oil gas drainage task force meeting - weldgov.com
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Oil & Gas Drainage Task Force Meeting02/28/2020
Drainage Calculation Process1. Site Information/Basin Delineation
2. Rainfall
3. Runoff Calculations
4. Detention
5. Culverts/Open Channels
Weld County Preferred Formulas and Calculations• Runoffo Rational Methodo 2007 UD Runoff Coefficientso UD Rational v1.02a
• Detention oModified FAA Methodo UD Detention v2.35
Rainfall Intensity
Source: USDCM 2004 (same as current edition)
Time of Concentration
Source: USDCM 2007 (same as current edition)
Time of Concentration (Overland/Initial)
Source: USDCM 2007 (same as current edition)
• Max length for rural = 500 feet• Max length for urban = 300 feet
Time of Concentration (Channelized)
Source: USDCM 2007 (same as current edition)
Time of Concentration (Channelized)
Source: USDCM 2018 (same as 2007 edition)
Time of Concentration (Urban Check)
Source: USDCM 2007
Only to be used in urbanized growth areas or urban areas
Runoff Coefficients, C
Source: USDCM 2007
Runoff Coefficients, C
Source: USDCM 2007
Runoff Coefficients, C
Source: USDCM 2007
Runoff Coefficients, C
Source: USDCM 2007
Runoff Coefficients, C
Source: USDCM 2007
Detention
Source: USDCM 2011
Detention
Source: USDCM 2011
Detention
Source: USDCM 2011
Detention
Source: USDCM 2011
Culverts and Open Channels• Culverts
o HY‐8o Culvert Master
• Open Channels o Flowmastero AutoCAD
Calculations
Code Change Recommendations• Allow detention pond area to be calculated at 2% imperviousness (Policy Change)
• Allow alterative materials for the emergency spillway cutoff wall (Chapter 21)
• Allow retention ponds without a variance only for the construction phase (Chapter 21)
• Consider less than 1 foot of freeboard only for the construction phase (Chapter 21)
• Allow secondary containment areas to be subtracted from site imperviousness calculations (Chapter 21)
• NEW: Define the construction phase for oil and gas developments (Chapter 21)
• NEW: Allow a 5 cfs release rate only during the construction phase, production phase is still held to Chapter 8 requirements (Chapter 21)
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