Drainage_and_Flooding_Report-dated_10_03_2008

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Mr. Ron Bottoms, City Manager October 1, 2008 Page 20 of 31 k I o t z associates to insufficient channel size and/or bridges and culverts which produced large hydraulic head changes at isolated locations. Inadequate Sewerage: In this situation, it is very seldom that channel overflow occurs and that therefore the source of reported flooding is unlikely due to insufficient channel capacity but rather due to the inadequacy of the sewerage (i.e., the pipes, inlets, manholes, etc.) that drains runoff waters from the problem area to the channel. Inadequacy of the sewerage could be attributed to insufficient sewer pipe sizes, numbers of storm water inlets, and/or lack of overland flow pathways. Infrequency of channel overflow is considered to occur if no channel overflow occurs for the 100-year storm eve.-tt. Mixture of Inadequate Sewerage and Insufficient Channel Capacity: This is an intermediate overflow condition for which both inadequate sewerage capacity .-and likely frequent high sewer - tailwaters occur, with both contributing to poor drainage. This condition is estimated to occur when overflow does not occur for the I 0-year storm event but does occur for the 5 0- and/or I 00-year storm event. Based upon these categories, the sources of flooding problems are identified in Table 3 in light of the estimated overflow conditions of the studied ditches and channels given in Table 2. This identification provides guidance for selection of likely needed drainage solutions to be identified in the CWDS report. Some short term flooding issues and conceptual solutions for addressing those issues have been discussed in Report 42. In addition, preliminary concepts for zddressing long term problems were identified in Reports 41 and Q. Conceptual solutions to address long term problems are described in the following: The concepts for remedy of drainage and flooding problems generally applicable to all drainage and flooding problem areas fall into the following categories: 11"Pgrade of storm sewer systems to 1) increase the capacity of a sewer line, 2) convert open ditches to sewers in streets with curb and gutter systems; and/or 3) increase the capacity of street inlets to lessen ponding in streets. To accomplish these types of upgrades, the following improvements may be done: