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HomeMy WebLinkAbout1994 City Engineer LetterCity of Sebastian 1225 MAIN STREET 0 SEBASTIAN, FLORIDA 32958 TELEPHONE (407) 589-5330 0 FAX (407) 589-5570 May 4, 1994 Blanche Soucheck, Hydrologist Resource Management Department St. Johns River Water Management District Melbourne Field Office 305 East Drive Melbourne, F1 32904 RE: Consumptive Use.Permit Application No. 2-061-0152 ANGRF Dear Blanche: I have received your letter dated May 2nd, 1994. In response to your first question, the orifice invert elevation of 15.5 was proposed to reduce pollutant loading from storm water runoff from the Golf Course. Initially it was my understanding that the consumptive use permit would require that the lake system not be kept artificially full by the existing well. It was my understanding that the district was concerned about pollutants discharging from the golf course. That is if the lakes were kept artificially full, then the pollutants entering the lake would exit the system without any. treatment. The District requested that a 25 year storm event be analyzed for the golf course to determine the elevation that would retain the runoff, to assure treatment. A staging rod would identify the level of the lake that no additional filling of the lake would take place. Considering the districts' objective to reduce pollutant loading. I considered the installation of the orifice at elevation 15.5 to reduce stormwater pollutant loading for all weather conditions. I emphasize all weather conditions, because the orifice will help to reduce pollutant loading during the rainy seasons whereas the culvert outfall from the system will not. To understand why this is true consider two separate weather conditions. 1. Rainy or wet conditions 2. Dry or parched conditions. Considering the rainy or wet conditions, the existing culvert pipe is set at elevation 16 which will establish the water level. Then when a moderate rainstorm occurs, the storm surge would pass immediately through the culvert pipe into the receiving drainage ditch carrying the pollutants. This is because, there was no storage volume to prevent that surge of stormwater from passing directly out through the culvert pipe. If an orifice is constructed, as part of the outfall system, then the storage volume would be available to halt the surge. The orifice would then allow a gradual discharge of the lake allowing the pollutants to settle out. Considering the dry season, both systems function identically. The maximum level at which the lake can be filled would be elevation 15.5. Instead of a range rod being located in the lake, the maintenance supervisor would be able to determine the maximum filling level of the lake once it reached the orifice level without discharging. Now, in either case, should a moderate storm event occur, this storm surge entering the lake would be impeded by the storage volume available which occurs between elevation 15.5 and 16.0. I discussed this matter with Perry Jennings on the premise that it was beneficial to the district in reducing the stormwater pollutant loading. He understood the method to my madness, but pointed out from the hydrologists point of view that the orifice would be negatively affecting the groundwater table. So what might be good from a pollution reduction standpoint would not necessarily be beneficial from the hydrologists point of view. Continuing with the thought of impacts to groundwater, one needs to consider both weather conditions which are as identified above. During the wet season the ground is typically saturated from continual rainfalls and the groundwater elevation is extremely high which moves laterally to the lakes. The orifice will not drastically affect the average high groundwater table. Because the lateral movement of groundwater through the soil is a function of the hydraulic head and the soil conditions. This is a gradual process, the ground enters the lake system at the same rate it exits the orifice, providing a steady state system. Under dry conditions, the ground becomes significantly parched. Most of the groundwater recovery will occur as the moisture is taken up into the soil before it reaches the lake. In other words, most of the rainfall will be recharged into the ground where the rainfall event occurred and not because the lake system will be recharging the groundwater. In conclusion, I felt that the orifice would be a benefit to the district in obtaining their objectives. However, if the district feels that other objectives are being compromised, then I would be more than satisfied to eliminate the orifice and allow the discharge to occur through the culvert pipe. I believe that it was my responsibility to consider the best alternative to reach the districts objective. In response to the second question of your letter dated May 2nd, 1994, the number of seats located inside of the club house is 60. If you have any questions or need additional information, please do not hesitate to contact me at this office. Sincerely, i Daniel C. Eckis, P.E. City Engineer/Public Works Director DCE:lk cc: City Manager / Chris McCarthy, Golf Course Superintendent t/