Common use of Hydrologic Studies Clause in Contracts

Hydrologic Studies. The ENGINEER shall perform a preliminary hydrologic analysis to determine the discharges for the 2-, 10-, 25-, 50-, 100-, and 500-year storm frequency events. Drainage areas delineated under 200 acres shall use the Modified Rational Area Method. Areas greater than 200 acres shall use the Soil Conservation Service (SCS) Curve Number Method or statistical analysis of stream gage data depending on available data as described in the TXDOT 2016 Hydraulic Design Manual. The ENGINEER shall complete the following subtasks:  Obtain data. The ENGINEER shall obtain existing Hydrology and Hydraulic models from drainage authorities with purview in the corridor. Other data sources shall include and are not limited to: − FEMA Flood Insurance Studies (FIS) and Flood Insurance Rate Maps (FIRMs) − Latest available terrain surface data and contour maps (from local County or TxDOT) − Land use maps − Soils maps − Historic Precipitation Data − USGS Stream gage data − Aerial imagery (latest available) − Culvert and drainage maintenance reports − Historic Flooding reports − As-built plans and data for impacted hydraulic structures DocuSign Envelope ID: 9E4E3B84-8519-409C-AEF8-0383FB0D2E89 − Design plans (calculations if available) of highway, culverts and ditches  Review FIS. The ENGINEER shall review the FEMA Flood Insurance (FIS) and Maps (FIRMs) and compare to the proposed improvements. The ENGINEER shall evaluate the potential impact to the delineated floodplain area  Determine Drainage Area Boundaries. The ENGINEER shall determine the existing conditions drainage area boundaries to be used for determining discharges for cross drainage structures, channels, and detention ponds. The delineations shall be based on the available terrain surface data, contour maps, as-built data, and aerial imagery. The ENGINEER shall conduct up to two site visits when needed to identify critical hydrologic and hydraulic areas not visible on maps. Ground survey (to be provided by the STATE) and the latest available terrain surface data and available contour maps along with current aerial imagery shall be used to identify any existing drainage features such as channels, cross drainage structures, roadways, or structures. Complete Hydrologic data/discharge calculation. Time of Concentration calculations will be performed as stated in the TxDOT Hydraulic Design Manual July 2016 edition. Calculated flows shall be compared to FEMA FIS flows and TxDOT’s Regression Analysis Equations. Hydraulic Modeling software (Hydro CAD) shall be used to calculate flows for the SCS Curve Number Method. Standard Excel spreadsheets shall be used to show the Rational Method calculations. Engineering judgement will be applied to evaluate any potential issues with existing structures. No hydraulic analysis will be performed during this study to determine existing capacity of structures  Prepare Preliminary Drainage and Hydrology Tech Memo. The ENGINEER shall present the results to the STATE in a Preliminary Drainage and Hydrology Tech Memo including supporting modeling and computations. The Preliminary Drainage and Hydrology Tech Memo shall be signed and sealed by a professional engineer.

Hydrologic Studies. The ENGINEER Engineer shall perform a preliminary hydrologic analysis to determine provide the following services: 1. Review and verify hydrology results from the schematic portion of this project. 2. Validate and update as needed the discharges for developed in the 2-, 10-, 25-, 50-, 100-schematic portion of this project 3. Verify the pre-construction and post-construction conditions developed in the schematic portion of this project in the hydrologic study. 4. Obtain the drainage area boundaries and hydrologic parameters such as impervious covered areas, and 500-year storm frequency events. Drainage areas delineated under 200 acres shall use the Modified Rational Area Method. Areas greater than 200 acres shall use the Soil Conservation Service (SCS) Curve Number Method or statistical analysis of stream gage data depending on available data as described in the TXDOT 2016 Hydraulic Design Manual. The ENGINEER shall complete the following subtasks:  Obtain data. The ENGINEER shall obtain existing Hydrology overland flow paths and Hydraulic models slopes from drainage authorities with purview in the corridor. Other data appropriate sources shall include and including, but are not limited to: − , topographic maps, GIS modeling, construction plans, and existing hydrologic studies (specifically the schematic drainage study). The Engineer shall not use existing hydrologic studies without assessing of their validity. If necessary, obtain additional information such as local rainfall from official sites such as airports. 5. Include, at a minimum, the “design” frequency and the 1% Annual Exceedance Probability (AEP) storm frequency. The report must include the full range of frequencies (50%, 20% 10%, 4%, 2%, 1%, and 0.2% AEP). 6. Compare and verify calculated discharges developed in the schematic portion of the project to the effective FEMA Flood Insurance Studies flows. If calculated discharges are to be used in the model instead of the effective FEMA flows, full justification must be documented. For each identified outfall, the Engineer shall quantify the change in peak flow rates between the existing and proposed conditions created by the project. The Engineer shall then determine if the overall increase in peak flow from the project compared to the peak flow in the receiving channel or storm drain system will create an adverse impact to the adjacent properties or existing storm drain systems. If the Engineer determines that the project will create adverse impacts to adjacent properties, the Engineer shall identify potential on-site locations for detention storage and assess potential detention storage availability. The Engineer may recommend detention structures in the form of ponds and ditches where the ROW area allows or within oversized storm drain conduits in locations with limited ROW area. Utilizing hydrograph routing software such as Hydrologic Engineering Center – Hydrologic Modeling System (FISHEC-HMS) or Storm Water Management Model (SWMM), the Engineer shall calculate required storage volumes based on hydrograph calculations and Flood Insurance Rate Maps (FIRMs) − Latest available terrain surface data and contour maps (peak flows in order to limit 100 year discharge from local County or TxDOT) − Land use maps − Soils maps − Historic Precipitation Data − USGS Stream gage data − Aerial imagery (latest available) − Culvert and drainage maintenance reports − Historic Flooding reports − As-built plans and data for impacted hydraulic structures each DocuSign Envelope ID: 9E4E3B84272D98F7-85197E9E-42C2-409CA06F-AEF8E7D2542DAFD3 Contract No. 14-0383FB0D2E89 − Design plans (calculations 7SDP5001 outfall to that produced under existing conditions. In addition, the Engineer will also assess the hydrologic impact of the project in the 2, 5, 10, 25 and 50 year storm events to the receiving system and make any recommendations for erosion protection if available) required. If the receiving system is to an existing storm sewer system outside of highwaythe State ROW, culverts the Engineer shall address impacts to the receiving storm drain system, taking into consideration what the existing system was sized to accommodate, and ditches  Review FISmake recommendations for onsite improvements as to not have an adverse impact on these systems. The ENGINEER Engineer shall review provide the FEMA Flood Insurance (FIS) following: i Preliminary calculations and Maps (FIRMs) and compare recommendation for detention design. These recommendations should be provided subsequent to the proposed improvements. The ENGINEER shall evaluate the potential impact 30% milestone submittal and prior to the delineated floodplain area  Determine Drainage Area Boundaries. The ENGINEER shall determine 60% milestone submittal in addition to a follow up meeting with the existing conditions drainage area boundaries to be used for determining discharges for cross drainage structures, channels, and detention ponds. The delineations shall be based on the available terrain surface data, contour maps, as-built data, and aerial imagery. The ENGINEER shall conduct up to two site visits when needed to identify critical hydrologic and hydraulic areas not visible on maps. Ground survey (to be provided by the STATE) State project manager and the latest available terrain surface data and available contour maps along with current aerial imagery shall be used to identify any existing drainage features such as channels, cross drainage structures, roadways, or structures. Complete Hydrologic data/discharge calculation. Time of Concentration calculations will be performed as stated in the TxDOT Hydraulic Design Manual July 2016 edition. Calculated flows shall be compared to FEMA FIS flows and TxDOT’s Regression Analysis Equations. Hydraulic Modeling software (Hydro CAD) shall be used to calculate flows for the SCS Curve Number Method. Standard Excel spreadsheets shall be used to show the Rational Method calculations. Engineering judgement will be applied to evaluate any potential issues with existing structures. No hydraulic analysis will be performed during this study to determine existing capacity of structures  Prepare Preliminary Drainage and Hydrology Tech Memo. The ENGINEER shall present the results to the STATE in a Preliminary Drainage and Hydrology Tech Memo including supporting modeling and computations. The Preliminary Drainage and Hydrology Tech Memo shall be signed and sealed by a professional engineerAustin District Hydraulics Engineer.