Common use of Hydrologic Studies Clause in Contracts

Hydrologic Studies. The Engineer shall conduct hydrologic analysis for the limits of project roadway, the contributing drainage area to the roadway and cross drainage structures that includes four outfalls. This analysis shall incorporate a thorough evaluation of the methodology available, comparison of the results of two or more methods, and calibration of results against measured data. The analysis shall consider the pre- construction (existing) and post-construction (proposed) conditions. Specific scope of work includes the following: 1. Delineate existing conditions drainage area boundaries for the approximately 0.79 miles of road- way Right of Way (ROW) and contributing drainage areas to the existing three cross drainage structures. This includes delineation of drainage areas to each crossing / outfall as well as further delineation of sub-drainage areas specific to each existing and proposed ditch / storm sewer. Ex-isting hydrologic studies will not be used without Engineer’s assessment of validity. 2. Determine existing conditions hydrologic parameters such as impervious covered areas, overland flow paths and slopes from appropriate sources including but not limited to topographic maps, GIS modeling, the National Land Cover Dataset (NLCD), and construction plans and existing hydrologic studies. Hydrologic parameters will be calculated for approximately 0.79 miles of existing roadway ROW and contributing drainage area to the three cross drainage structures. This includes the larger drainage areas to each crossing / outfall as well as sub- drainage areas specific to each existing and proposed ditch / storm sewer. 3. Update the available hydrologic studies with Atlas 14 rainfall. 4. Calculate existing conditions discharges using appropriate hydrologic methods. Include at a minimum, the “design” frequency to be specified by the State and the 1% Annual Exceedance Probability (AEP) storm frequency. It may be required to include the full range of frequencies (50%, 20%, 10%, 4%, 2%, 1%, and 0.2% AEP). This includes development of both peak flows and full hydrographs. 5. Delineate proposed conditions drainage area boundaries for the proposed approximately 0.79 miles of roadway ROW and contributing drainage areas to the proposed three cross drainage structures. This includes delineation of drainage areas to each crossing / outfall as well as further delineation of sub-drainage areas specific to each existing and proposed ditch / storm sewer. 6. Determine proposed conditions hydrologic parameters such as impervious covered areas, overland flow paths and slopes from appropriate sources including but not limited to topographic maps, GIS modeling, and construction plans and existing hydrologic studies. Hydrologic parameters will be calculated for the approximately 0.79 miles of proposed roadway ROW and contributing drainage area to the three cross drainage structures. 7. Calculate proposed conditions discharges using appropriate hydrologic methods. Include at a minimum, the “design” frequency to be specified by the State and the 1% AEP storm frequency. It may be required to include the full range of frequencies (50%, 20%, 10%, 4%, 2%, 1%, and 0.2% AEP). This includes development of both peak flows and full hydrographs.