Common use of Drainage Study Clause in Contracts

Drainage Study. The Consultant will prepare, submit, and obtain approval of a Drainage Impact Analysis. This analysis will identify the changes in peak flows due to the proposed roadway improvements and recommend drainage measures to mitigate the impacts associated with the proposed improvements. This study will include the evaluation of the existing storm sewer systems and recommend preliminary size detention basin or an enlarged storm sewer system so as not to impact the receiving streams or the abutting property. The purpose of this task is to prepare a Drainage Mitigation Impact Analysis Study to determine the 100-year storm impacts resulting from construction of the project and to develop and analyze alternatives to mitigate these impacts. The following tasks describe the work to be performed:  Prepare 100-year storm drainage area maps for existing and proposed conditions, which includes the southbound lanes, within the project right of way (ROW) and any off-site areas draining into the ROW.  Compute existing and proposed peak flows with standard TxDOT methodology within the ROW. The Rational Method will be used to compute these flows for drainage areas less than 200 acres and the Small Watershed Method will be used to evaluate the impacts of the ultimate conditions. HEC- HMS modeling will be used for drainage areas equal to or greater than 200 acres.  Compute required 100-year storage volumes within the ROW using the average end area method to determine mitigation requirements for the proposed condition versus existing conditions.  Prepare existing and proposed hydrographs at each outfall location to develop mitigation alternatives to implement the required 100-year mitigation. Alternatives may include increasing storm sewer sizes beyond what is required for the design 10-year storm or improving existing roadside ditches/ or providing a detention site required within the vicinity. The location of the detention site may vary and further analysis depending on the location will be needed.  Prepare construction cost estimates for mitigation alternatives developed in the previous task to assist in selecting the most cost effective mitigation methods.  Prepare a Drainage Mitigation Study report to summarize and document the findings of this study. The report will include the following items at a minimum: o Conceptual and generic discussions of mitigation alternatives considered o Comparative costs associated with each alternative o Recommended mitigation solutions o Required mitigation volumes of ultimate versus existing conditions o Plan sheets showing the proposed mitigation plan with outfall and flowline elevations o Hydrologic and hydraulic computer models such as HEC-HMS, HEC-RAS, or XP-SWMM with drainage area maps o Drainage outfall descriptions o The report will be signed and sealed by a professional engineer.

Drainage Study. a. Hydrologic/Hydraulic Modeling (10 major channel crossings, X cross drainage structures assumed): • Prepare preliminary hydrologic and hydraulic review for the recommended alternative. The Consultant analysis will prepareinclude identification of cross drainage structure locations and preliminary sizing of structures. • Prepare schematic level hydrologic and hydraulic models or modify existing models (County’s best available data – Atlas 14 draft models, submitdrainage districts, river authorities, cities, etc.) if available, to define the drainage infrastructure required for up to 1 alignment alternative for the ultimate design schematic. Detail the methodologies employed and recommendations. The analysis will include: preparation of a preliminary design of the right of way drainage system, cross drainage structures, major channel crossings to reflect the existing and proposed conditions,recommended minimum pavement elevations based on cross drainage flood elevations for culverts; right-of-way requirements; and identify potential needs for FEMA Coordination. HEC-RAS shall be utilized for modeling all river and major channel crossings. HY-8 shall be used for non-bridge class culverts. Atlas 14 impacts will be reviewed and incorporated. Revise schematic level hydrologic and hydraulic models for the realigned preferred corridor to address property (R010404) owner’s concerns. • Regional Regression equations or another acceptable method shall be used to compute peak discharges for validation purposes and to help evaluate preliminary alignments. Once the preferred alignment is chosen, detailed hydrologic computations shall be provided based on methodologies recommended by the controlling drainage criteria manual, including technical standards from the County Atlas 14 project. • Develop existing channel cross sections based on data collection County data and readily available internet LiDAR data. • Exhibits and analysis will be prepared in the GIS environment to the extent practical. • Onsite parallel drainage for ditch and/or storm sewer sizing will only be analyzed to determine project ROW needs. Detailed inlet level calculations are not included in this scope. Revise analysis of onsite parallel ditch drainage and cross culverts for the realigned preferred corridor to address property (R010404) owner’s concerns. b. FEMA Coordination: • Coordinate with Local Floodplain Administrator as necessary throughout the project. • Determine if a CLOMR or LOMR will be required and recommended. If a CLOMR or LOMR is required after the Preliminary Drainage Report and through coordination with the Local Floodplain Administrator, a supplemental work authorization would be required. c. Impact and Mitigation Analysis: • Prepare an impact analysis to determine increases in peak flow rates for the 2,10,25, and obtain approval 100- year storm events including: existing and proposed peak flow rates, mitigation analysis, conceptual detention basin layouts, design of control structures, routing of storm hydrographs through basins. Revise impact and mitigation analysis for the realigned preferred corridor to address property (R010404) owner’s concerns. • Provide a Drainage Impact Analysiscomparison of existing versus proposed conditions at each outfall from the project area. This analysis will identify the changes in peak flows due to the proposed roadway improvements and recommend drainage • Provide measures to mitigate adverse impacts to nearby buildings, property access points and runoff patterns. • Calculate the impacts associated with the proposed improvements. This study will include the evaluation volume of the existing storm sewer systems and recommend preliminary size detention basin or an enlarged storm sewer system so as not fill to impact the receiving streams or the abutting property. The purpose of this task is to prepare a Drainage Mitigation Impact Analysis Study to determine be placed in the 100-year storm impacts resulting from construction floodplain and recommend locations for compensatory storage. d. Water Quality Analysis • Prepare a schematic level water quality analysis to determine ROW needs for accommodation of water quality treatment BMPs in accordance with TxDOT, City of Jarrell, Williamson County Sustainable Roadside Guidelines, Williamson County Subdivision Guidelines, and the TCEQ ▇▇▇▇▇▇▇ Aquifers Protection Program. Initial evaluation of the project and to develop and analyze alternatives to mitigate these impacts. The following tasks describe Corridor J alignment indicates the work to be performed:  Prepare 100-year storm drainage area maps for existing and proposed conditions, which includes the southbound lanes, eastern portion is located within the project right of way Edward’s Aquifer Recharge Zone. Revise schematic level water quality analysis the realigned corridor to address property (ROWR010404) and any off-site areas draining into the ROW.  Compute existing and proposed peak flows with standard TxDOT methodology within the ROW. The Rational Method will be used to compute these flows for owner’s concerns. e. Schematic Draft Drainage Report (Preferred Route) • Prepare a draft drainage areas less than 200 acres and the Small Watershed Method will be used to evaluate the impacts of the ultimate conditions. HEC- HMS modeling will be used for drainage areas equal to or greater than 200 acres.  Compute required 100-year storage volumes within the ROW using the average end area method to determine mitigation requirements report for the proposed condition versus existing conditions.  preferred route. f. Revised Schematic Draft Drainage Report (Revised Preferred Route to address property (R010404) owner’s concerns) • Prepare existing and proposed hydrographs at each outfall location to develop mitigation alternatives to implement the required 100-year mitigation. Alternatives may include increasing storm sewer sizes beyond what is required a draft drainage report for the design 10-year storm or improving existing roadside ditches/ or providing a detention site required within the vicinity. The location of the detention site may vary and further analysis depending on the location will be needed.  Prepare construction cost estimates for mitigation alternatives developed in the previous task preferred route to assist in selecting the most cost effective mitigation methods.  address property (R010404) owner’s concerns. g. Schematic Final Drainage Report (Preferred Route) • Prepare a final drainage report for the preferred route. `DELIVERABLES: • Schematic Draft and Final Drainage Mitigation Study report to summarize and document the findings of this study. The report will include the following items at a minimum: o Conceptual and generic discussions of mitigation alternatives considered o Comparative costs associated with each alternative o Recommended mitigation solutions o Required mitigation volumes of ultimate versus existing conditions o Plan sheets showing the proposed mitigation plan with outfall and flowline elevations o Hydrologic and hydraulic computer models such as HEC-HMS, HEC-RAS, or XP-SWMM with drainage area maps o Drainage outfall descriptions o The report will be signed and sealed by a professional engineerReport.