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1 1 ~l ~ 1 r j ~ 1 ~ I Section 4 Approach / methodology CSA will be responsible} along with other duties} for managing and coordinating project design} undertaking project development and plans production duties} and addressing project complexity issues. CSA has a vast experience in designing drainage systems in similar conditions as the ones encountered in the City of Sunny Isles. r , . I Drainage Analysis: After a series of field visits to the project site and reviewing similar project conditions} the following are the main critical drainage issues that have to be addressed in order to achieve an efficient drainage system under these circumstances: a) Low ground elevations: ground elevations in some areas are extremely low varying from 4 to 5 feet N.G.V.D. b) West of Collins Avenue} the percolation test results may be around E-5 to E-6 (cfs/ft2-ft of head) because of the silt/muck layers. On Collins and east of Collins} the values are good} E-3} E-4. As we approach North Bay Road} our experience indicates that below the pavement there are 3-4 feet of fill material followed by organics and silt layers down to 7 to 10 feet. Then} the sands may be found. Near the Intracoastal, these subsurface conditions worsen. As we approach Collin Avenue} the subsurface conditions get better because of the sand bar along Collins Avenue. c) Poor soil storage and infiltration capacity of the green areas due to the high groundwater elevations. d) Absence of swales} ditches} ponds} etc. making surface storage capacity for the stormwater runoff almost non-existent. Furthermore} acquiring additional right-of-way to create surface storage capacity is cost prohibited in the project area. e) A relative low well capacity ranging from 200 to 400 G.P.M. f) A combination of high groundwater stages and high tides stages are the primary reason of high water stages ~ ) r 1 I l J r t I I J : I l J L I , I l J l J . J at canals} lakes and ocean connected canals. Therefore} outfall pipes discharging into those open water surfaces are generally happening under submerge conditions} thus increasing hydraulic losses and creating flooding conditions at the streets and parking areas. g) Residents of the area are very sensible to floodings as well as other aspects such as noises and traffic interruptions. Therefore} the MOT and construction schedule should take into account these constraints in order to minimize any adverse impacts to the life of the residents living in the neighborhood of the project area. Design Approach of the Proposed Drainage System: A gravity drainage system will be design taking into account all constrains previously explained. We realized that a gravity self contained drainage system is the most desirable from the maintenance and cost prospective} but at the same time the efficiency of the system will be extremely low if we do not take into account all the factors and constrains previously mentioned. Therefore} we are proposing a drainage system that will be optimized and designed for the worst case scenario; when high ground water and hide tide stages coincide with the peak of the rainfall design event. However} depending of the hydraulic modeling output an outfall connection maybe required. Our design approach will include a hydraulic modeling using the latest version of the ICPR software that will optimize and include all the factors intervening in the stormwater runoff and we will analyze several alternatives to come up with the most efficient drainage system that address all the issues containing in the Scope of Services of the RFQ. Four different design alternatives will be analyzed and are explained as follows: Alternative 1: Design a self contained interconnected Drainage System with exfiltration trench drains. If percolation values yield low exfiltration capacity that make the exfiltration system inadequate, then a second ......