03-09-20 Drainage and Flooding Committee Meeting

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January 29, 2020 Mr. Lorenzo Wingate City Engineer 2963 N. 23rd Street LaPorte, TX 77571 RE: Engineering Services Fee Proposal Bayside Terrace Subdivision Drainage Improvements Revision 3 Dear Mr. Wingate: Halff Associates Inc. (Halff) is pleased to submit our proposal to provide engineering services for the Bayside Terrace Subdivision Drainage Improvements project for the City of La Porte. The purpose of the project is to increase capacity and address existing flooding issues within the subdivision by regrading roadside ditches and upsizing the existing storm sewer system. The project area is generally bounded by Pine Bluff Drive to the north, S. Broadway Street to the west, Dwire Drive to the south, and the San Jacinto Bay to the east. This proposal will address development of a preliminary engineering report (PER), final design plans, and construction phase services. Additional services include geotechnical analysis and environmental analysis. In the PER, Halff will analyze existing conditions and evaluate proposed alternatives to recommend the most feasible design based on various factors including estimated construction cost, available right-of- way and easements, constructability, conflicts with existing utilities, and inconvenience to residents. Alternatives will be presented to the City of La Porte for determination and approval of the final design. The purpose of the final design phase is to develop signed and sealed construction plans based upon findings in the PER. Existing Conditions: There are approximately 227 total structures within the "At -Risk" project area, including 206 residential homes and 21 commercial structures. All 227 structures exist within a FEMA designated Special Flood Hazard Area. Approximately 17 structures were damaged from Hurricane Harvey in 2017, resulting in over $1.1 million dollars in damages. The existing stormwater collection system is comprised of roadside ditches and underground reinforced box culvert storm sewer to convey flow to two outfall points: an underground collection system along Bayside Drive at the center of the subdivision, and a secondary collection system running along the southeastern boundary of the subdivision. Both outfalls terminate at San Jacinto Bay. Access to the southeastern collection system is limited; the system is located within fenced -in backyards of properties within the subdivision and does not exist within a utility easement nor public right-of-way. During intense rainfall events, the capacity of the southern system is exceeded, and the backwater condition inundates sections of the neighborhood upstream. 'KK: 11SNORTH, `GI1 L D ➢E"L (9361) R5616832 WJVVVH/tIfu,'W p[,;:O ditQ I_ IX /1 (:r7..J..,i"01 FAX E 6i T56... W4Z,3