Design Example Handouts. DURANGO DETENTION WORKBOOK LUNCH AND LEARN CITY OF DURANGO Meeting Date: February 7, 2017

Transcription

1 Design Example Handouts DURANGO DETENTION WORKBOOK LUNCH AND LEARN CITY OF DURANGO Meeting Date: February 7, 2017

2 Design Example 1 Residential Infill Development Durango Detention Sheet: Basin Structure Sheet Watershed Layout APPROXIMATE DRAINAGE AREA TO NORTH SAND FILTER = 0.81 ACRES APPROXIMATE WATERSHED LENGTH = 260 FEET Project Narrative: This existing 5.7 acre parcel was previously occupied by an industrial user. Approximately 1.7 acres of the parcel is going to be redeveloped into a residential townhome development. The North Sand Filter will be designed to provide water quality treatment and 100 year detention for 0.81 acres of the redevelopment site. Stage Storage Calculation North Sand Filter Stage Area Volume Stage (ft) Area (ft 2 ) Volume (ft 3 ) North Sand Filter Watershed Characteristics Description Value Units Watershed Slope ft/ft Proposed Imperviousness 66 % HSG C/D 100 % Pre Development Unit Peak Flow Rates Calculate Shape Factor : watershed flow path length (ft) total watershed area (ft 2 ) Slope Factor = overall average watershed slope (ft/ft) See Reference Sheet for soil type based Pre Development Unit Peak Flow Rates based on Shape and Slope Factors

3 Design Example 1 Residential Infill Development Durango Detention Sheet: Outlet Structure Sheet Typical Sand Filter Section View Zone 1 (WQCV) Outlet Configuration: Filter Media with Underdrain (C/D Soils) Assume 1.5 feet (minimum recommended value) Spreadsheet automatically sizes underdrain orifice to drain within specified WQCV drain time (12 hours) Typical Outlet Structure Configuration Zone 2 (EURV) Outlet Configuration: Assume Orifice Plate Assume 32 hour drain time valid solution not found Reduce to 12 hour drain time valid solution found Zone 3 (100 yr) Outlet Configuration: Weir and Pipe (w/ Restrictor Plate) Concrete Overflow Structure (weir) Designed with 7.5 feet concrete box drop inlet Outlet Pipe Assume 24 diameter pipe Assume Restrictor Plate on outlet pipe Always consider backwater from downstream system Comparison With As Design Submittal Description Durango Detention As Designed WQCV (ft 3 ) yr Detention (ft 3 ) 3, * *Note: The as designed sand filter was sized to provide volume for the WQCV only and did not specifically provide for 100 yr detention. This value is provided to show that 100 yr detention could have been incorporated into the system with little modification to the size of the sand filter.

4 Design Example 2 Mixed Use Site Development Best Management Practice: Retention Pond Durango Detention Sheet: Basin Sheet Watershed Layout APPROXIMATE DRAINAGE AREA TO POND B = 4.7 ACRES Project Narrative: This existing 18.4 acre undeveloped parcel will be converted to a mixed use site development consisting of single family lots, townhomes, multi family units, and a church site. A portion on the site, approximately 4.7 acres, will be treated with an retention pond to provide water quality treatment and 100 year detention. Pond B Watershed Characteristics Description Value Units Watershed Slope 0.05 ft/ft Proposed Imperviousness 36.6 % HSG C/D 100 % Stage Storage Calculation Use Durango Detention to Size Pond: Total Available Detention Depth = 5 ft Basin Side Slope = 3H:1V Basin Length to Width Ratio = 2:1 Pre Development Unit Peak Flow Rates APPROXIMATE WATERSHED LENGTH = 1350 FEET Calculate Shape Factor : watershed flow path length (ft) total watershed area (ft 2 ) Slope Factor = overall average watershed slope (ft/ft) See Reference Sheet for soil type based Pre Development Unit Peak Flow Rates based on Shape and Slope Factors

5 Design Example 2 Mixed Use Site Development Best Management Practice: Retention Pond Durango Detention Sheet: Outlet Structure Sheet Typical Retention Pond Section View Zone 1 (WQCV) Outlet Configuration: WQCV Orifice Plate Spreadsheet automatically sizes orifice to drain within specified WQCV drain time (12 hours) Zone 2 (EURV) Outlet Configuration: Assume Orifice Plate Assume 32 hour drain time valid solution not found Reduce to 12 hour drain time valid solution found Typical Outlet Structure Configuration Zone 3 (100 yr) Outlet Configuration: Weir and Pipe (w/ Restrictor Plate) Concrete Overflow Structure (weir) Designed with a 5 ft x 5 ft concrete box drop inlet Assume Restrictor Plate on 18 inch diameter outlet pipe Always consider backwater from downstream system Comparison With As Design Submittal Description Durango Detention As Designed WQCV (ft 3 ) 1,960 1, yr Detention (ft 3 ) 13,504 17,402* *Note: Results are not directly comparable because of the different methods used to calculated pre development peak flow rates.

6 Design Example 3 Commercial Development Durango Detention Sheet: Basin Sheet Watershed Layout APPROXIMATE DRAINAGE AREA TO SAND FILTER = 3.8 ACRES Project Narrative: This existing 5.3 acre undeveloped parcel will be developed with a hotel and associated parking lot. A portion on the site, approximately 3.8 acres, will be treated with a sand filter to provide water quality treatment and 100 year detention. Pond B Watershed Characteristics Description Value Units Watershed Slope 0.06 ft/ft Proposed Imperviousness 63.9 % HSG C/D 100 % Stage Storage Calculation Use Durango Detention to Size Sand Filter: Total Available Detention Depth = 4 ft Basin Side Slope = 4H:1V Basin Length to Width Ratio = 2:1 Pre Development Unit Peak Flow Rates APPROXIMATE WATERSHED LENGTH = 500 FEET Calculate Shape Factor : watershed flow path length (ft) total watershed area (ft 2 ) Slope Factor = overall average watershed slope (ft/ft) See Reference Sheet for soil type based Pre Development Unit Peak Flow Rates based on Shape and Slope Factors

7 Design Example 3 Commercial Development Durango Detention Sheet: Outlet Structure Sheet Typical Sand Filter Section View Zone 1 (WQCV) Outlet Configuration: Filter Media with Underdrain (C/D Soils) Underdrain is 1.5 feet below sand filter surface (minimum recommended value) Spreadsheet automatically sizes underdrain orifice to drain within specified WQCV drain time (12 hours) Typical Outlet Structure Configuration Zone 2 (EURV) Outlet Configuration: Assume Orifice Plate Assume 32 hour drain time valid solution not found Reduce to 12 hour drain time valid solution found Zone 3 (100 yr) Outlet Configuration: Weir and Pipe (w/ Restrictor Plate) Concrete Overflow Structure (weir) Designed with 3 ft x 3ft concrete box drop inlet Outlet Pipe 24 diameter pipe Assume Restrictor Plate on outlet pipe Always consider backwater from downstream system Comparison With As Design Submittal Description Durango Detention As Designed WQCV (ft 3 ) 2,307 2, yr Detention (ft 3 ) 16,465 15,461* *Note: Results are not directly comparable because of the different methods used to calculated pre development peak flow rates.