Police Departments is researching surrounding city ordinances to determine the best method, practices and enforcement to control and prevent speeding traffic from flooding homes due to the wakes being created. Results will be presented to the Committee at their December 3, 2007, meeting. Action Required by Council: Direct and guide Staff on how to proceed with the analysis, design and funding recommendations for the short term drainage projects reviewed by the Flooding and Drainage Committee. Approved for City Council A enda Ron Bottoms, City Manager Date SHORT-TERM DRAINAGE PROJECTS N ' (SPENCER HWY. @ B106-00-00) _NPAF E PROJECT LOCATION 300 600 1,200 SHORT-TERM DRAINAGE PROJECTS N (PRIORITY ONE - CATLETT DRIVE) W, E PROJECT LOCATION 300 600 1,200 300 600 SHORT-TERM DRAINAGE PROJECTS N (PRIORITY TWO - WILLOW CREEK DRIVE) E I 1,200 Fe, H PROJECT LOCATION SHORT-TERM DRAINAGE PROJECTS (PRIORITY THREE - DRIFTWOOD DR.) 300 600 1,200 N W� E s PROJECT LOCATION SHORT-TERM DRAINAGE PROJECTS (PRIORITY FOUR - FLEETWOOD DR.) PROJECT LOCATION 300 600 1,200 Appendix D City of La Porte Drainage Criteria Manual CHAPTER 5 STORM SEWER DESIGN CRITERIA 5.1 GENERAL PROVISIONS Drainage Criteria for development within the City of La Porte, and where applicable within La Porte's Extraterritorial Jurisdiction (E,T.J.) is dependent upon the size and type of development, the conditions within the individual watershed, the conditions or design of the receiving stream, bayou, channel, roadside swale, culvert, or roadway. The basic objective of this policy is to minimize the threat of flooding to areas within the City and its E.T.J. and to minimize the effect of continued development on individual watersheds. 1. The City believes that the best long-term means of accomplishing its objective is a continued program of improvement and extension of the Harris County Flood Control District's system of open channels. This statement recognizes the technical reality that an essential prerequisite to an effective flood control program is a system of open channels capable of carrying storm runoff of any type in Harris County to Galveston Bay without adversely impacting existing urban areas adjacent to the channels. 2. The City recognizes that both District's and City's existing open channel system is, in many instances, inadequate to accomplish the goal of eliminating existing flooding conditions for existing levels of urban development, or for ultimate development in the watershed. 3. The City therefore recommends that where required, certain additional flood control facilities be utilized to supplement the open channel system. Such flood control facilities shall be designed to preclude flooding in areas that do not presently flood and not increase flood levels where flooding now occurs. Specifically, the City supports the use of storm water detention to supplement the open channel system until long-term channel improvements can be completed, or as permanent facilities where additional open channel improvements are not feasible. The result will be that new development will limit or restrict the impact downstream. 5.1.1 All the drainage plans and construction shall meet or exceed the requirements of the City of La Porte, Harris County Flood Control, Harris County, TxDOT, or any other entities having jurisdiction over a facility (i.e. roadway, channel, etc.). 5.1.2 Unless otherwise provided for in these policies, development shall follow the Harris County Flood Control District Criteria Manual for the design of Flood Control and Drainage facilities in Harris County, Texas. 5.1.3 If application of the policies and criteria contained in this document conflict with the City's duties under the Flood Hazard Prevention Ordinance, the regulations of the Flood Hazard Prevention Ordinance shall apply. 5.1.4 Drainage structures shall be constructed in such locations and of such size and dimensions to adequately serve the development and the contributing drainage area. In new developments, the developer shall provide all the necessary casements and rights -of -way required for drainage structures, including storm sewer and open or lined channels. 5.2 CONSTRUCTION PLAN REQULREMENTS 5.2.1 A drainage map shall be included in the construction plans. The drainage area map shall include: A. Drainage areas, including areas draining from off -site onto or adjoining the project Stormwater Criteria Page 1 of 10 B. Design storm runoff, based on the type of facility and storm frequency listed in Section 5.4. C. 100 — year runoff D. Route of overland flow including the overflow to a drainage channel or detention facility E. Water surface profiles for the 25-year and/or 100-year storms in the outfall channel. All available information will be considered when making this determination. F. Flow per inlet G. Maximum ponding elevation 5.2.2 Detailed drainage calculations shall be submitted with the construction plans. 5.2.3 A lot grading plan should demonstrate that the finished grading plan will drain to approved collection and discharge points and that the overland flow of water from adjacent properties will not be impacted 5.2.4 The hydraulic gradient for the design storm may be shown on the construction drawings. Calculations for the elevation for the hydraulic gradient shall be provided with the design stonn drainage calculations. The hydraulic gradient must be below the gutter line for the design storm. The tailwater elevations based on a 25-year frequency in the outfall channel shall be used for calculations of the hydraulic gradient. 5.3 USE OF PREVIOUSLY DESIGNED AND INSTALLED INFRASTRUCTURE Situations where previously installed infrastructure is in place but not yet utilized to its design capacity will be considered on a case by case basis. The developers engineer shall after consultation with the City, prepare a report that: a. outline the original design criteria b. evaluates the impact of the original design on the receiving stream, adjoining properties and/or the 100 year Floodplain. Based on the report, the City Engineer may allow full or partial use of the previously installed infrastructure and may require it to be supplemented with detention or other facilities. 5.4 STORM FREQUENCY, RUNOFF AND DATUM A. Storm Frequency All drainage improvements shall be designed for the following storm frequencies. Type of Facility Road Side Ditches and Culverts 3 year Storm Sewers 3 year Ditches & Culverts Drainage 100 acres and more 25 year Bridges 100 year Creeks 100 year Detention Facilities Refer to Section 5.5 B. Storm Runoff Design flow of storm water runoff is to be calculated using the Rational Method. The Rational Method is based on the direct relationship between rainfall and runoff., and the method is expressed by the following equation: Stormwatcr Criteria Page 2 of 10 Q = CIA, where Q is the storm flow at a given point in cubic feet per second (c.f.$). C is a coefficient of runoff (see Table 1). I is the average intensity of rainfall in inches per hour for a period equal to the time of flow from the farthermost point of the drainage area to the point under consideration. (See figure 1, I-D-F Curves and Figure 2, Determination of Time of Concentration) A is the drainage area in acres The size and shape of the watershed must be determined for each installation, The area of each watershed may be determined through the use of planimetric-topographic maps of the area, supplemented by field surveys in areas where topographic data has changed or where the contour interval is insufficient to adequately determine the direction of flow. The outline of the drainage area contributing to the system being designed and outline of the sub -drainage area contributing to each inlet point shall be determined. When calculating the peak flow rate of storm runoff, rainfall intensity will be determined from the rainfall intensity, duration and frequency curves, shown in Figure 1. The stortu frequency used for this determination will be according to the facility to be designed as listed in Section A. Runoff Coefficients and Time of Concentration Runoff coefficients, as shown in Table 1, shall be the minimum used, based on total development under existing land zoning regulations. Where land uses other than those listed in Table 1 are planned, a coefficient shall be developed utilizing values comparable to those shown. Larger coefficients may be used if considered appropriate to the project by the City Engineer. The time of concentration is defined as the longest time, without unreasonable delay, that will be required for a drop of water to flow from the upper limit of a drainage area to the point of concentration. The time of concentration to any point in a storm drainage system is a combination of the "inlet time" and the time of flow in the drain. The inlet time is the time for water to flow over the surface of the ground to the storm drain inlet. Because the area tributary to most storm sewer inlets is relatively small, it is customary in practice to determine the inlet time on the basis of experience under similar conditions. Inlet time decreases as the slope and the imperviousness of the surface increases, and it increases as the distance over which the water has to travel and retention by the contact surfaces, Time of concentration shall be computed from Figure 21n and in no case shall the inlet time be more that the time shown in Tablet. Stormwater Criteria Page 3 of 10 Table 1 Zone Zoning District Name Runoff Coefficient "C" Maximum Inlet Time in Minutes R-1 Low Density Residential 0.50 15 R-2 Mid Density Residential 0.60 15 R-3 High Density Residential 0.80 10 MH Manufactured Housing District 0.55 15 NC Neighborhood Commercial District 0.80 10 GC General Commercial District 0.85 10 BI Business Industrial Park District 0.85 10 LI Light Industrial 0.85 _ 10 fE Heavy Industrial 0.85 10 PUD Planned Unit Development District variable 10 to 15 Miscellaneous Land Uses Land Use Runoff Coefficient "C" Church 0.70 to 0.90 School 0.50 to 0.90 Park 0.30 to 0.70 C. Datum All drainage plans shall be prepared based on United States Geodetic Survey datum, 1978 adjustment, consistent with National Flood Insurance Program, Flood Insurance Study for the City of La Porte. 5.5 REQUIRED DETENTION Detention Basins — Unless otherwise provided for in this Section, Detention Basins will be required for developments within the following watersheds. Little Deer Creek — F212 • Upstream of Main Street Little Cedar Bayou — F216 • Upstream of State Highway 146 Big Island Slough — B106 • All segments Spring Gully — B 109 • All segments Willow Spring Bayou — B 112 • All segments Taylor Bayou — Al04 • All segments The listed watersheds are shown on Figure 3. Stormwater Criteria Page 4 of 10 5.5.1 Design Standards for Detention Basins Detention requirements for developments less than 50 acres shall be according to the following table. For developed areas of 10 acres or less, the required volume equals the total development area times the appropriate storage coefficient. For areas greater than 10 acres and less than 50 acres the volume is determined by applying Harris County Flood Control District criteria for small watersheds. Table 2 Developed Area Storage Coefficient 0 to 3 acres 0.20 acre ft. / acre 3 to 10 acres 0.45 acre ft. / acre 10 to 50 acres per HCFCD criteria For developments larger than 50 acres, Harris county Flood Control District and the City Engineer shall approve the detention facility criteria. 5.2.2 Outlet Sizing The outlet structure shall be designed using the orifice equation as follows: Q = CA x. (2gh)h Where, C=0.8 A — cross sectional area g = 32.2 feet / sec'2 h = head differential For head differential use 2' or the 100-year water surface in pond minus the 25-year water surface in receiving channel, if available. 2. Minimum restrictor shall be 6" diameter. 5.5.3 Additional Standards for Detention Basins The detention facility shall be designed for easy maintenance. For smaller developments the designer is encouraged to use parking lots, underground piping, swales, green spaces, etc. to achieve the volume required. For larger developments every consideration shall be given to designing of the facility for multipurpose use, such as playgrounds, miniparks, required green spaces, etc. to assure that maintenance will be accomplished. The design shall include the following: 1. an earthen detention basin shall have minimum side slopes of 4:1 and a minimum bottom width of ten feet; 2. the bottom of the detention basin shall have a minimum 0.50% cross slope to facilitate quick drainage. 3. a v-shaped trickle channel a minimum of 5' wide, six-inch thick, reinforced concrete shall be constructed through the detention basin at a longitudinal slope of 0.20% to accommodate low flow and facilitate rapid drainage. For developments less than 3 acres, the trickle channel may be 2 feet wide and 4" thick. 4. a minimum 12-foot wide maintenance berm shall be provided around the perimeter of the detention facility. 5. ingress and egress for maintenance including a dedicated right-of-way if required, shall be provided to the detention basin and clearly shown on the construction drawings or site plan subdivision plat. Stormwater Criteria Page 5 of 10 6. the detention basins, slopes, bottom, maintenance berm, and other associated right-of-way shall be final graded with a minimum of 6" top soil the hydro -mulch or drill -seeded and watered to facilitate full grass coverage. 7. parties responsible for maintenance of the detention facility must be shown on the plat or plans. S. Pumped detention systems may be allowed with specific approval from the City Engineer. 5.5.4 Ownership and Maintenance of Facilities The City will not accept maintenance of on site facilities that serve only one tract or development, unless it is determined to have other public benefits, is recommended by staff and approved by the Planning and Zoning Commission. Harris County Flood Control District may, at their discretion, accept maintenance of facilities, provided they are designed in accordance with the District's criteria manual. Requests for Harris County Flood Control District to assume maintenance of any facility should be coordinated with the City prior to any development approvals. 5.6 ADDITIONAL DESIGN REQUIREMENTS 5.6.1 Discharge Points The developer shall terminate all drainage improvements at a discharge point approved by the City. The developer shall design and construct such discharge point, or outlet, to prevent damage to or overflowing into adjacent property. The City may require creek improvement, channel lining, energy dissipaters or other improvements for such outlet to prevent erosion or increase the flow capacity. Finished elevations of new pavement, parking areas, or other improvements shall be designed so that each succeeding high point is lower when moving in a downstream direction. This ensures the 100-year discharge has an unobstructed path to the discharge point whether discharging to a channel or detention pond. 5.6.2 Public Streets as Drainage Facilities 1. Maximum depth of water to be allowed in local streets during design flow shall be at the top crown, or top of curb, whichever is less. 2. Maximum spread of water in collector streets during design flow shall allow for one clear lane of traffic (12 feet wide). 3. Maximum spread of water in arterial streets during design flow shall allow for two clear lanes of traffic (24 feet wide). 5.6.3 Drainage Channels and Structures 1. The developer shall install an underground storm drain on curb and gutter streets beginning at the point where calculated storm water runoff is of such quantity that it exceeds the height specified above. The developer shall construct the storm drain system from the point to an approved outlet. 2. For non -curb and gutter streets, the developer may use open channel (channel or ditch) methods o dispose of storm water specified above. Such channels may be in dedicated draining easements outside the standard street right-of-way upon City approval of the location and alignment of such easements. Alternatively, the developer may widen the street right-of-way to accommodate an open channel of greater capacity than the standard street/ditch section. 3. If the developer locates the channel in a widened street right-of-way, the City shall approve the right-of-way width and channel configuration. the depth of flow in the channel shall not exceed one (1) foot as measured from the ditch flowline to the point on the roadway established as the high water level in this section. Stormwater Criteria Page 6 of 10 4. The developer shall design and construct all channels to terminate at an approved outlet. 5.6.4 Habitable Structures The developer shall provide adequate means for storm water run-off in excess of the "design storm" capacity (i.e., 3, 10-year storm) to flow around habitable structures. a.) The developer shall provide a grading/drainage plan which shows that all building sites can provide a finished floor elevation: (1) At least one foot(l') above the top of the curb using the highest point along the portion of such curb fronting the building site, or (2) At least eighteen inches (18") above the crown of the road elevation, using the highest point along the portion of such road fronting the building site. (3) At least on foot above the ground elevation along all sides of the building site. b.) In addition to paragraph (a) above, the developer shall provide a grading/drainage plan which meets or exceeds the provisions of Chapter 94, Code of Ordinances, Flood Hazard Reduction, c.) The developer shall design and construct all streets to minimize any fill required to bring building pads into compliance with this code. d.) Alternate methods of building protection may be accepted by the City upon submittal of detailed information, review and approval by the City Engineer. 5.6.5 Drainage System Criteria If an underground drainage system is required, and a 60-inch or smaller pipe will handle the design slow, pipe shall be used. If a 60-inch pipe is not adequate, the developer has the option to use concrete pipe or natural and/or a lined drainage channel. If pipe is selected, the maximum allowable velocity shall be 8fps in the pipe. Lining materials, if used, shall be approved by the City. 5.6.6 Public storm sewers are defined as sewers and appurtenances that provide drainage for a public right-of-way, or more than one private tract, and are located in public right-of-way or easement, private storm sewers provide internal drainage for a reserve or other tract. Private storm or sewer connections to public storm sewers shall occur at a manhole or at the back of an inlet as approved by the City Engineer. All private storm sewers within the public right-of-way shall be constructed in conformance with the Standards. 5.6.7 All construction shall conform with the City of La Porte Construction Details. 5.6.8 All storm sewers shall meet or exceed the requirements of the "Drainage Criteria Manual for Harris County, Texas" and the requirements of the City of La Porte. 5.7 LOCATION OF STORM SEWER 5.7.1 Public storm sewers shall be located within a public street right-of-way or storm sewer easement, dedicated to the public and adjoining a public street right-of-way. Storm sewers through side lot drainage easements are highly discouraged. Limited use may be approved at the discretion of the City Engineer. If approved, a minimum twenty -foot (20') wide easement is required (10' on each lot). 5.7.2 Recommended alignment within a public street right-of-way. A- Boulevard pavement section with median — along centerline of the right-of-way. Stormwater Criteria Page 7 of 10 B. Undivided pavement section five feet (5') inside the right-of-way. For storm sewer located in a public street right-of-way, a minimum of two -foot (2') shall be maintained inside the right-of-way line to the outside edge of the stone sewer unless otherwise accompanied by an adjacent easement. C. Alternate locations for a storm sewer will be permitted by the City Engineer. 5,73 Recommend alignment within an exclusive storm sewer easement. A Storm sewers placed in easements shall conform to the requirements of Section 2.4.5 B. Storm sewers within easements shall be placed no closer than five feet (5') measured from the outside edge of the pipe to the edge of an easement, except when adjoining another easement or public right-of-way where the distance may be reduced to two feet (2'). The storm sewer shall be placed in the center of the easement. When the storm sewer easement adjoins a public right-of-way, the easement may be reduced to a minimum of ten feet (10') and the storm sewer may be aligned close to the right-of-way line, as long as required clearances are met, with specific approval of the City Engineer. 5.8 STORM SEWER MATERIALS 5.8.1 Storm sewer and culvert pipe shall be precast reinforced concrete pipe, unless specifically approved by the City Engineer. Concrete pipe shall be manufactured in conformance with the requirements of ASTM C 76, " Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe," current revision. Reinforced concrete pipe shall be Class III or stronger. The design engineer shall provide for increased pipe strength when conditions of the proposed installation exceed the allowable load for Class III pipe. All concrete pipe constructed in water -bearing soil or forty-two inched (42") in diameter or larger, shall have rubber gasket joints meeting the requirements of ANSI/ASTM C 443, "Joints for Circular Concrete Sewer and Culvert pipe, Using Rubber Gaskets", current revision. Concrete pipe with diameter of less than forty-two inches (42") may be installed using pipe with tongue and groove type joint and Ram-nek, or approved equal, as a joint filler. When specifically approved by the City Engineer, reinforced concrete arch and elliptical pipe conforming to ASTM C506 and ASTM C507, respectively, current revision, may be installed in lieu of circular pipe. Reinforced concrete box culverts shall meet the minimum requirements of ASTM C789, "Precast Reinforced Concrete Box Sections for Culverts, Storm Drains, and Sewers", current revision. pipe joints for arch and elliptical pipe and box culverts shall be sealed using Ram-nek or approved equal. 5.8.2 Storm sewer outfalls into open channels shall be constructed using corrugated steel pipe. Corrugated steel pipe shall be manufactured in conformance with the requirements of AASHTO Designation M-36-82, current revision. Pipe material shalt be Aluminized Steel Type 2, meeting the requirements of AASHTO Designation M-27-79L current revision, or Pre -coated Galvanized Steel, AASHTO M-246, 10 mil coating on both sides. All pipe shall have a full double coating, Type A, in accordance with AASHTO Designation M-190, current revision. Pipe joints and fittings shall meet the minimum requirements of these specifications and shall have an O-ring gasket seal meeting the requirements of AASHTO C-361, current revision. (See City of l.a Porte Construction Details). 5.8.3 Storm sewer outfalls shall have a slope protection to prevent erosion. Slope protection may be constructed of slope paving or rip rap. Slope paving shall be four -inch (4") five (5) sack concrete with six-inch by six-inch (6" x 6") welded wire mesh (W14 x W14) or three eighths inch (31") steel rebar on twenty -four -inch (24") centers, each way. Rip rap shall be a minimum of six-inch (6") broken concrete rubble with no exposed steel or well-rounded stone and shall be a minimum of eighteen inched (18") thick. Slope protection texturing shall be required where public access likely. Refer to the Construction Details for minimum dimensions. Stormwater Criteria Page 8 of 10 5.9 ADDITIONAL REQUIREMENTS 5.9.1 Minimum depth of storm sewer (measured to the top of pipe) shall be twenty-four (24") below the top of curb or finished grade, whichever is lower. Minimum size storm sewer for main land and inlet lead shall be eighteen inch (18"). 5.9.2 Storm sewers shall be bedded using cement stabilized sand (See specification in Section 4.2.3) as shown in the City of La Porte Construction Details. 5.9.3 Pipe requirements. A. Reinforced concrete pipe installed at a depth greater that thirty feet (30') shall be designed by the engineer for the specific installation and approved by the City Engineer, Reinforced concrete pipe shall be designed in accordance with the American Concrete Pipe Association, "Concrete Pipe Design Manual", Maximum cover on the pipe shall be measured from the top of pipe to the ultimate finished grade or natural ground, whichever is greater. B. Corrugated steel pipe shall have a minimum thickness as follows: PIPE SIZE MINIMUM THICKNESS (Inches) Corrugations (Inches 242-2/3" X 1/2" 0.052 30- 482-2/3" X 1/21 0.064 54- 723't X 1" or 511 X 1" 0.064 78- 102311 X 1" or 5" X 1" 0.079 Bedding for corrugated steel pipe shall be cement -stabilized sand. Corrugated steel pipe less than or equal to fifty-four inches (54") in diameter and less than thirty feet (30') deep shall have the minimum thickness given above. C. Design storm flow in a street shall not exceed the capacity of the street, for the water surface equal to the top or curb and shalt not exceed the inlet capacity. Design storm flow shall meet Harris County criteria. D. All bridges must be a minimum of eighteen inches (18") above the 100-year water surface elevation or in accordance with the Federal Emergency Management Agency (FEMA) regulations, latest revisions, or HCFCD requirements, whichever is greater. 5.9.4 Storm sewers less that forty-two inches (42") in diameter shall be constructed on a straight horizontal and vertical alignment between manholes. Storm sewers greater than or equal to forty- two inches (42") in diameter may be laid along a curve using manufactured bends of less than or equal to H 1/4'. 5.10 APPEARANCES 5.10.1 Manholes A. Manholes shall be placed at all changes in alignment, grade and size of the storm sewers; at the intersection of two or more storm sewers; at all inlet leads, and at the end of all storm sewers. B. Maximum spacing between manholes shall be six hundred feet (600') C. Manhole covers shall be cast iron, traffic bearing, type ring and cover with the words "storm sewer" cast into the cover. Stormwater Criteria Page 9 of 10 5.10.2 Inlets A. Curb inlets shall be spaced and sized to intercept the calculated runoff for the design storm. The water surface elevation at the inlet shall be less than or equal to the top of curb for the design storm flow. B. Maximum travel distance of water in the street to a curb inlet shall be three hundred feet (300') on a major thoroughfare and in a commercial area. The maximum travel distance of water in the street permitted in a single-family residential area shall be four hundred feet (400'). C. No Valley Gutter without prior approval. D. Curb inlets should be on the intersecting side street at intersections with a major thoroughfare. The City Engineer shall specifically approve locations at intersections. E. Grated inlets will not be permitted in an open ditch. E. Backslope swale interceptors shall be placed in accordance with the requirements of Harris County. G. Curb inlets shall have solid inlet lids. Grate or Curb and Grate inlets shall not be allowed for residential subdivisions. Curb inlets shall be recessed, unless otherwise directed by the City Engineer, H. Backfill around inlets and to top of first stage inlet with cement stabilized sand. Stormwater Criteria Page 10 of 10 �m i cu �E: z >o �1A- L4 u nr s Li C 5GC} tz a GO 3' 37co ' � v: CA2 . 5CC3 Cud i 0 lLL {BX�E I —l'XZ0 .riOILI 3 4i I1 - f ✓I.co t5 t UJI5-0 :t '��•-IBC �'i�G.Ca ��<_Gt=JG��S:i ter' 100 50 t.0's z t0 LO 4t EO � =--- 0.10 70 60 U. a Q8. 5G 40 C3; 1 s 0.5 5 0.5 20 EX.1:riP��': L = 200' L c00' J.J 0 - TIME OF CONCENTRATION FOR SURFACE FLOW ! I FIGURE 2 City of La Porte Intensity vs. Time of Concentration vs. Rainfall Frequency (IDF Curves) Source., Hydra 35/TP-40 100 1 i i L V 0 - C 100-year ` !f _-25-year _10-year - 5-year 3-year ji \ 2-Year 1 1 10 10o Time of Concentration, TC (minutes) I17 tr'C) 5lty, l = (d +TC)e Rainfall Frequency b d e 2-year 75-01 16.2 0.8315 3-year 77.27 17.1 0.8075 5-year 84.14 17.8 0.7881 10-year 93.53 18.9 0.7742 25-year 115.9 21.2 0.7808 100-year 125.4 21,8 0,7500 a 0 610 0. 15 0 &30 0. i 0 CURVE FOR DETERMINING STORAGE COEFFICIENT A- Ll I - Li 4 4 T_rrl Tf ._i_L A-1 4-- 4- -4 - '.F: 1 '4 j_L_ - - 14 Ij J.-j- -4-4 1 44 T7 Jr J_ r+­144- 4- . . . . . . . . . ...... L f J -1 T 4_1LI + 1-4 LJ--- L --i J_ 4_1 i + T j_p_ -4-L L--f- T"t 4 . ..... F 4 46 - - . - 1 4 (11 20 3 3 p DRAINAGE AREA (ACRES) Cs A 0 FIGURE 4 it r r r m 77 n �o m co °fit un, ra r700 / rCDr k d F-01 s a i ! Legend Streets r7 r U HCFCD Right Of Way G„ Open Channel Drainage City of La Porte Body of Water S��i CHOATE co-V kl c, t z 4 '10 associates RIGHT OF WAY MAP CITY OF LA PORTE CITY-WIDE DRAINAGE STUDY KLOTZ PRDJ. ND.: 0127. ooa. 000 EXHIBIT SCALE. 1" = 4.000' E DATE. MARCH 2008