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C> Contract #SD609AA • The original drainage design standards for subdivisions of this type were far less stringent in 1960 than they are today. The typical drainage system was designed for a 2-inchlone hour storm and stormwater retention was an unknown concept. Today's systems are designed for a minimum 10 -year storm and the retention required for storniwater treatment helps to further buffer the effects, • The capacity of the existing system has been reduced from its original design capacity by the effects of age. The System capacity has in many cases been reduced by the cffects of sedimentation and forestation. Paved streets were not required and erosion of the roadway materials into the drainage system is now a continuing. problem. Additionally, since much of the subdivision is not yet developed, many of the rear lot drainage ditches have not been maintained and are clogged with weeds, trees and trash, Six objectives relating to the improvement of water quality for Vero Lakes Estates have been established: 1) limit average discharge rates to levels acceptable to the Sebastian River Witter Control District based on agricultural land uses; (2) limit post -development peak discharge rates to pre -development peal: levels; (3) provide one inch detention for proposed paving improvements; (4) provide storage above the current water table levels where possible, rather than lowering tile water table to increase :storage capacity; (5) determine approximate design flood elevations based on accepted risk factors; and (6) increase net wetland areas(Malster 5lortnwater Management Plan for Vero Lakes Estates. 1992). IV. PROJECT DP*S 'R1lvl'ION: Vero Lakes Estates consists of 10,000 platted lots. over 2A 10 acres dating from 1956-60. The proposed site area is located approximately 9 miles inland from the Atlantic Ocean on the eastern face of what is known locally as "Tcu Mile Ridge." The site lies on the western plaits of the South Fork of the St. Sebastian River's drainage hasin. Ground elevations range from 25' to 26' NGVD along the western edge of the project arca to 19'-20' NGVD at the eastern edge of the project area. The relatively flat slope of the site contributes to the drainage problems. In 1984, COUNTY established the Vero Lakes Estates Area Municipal Service Taxing Unit (MS,ru) for the purpose of drainage and paving improvements. Within Vero L.aVes Estates, the primary surface water system consists of three large ditches, Canals A, B, and C, which are oriented cast/west and convey water to the Lateral U canal which flows northward along the eastern limits of the project area and discharges to the St. Sebastian River. The secondary surface water system consists of rear lot ditches, which discharge to the three primary canals and are oriented north/south. Street swales are the third major component of the surface water system within the project area which discharge to (lie back lot ditches and file primary canals. in addition to the canals, ditches and swales, there are several lakes and ponds within the project area. Many of these surface water bodies were constructed as borrow pits andlor recreational amenities during the initial development of the subdivision. This projcct will complete a majority of the stormwater upgrades cast of 98"' Ave. Additional block Swale work will be completed in the future_ COUNTY is currently paving the dirt roads, Page I 1 of 28