PSA - McCormick Engineering - Southfield Lake Drainage Study

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Understanding of the Assignment McCormick Engineering, LLC (MEL) recently performed a hydrologic analysis of the Phillips Ditch watershed, which includes the areas that are tributary to Southfield Lake and portions of Miami Road. The scope of the study will include a review on the adequacy of Southfield Lake to offset current and future levels of development within the Southfield Subdivision, as well as an estimation of impacts to downstream receiving streams as a result of the City Miami Street widening project constructed circa 2010. Specific flood control options will be investigated to address adverse impacts as noted below. The greater Phillips Ditch watershed associated with the previous hydrologic analysis is shown in the attached Figures 1-3. The portion of the watershed undercurrent consideration is related to development within the portions of the watershed identified as Miamil and SField2 in Figure 3. The study will focus on a realistic analysis of extreme rainfall events for: existing conditions; estimation of Miami widening impacts; estimation of watershed with fully developed Southfield Development. Scope of Services MEL will perform the following tasks in order to complete the noted study. Task 1— Review of Previous Studies This task will include collection of available data and documents from the City related to the construction of the Southfield Lake and the Miami Road widening project. This data includes, but is not limited to, the Southfield Lake drainage study report by others, information from historical records, topographic mapping, and the 2016 engineering study of the Greater Phillips Ditch watershed. Task 2 — Field Reconnaissance MEL engineers will conduct a field reconnaissance of the targeted portion of the watershed. This will include site visits to confirm and enhance hydrologic analysis performed in the 2016 engineering study. Task 3 — Hydrologic Modeling MEL stall will enhance the previously developed HEC-HMS hydrologic model of the Phillips Ditch Watershed for the Miami Road widening impacts, as well as the Southfield Lake current and planned development. This hydrologic analysis shall be based upon the predicted watershed response to the following precipitation events utilized in the previous 2016 MEL study: • 100-year, 6 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) • 100-year, 12 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) • 100-year, 24 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) • 100-year, 96 hr precipitation event (NOAA Atlas 14 rainfall depth/distribution) Southfield Lake Hydrologic Study Study and Report Phase - Scope of Services Page 13 of 17 (Exhibit A- Engineer's Services)