19 - Drainage Presentation - Sandy Creek Upper Tributaries 4 and 6

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for residential areas, Class I & 2, ten-year cycle for apartment areas and mass housing projects, and twenty -five-year cycle for areas of lower zoning classification than residential. No street shall be designed or allowed in any subdivision to carry more surface water than can be carried by the street when the water is running curb deep. All drainage easements over or across adjacent tracts of land that are necessitated by the subdividing of a tract of land shall be secured and furnished to the City by the subdivider. " The City Engineering Department would recommend an overhaul of this section to be included in the Paris Development Code as it is developed. I would recommend that our Code of Ordinance base most zoning at a minimum of the 50 year recurrence interval storm to store more water onsite before discharging downstream. Requiring a larger recurrence interval storm (I.E. 100 year) for each development would be better, but may prove cost prohibitive. Requiring stormwater detention and a slower discharge rate would help in any rain event because there would be metering of water off the site, as opposed to now where in many cases, there is no flood storage whatsoever. I also highly recommend �.,etting away from automatically draining all of the stormwater to the public streets. Enclosing the stormwater into sufficiently sized pipes after their private detention facility, and draining directly to an established and appropriately sized tributary would be the best option. I believe strong, two-way communication with private developers and detailed and enforceable maintenance plans for private drainage facilities will be important moving forward. I discussed some of these issues with the City of Sherman, Texas, and they have the following statement in their Stormwater Manual, "A detention facility must be able to hold a 100 year (2 hour rainfall event) for the site without exceeding the pre -developed Discharge Rate. " The City of McKinney also requires the 100 year event to be detained. Since our current requirement is not defined in clear terms like Sherman and McKinney, I believe 50 year storm detention and discharge is a reasonable requirement. Each site is different, and an individually engineered solution needs to be evaluated each time. As we move forward, the City Engineering Department will emphasize with each engineer working on these projects that this is of utmost importance to the city. Regarding #6: The Engineering Department would like to conduct an aerial survey of the entire city to enhance understanding of existing drainage pathways. Lidar stands for Laser imaging, detection, and ranging. This would be conducted by a plane flight, with a laser shooting every surface throughout the city at 4-8 shots per square meter. This will help immensely as we look to improve drainage capacity, understand flowpaths, revise floodplains, measure existing impervious areas (e.g. rooftops, sidewalks, streets), etc. Prices include flights and data processing. Once processed, we will have 1 foot contours throughout the city, and that will reduce survey costs for individuals wanting to develop in Paris (or any users of the Platting process). The data would also be ready and available for special consultants and will reduce the need for special surveys. Costs for this work to be conducted is approximately $34,000. c