100-yr Design Runoff (cfs) Basin ID 103b A a B B C Totals

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Elfrieda Hart
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2 PROPOSED DEVELOPMENT The drainage for this site has been designed to be less than the maximum allowable runoff from each basin as stated in the Overall Rigden Farm drainage plan. Table 1 compares the actual runoff versus the allowable runoff from the Northwest Roads Ultimate Drainage Plan. Runoff from the four basins (A, B1, B2 and C) are to follow the intent of that plan and are to be collected in storm inlets and piped to the North Tributary Storm Sewer in Drake Road. Please refer to the attachments for the hydrologic calculations of the 10 and 100 year storm events that were performed utilizing the Rational Method. Table 1. Comparison of Flows. Rigden Farms Northwest Roads Contributing Area (Acres) 100-yr Design Runoff (cfs) Warren Federal Credit Union Subdivision 100-yr Contributing Design Area Runoff Basin ID (Acres) (cfs) Basin ID 103b A a B B C Totals b A a B1, B2, C BASIN DESCRIPTIONS The site is divided into four basins: A, B1, B2 and C. Basin A is 0.51 acres and is comprised of drainage from the roof of Lot 3 and on-site sidewalks and landscape areas. Water will flow from the roof drains into the proposed drainage system that ties into an existing stub from the existing storm system in Limon Drive. Water from the proposed sidewalk along Limon Drive will sheet flow into the curb and gutter of Limon Drive where it will then be collected by the existing inlet in Limon Drive. Basin B1 is 0.44 acres and is comprised of the eastern portion of the Tract A parking lot, on-site sidewalks and landscape areas. Water will flow into the proposed parking lot, across pervious pavers and into the proposed Type C sump inlet at design point B1. From the inlet, water will be transported via storm drain pipe to the existing storm drain system in Iowa Drive. Water from the proposed sidewalk along Iowa Drive will sheet flow into the curb and gutter of Iowa Drive where it will then be collected by the existing inlet in Iowa Drive. Basin B2 is 0.65 acres and is comprised of the western portion of the Tract A parking lot, on-site sidewalks and landscape areas. Water will flow into the proposed parking lot, across pervious pavers and into the proposed Type C sump inlet at design point B2. From the inlet, water will be transported via storm drain Page 2

3 pipe to the existing storm drain system in Iowa Drive. Water from the proposed sidewalk along Iowa Drive will sheet flow into the curb and gutter of Iowa Drive where it will then be collected by the existing inlet in Iowa Drive. Basin C is 0.40 acres and is the comprised drainage from Lots 1 and 2. It was assumed to have a percent imperviousness of 73 percent with assumed areas for roof and sidewalk. Water from Lots 1 and 2 will flow be routed into the proposed manhole at design point C. From this point water will be transported via storm drain pipe to the existing storm drain system in Iowa Drive. Please refer to the attachments for Warren Federal Credit Union Drainage Plan that depicts the drainage basins. The original design used a percent imperviousness of 90 percent. The weighted percent imperviousness of the proposed plan is calculated to be 73 percent. Therefore, the site is in substantial conformance with the previously approved Final Drainage Reports. Hydraulic calculations for sizing the proposed stormwater inlets and pipe discussed in Basins A, B1, B2 and C have been completed using area inlet spreadsheets and StormCAD hydraulic modeling software. Calculations are attached and show that the storm systems in Iowa and Limon Drives have capacity. FOUR STEP LOW IMPACT DEVELOPMENT PROCESS With the development of the site, the design team has followed the four step low impact development process outlined in Urban Drainage. Water quality is required for the site and is provided by an existing off-site water quality and detention pond. In addition to water quality, Low Impact Development (LID) criteria must be met. It is required that no less than fifty percent of any newly added impervious area must be treated using one or a combination of LID techniques. For Lots 1, 2, 3 and Tract A, 51% of newly added impervious area is treated by pervious pavers LID technique. It is also required that no less than twenty five percent of any newly added pavement areas must be treated using a permeable pavement technology. For Lots 1, 2, 3 and Tract A, 25% of newly added pavement is pervious pavers. Please refer to the attachments for LID calculations. Please note, calculation includes assumed roof and sidewalk area for Lots 1 and 2. Page 3

4 Table 2. LID Compliance. An erosion control plan will be implemented during construction that will address source control and unwanted materials (hazardous materials, sediment) from entering the downstream storm systems. The contractor will be responsible for implementing the erosion control plan and adequately addressing any spills or clean up on site. The proposed redevelopment has improved upon the existing conditions by providing off site water quality and detention and onsite LID treatment. The site has been designed with provisions for safe and efficient control of stormwater runoff in a manner that will not adversely affect the downstream storm system and will improve water quality. Overall, it is evident that the proposed redevelopment will have a positive impact on the overall stormwater management system. Page 4

5 STANDARD OPERATING PROCEDURES Pervious Pavers Maintenance Plan Routine Maintenance Table (Summary from Chapter 6 of UDFCD) Required Action Maintenance Objective Frequency of Action Debris Removal, Sweeping, and Vacuuming Remove debris with regular sweeping of the pavement surface, typically performed with a broom sweeper. Removing solids from void spaces will require a vacuum or regenerative air Sweeper. Routine Sweeping should be performed weekly to monthly depending on the season. Frequency of vacuuming is site specific but recommended twice annually to maintain infiltration rates. Snow Removal Full or Partial Replacement of Pavement or Infill Material Inspections Conventional plowing operations should be used for snow removal. Do not use sand or deicing liquids on permeable pavement systems. If sand is accidentally used, use a vacuum sweeper to remove it Concrete pavers, when installed correctly, should have a long service life. Follow industry guidelines for installation and replacement after underground repairs. If the surface is completely clogged, restoration of infiltration can be achieved by removing the first ½ to 1 inch of soiled aggregate infill material with a vacuum sweeper. Replace with clean aggregate infill material using a push broom. Inspect to ensure that the facility continues to function as initially intended. Non-routine Performed as needed after winter storm events. Non-routine Performed as needed when surface infiltration becomes completely clogged or when individual pavers require a repair. Routine Inspect pavement condition at least annually, either during a rain event or with a garden hose to ensure that water infiltrates into the surface. Systematic measurement of surface infiltration can be accomplished using ASTM C1701 Standard Test Method for Infiltration Rate of In Place Pervious Concrete Page 5

6 Storm Drain Lines Maintenance Plan Routine Maintenance Table Required Action Maintenance Objective Frequency of Action Debris Removal from Inlets and Catch Basins Debris Removal from Storm Pipes Inspection Remove debris and trash from inlets to prevent them from continuing downstream or clogging and reducing the flow capacity of the system. Ensure the pipe systems function as intended. Reduced capacities in the pipes will cause the system to back up and increase the frequency of surface flooding that could damage property. Use a video camera to inspect the condition of the storm drain pipes looking for sediment buildup and structural integrity. Clean out pipes as needed. If the integrity of the pipe is compromised, then repair the damaged section(s). Non-routine Remove debris as needed after storm events or seasonally such as during the Fall with heavy amounts of leaves and twigs entering the system. Non-routine Pipe cleaning is recommended as needed based on the results of inspections or when the system is no longer able to regularly convey routine storm flows from the site. Routine Visually Inspect pipes and inlets at least annually or after major storm events. Every 2-5 years the pipes should be inspected with a video camera. If you have any questions or comments please contact me at (970) Sincerely, Michael Oberlander, P.E., LEED AP Colorado Professional Engineer Attachments Page 6

9 SUMMARY DRAINAGE SUMMARY TABLE Design Tributary Area C (10) C (100) tc (10) tc (100) Q(10)tot Q(100)tot Sub-basin Point (ac) (min) (min) (cfs) (cfs) 10 and 100 year storm a A Existing Storm System in Limon Drive b1 B Type C Sump Inlet b2 B Type C Sump Inlet c C Existing Storm System in Illinois Drive Page 1

10 Interwest Consulting Group LOCATION: Warren Federal Credit Union PROJECT NO: COMPUTATIONS BY: es DATE: 11/3/2015 RUNOFF COEFFICIENTS & % IMPERVIOUS Recommended Runoff Coefficients from Table RO-11 of City of Fort Collins Stormwater Code, Volume I Recommended % Impervious from Table RO-3 Urban Storm Drainage Criteria Manual, Volume I Type B Soils Runoff % coefficient Impervious C Streets, parking lots (asphalt): Sidewalks (concrete): Roofs: Gravel or Pavers: Landscape Areas (Flat, Sandy) : Landscape Areas (Steep, Sandy) : SUBBASIN TOTAL TOTAL ROOF PAVED PAVERS SIDEWALK LANDSCAPE RUNOFF % DESIGNATION AREA AREA AREA AREA AREA AREA AREA COEFF. Impervious REMARKS (ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C) A ,350 12, ,925 3, B , ,977 2, , B , ,977 5,427 4,590 4, C ,318 13, ,000 3, Assmumption for Future TOTAL ,230 25,959 24,954 8,255 12,447 15, Equations - Calculated C coefficients & % Impervious are area weighted C = Σ (Ci Ai) / At Ci = runoff coefficient for specific area, Ai Ai = areas of surface with runoff coefficient of Ci n = number of different surfaces to consider At = total area over which C is applicable; the sum of all Ai's FC FLOW.xls

11 Interwest Consulting Group LOCATION: Warren Federal Credit Union PROJECT NO: COMPUTATIONS BY: es DATE: 11/3/2015 STANDARD FORM SF-2 TIME OF CONCENTRATION - 2 and 10 YR 2 and 10-yr storm Cf = 1.00 from Table RO-12 of City of Fort Collins Stormwater Code, Volume I SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS DATA TIME (ti) (tt) (URBANIZED BASIN) tc DESIGN SUBBASIN(s) Area C Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10 PONIT (ac) (%) (min) (%) Manning (ft/s) (min) ti + tt (min) (min) (1) (2) (3) (4) (5) (6) (7) (8) rough. (9) (10) (11) (12) (13) (14) a A b1 B b2 B c C EQUATIONS: tc = ti + tt ti = [1.87 (1.1 - CC f ) L 0.5 ] / S 1/3 tt = L/Vel. Velocity from Manning's Equation with R=0.1 (corresponds to Figure 3-3 of City of Fort Collins Design Manual) final tc = minimum of ti + tt and urbanized basin check min. tc = 5 min. due to limits of IDF curves FC FLOW.xls

12 Interwest Consulting Group LOCATION: Warren Federal Credit Union PROJECT NO: COMPUTATIONS BY: es DATE: 11/3/2015 STANDARD FORM SF-2 TIME OF CONCENTRATION YR 100-yr storm Cf = 1.25 from Table RO-12 of City of Fort Collins Stormwater Code, Volume I SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS DATA TIME (ti) (tt) (URBANIZED BASIN) tc DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10 PONIT (ac) (%) (min) (%) Manning (ft/s) (min) ti + tt (min) (min) (1) (2) (3) (4) (5) (6) (7) (8) rough. (9) (10) (11) (12) (13) (14) A A b1 B b2 B C C EQUATIONS: tc = ti + tt ti = [1.87 (1.1 - CC f ) L 0.5 ] / S 1/3 tt = L/Vel. Velocity from Manning's Equation with R=0.1 (corresponds to Figure 3-3 of City of Fort Collins Design Manual) final tc = minimum of ti + tt and urbanized basin check min. tc = 5 min. due to limits of IDF curves FC FLOW.xls

13 Interwest Consulting Group LOCATION: Warren Federal Credit Union PROJECT NO: COMPUTATIONS BY: es DATE: 11/3/ yr storm, Cf = 1.00 RATIONAL METHOD PEAK RUNOFF (City of Fort Collins, 2-Yr Storm) DIRECT RUNOFF CARRY OVER TOTAL REMARKS Design Tributary A C Cf tc i Q (2) from Q (2) Q(2)tot Sub-basin Design Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) A A B1 B B2 B C C Q = C f C ia Q = peak discharge (cfs) C = runoff coefficient C f = frequency adjustment factor i = rainfall intensity (in/hr) from City of Fort Collins IDF curve (4/16/99) A = drainage area (acres) i = / (10+ tc) FC FLOW.xls

14 Interwest Consulting Group LOCATION: Warren Federal Credit Union PROJECT NO: COMPUTATIONS BY: es DATE: 11/3/ yr storm, Cf = 1.00 RATIONAL METHOD PEAK RUNOFF (City of Fort Collins, 10-Yr Storm) DIRECT RUNOFF CARRY OVER TOTAL REMARKS Design Tributary A C Cf tc i Q (10) from Q (10) Q(10)tot Sub-basin Design Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) A A B1 B B2 B C C Q = C f C ia Q = peak discharge (cfs) C = runoff coefficient C f = frequency adjustment factor i = rainfall intensity (in/hr) from City of Fort Collins IDF curve (4/16/99) A = drainage area (acres) i = / (10+ tc) FC FLOW.xls

15 Interwest Consulting Group LOCATION: Warren Federal Credit Union PROJECT NO: COMPUTATIONS BY: es DATE: 11/3/ yr storm, Cf = 1.25 RATIONAL METHOD PEAK RUNOFF (City of Fort Collins, 100-Yr Storm) DIRECT RUNOFF CARRY OVER TOTAL REMARKS Des. Area A C Cf tc i Q (100) from Q (100) Q(100)tot Design Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) A A B1 B B2 B C C Q = C ia Q = peak discharge (cfs) C = runoff coefficient i = rainfall intensity (in/hr) from City of Fort Collins IDF curve (4/16/99) A = drainage area (acres) i = / (10+ tc) FC FLOW.xls

19 Conduit FlexTable: Combined Pipe/Node Report Label P1 P2 P3 Start Node EX INLET IN IOWA B1 B2 Energy Grade Line (Out) Stop Node B1 B2 C Length (Unified) Material Concret e Concret e Concret e Diameter (in) Flow (cfs) Velocity (ft/s) Invert (Start) Invert (Stop) Slope (Calculated) (ft/ft) Hydraulic Grade Line (In) Hydraulic Grade Line (Out) Energy Grade Line (In) Storm B.stsw 2/23/2016 Bentley Systems, Inc. Haestad Methods Solution Center 27 Siemon Company Drive Suite 200 W Watertown, CT USA Bentley StormCAD V8i (SELECTseries 3) [ ] Page 1 of 1

20 FlexTable: Catch Basin Table ID Label B1 B2 C Elevation (Ground) Elevation (Rim) Elevation (Invert) Flow (Additional Carryover) (cfs) Hydraulic Grade Line (In) Hydraulic Grade Line (Out) Energy Grade Line (In) Energy Grade Line (Out) Storm B.stsw 2/23/2016 Bentley Systems, Inc. Haestad Methods Solution Center 27 Siemon Company Drive Suite 200 W Watertown, CT USA Bentley StormCAD V8i (SELECTseries 3) [ ] Page 1 of 1

21 FlexTable: Outfall Table Label EX INLET IN IOWA Elevation (Ground) Set Rim to Ground Elevation? False Elevation (Invert) Elevation (User Defined Tailwater) Hydraulic Grade Flow (Total Out) (cfs) Energy Grade Line Storm B.stsw 2/23/2016 Bentley Systems, Inc. Haestad Methods Solution Center 27 Siemon Company Drive Suite 200 W Watertown, CT USA Bentley StormCAD V8i (SELECTseries 3) [ ] Page 1 of 1

22 Profile Report Engineering Profile - Profile - 1 (Storm B.stsw) Storm B.stsw 2/23/2016 Bentley Systems, Inc. Haestad Methods Solution Center 27 Siemon Company Drive Suite 200 W Watertown, CT USA Bentley StormCAD V8i (SELECTseries 3) [ ] Page 1 of 1

24 Conduit FlexTable: Combined Pipe/Node Report Label P1 P2 P3 Start Node EX MH IN LIMON MH-2 MH-1 Energy Grade Line (Out) Stop Node MH-2 MH-1 A Length (Unified) Material Concret e PVC PVC Diameter (in) Flow (cfs) Velocity (ft/s) Invert (Start) Invert (Stop) Slope (Calculated) (ft/ft) Hydraulic Grade Line (In) Hydraulic Grade Line (Out) Energy Grade Line (In) Storm A.stsw 2/17/2016 Bentley Systems, Inc. Haestad Methods Solution Center 27 Siemon Company Drive Suite 200 W Watertown, CT USA Bentley StormCAD V8i (SELECTseries 3) [ ] Page 1 of 1

25 FlexTable: Catch Basin Table ID 30 A Label Elevation (Ground) Elevation (Rim) Elevation (Invert) Flow (Additional Carryover) (cfs) 5.10 Hydraulic Grade Line (In) Hydraulic Grade Line (Out) Energy Grade Line (In) Energy Grade Line (Out) Storm A.stsw 2/17/2016 Bentley Systems, Inc. Haestad Methods Solution Center 27 Siemon Company Drive Suite 200 W Watertown, CT USA Bentley StormCAD V8i (SELECTseries 3) [ ] Page 1 of 1

26 FlexTable: Manhole Table MH-1 MH-2 Label Elevation (Ground) Elevation (Rim) Bolted Cover? False False Elevation (Invert) Flow (Total Out) (cfs) Hydraulic Grade Line (Out) Hydraulic Grade Line (In) Energy Grade Line (In) Energy Grade Line (Out) Storm A.stsw 2/17/2016 Bentley Systems, Inc. Haestad Methods Solution Center 27 Siemon Company Drive Suite 200 W Watertown, CT USA Bentley StormCAD V8i (SELECTseries 3) [ ] Page 1 of 1

27 FlexTable: Outfall Table Label EX MH IN LIMON Elevation (Ground) Set Rim to Ground Elevation? True Elevation (Invert) Elevation (User Defined Tailwater) Hydraulic Grade Flow (Total Out) (cfs) 5.10 Energy Grade Line Storm A.stsw 2/17/2016 Bentley Systems, Inc. Haestad Methods Solution Center 27 Siemon Company Drive Suite 200 W Watertown, CT USA Bentley StormCAD V8i (SELECTseries 3) [ ] Page 1 of 1

28 Profile Report Engineering Profile - Profile - 1 (Storm A.stsw) Storm A.stsw 2/17/2016 Bentley Systems, Inc. Haestad Methods Solution Center 27 Siemon Company Drive Suite 200 W Watertown, CT USA Bentley StormCAD V8i (SELECTseries 3) [ ] Page 1 of 1

32 LID Table 50% On-Site Treatment by LID Requirement New Impervious Area 60,266 acre/sq. ft. Required Minimum Impervious Area to be Treated 30,133 acre/sq. ft. Ratio Area of Paver Section #1(Basin B1) 2,828 acre/sq. ft. Pavement area for Paver Section #1(up to 3:1 is permited) 10,977 acre/sq. ft. 3.9 Impervious Area Treated by LID Treatment Method #1(Pervious Pavement System) 11,910 acre/sq. ft. 4.2 Area of Paver Section #2(Basin B2) 5,427 acre/sq. ft. Pavement area for Paver Section #2(up to 3:1 is permited) 13,977 acre/sq. ft. 2.6 Impervious Area Treated by LID Treatment Method #1(Pervious Pavement System) 18,567 acre/sq. ft. 3.4 Total Impervious Area Treated 30,477 acre/sq. ft. Actual % On-Site Treated by LID 51 % 25% Porous Pavement Requirement New Pavement Area 33,209 acre/sq. ft. Required Minimum Area of Porous Pavement 8,302 acre/sq. ft. Area of Paver Section #1 2,828 acre/sq. ft. Area of Paver Section #2 5,427 acre/sq. ft. Total Porous Pavement Area 8,255 acre/sq. ft. Actual % of Porous Pavement Provided 25 %

33 LID Table 50% On-Site Treatment by LID Requirement New Impervious Area 60,266 acre/sq. ft. Required Minimum Impervious Area to be Treated 30,133 acre/sq. ft. Ratio Area of Paver Section #1(Basin B1) 2,828 acre/sq. ft. Pavement area for Paver Section #1(up to 3:1 is permited) 10,977 acre/sq. ft. 3.9 Impervious Area Treated by LID Treatment Method #1(Pervious Pavement System) 11,910 acre/sq. ft. 4.2 Area of Paver Section #2(Basin B2) 5,427 acre/sq. ft. Pavement area for Paver Section #2(up to 3:1 is permited) 13,977 acre/sq. ft. 2.6 Impervious Area Treated by LID Treatment Method #1(Pervious Pavement System) 18,567 acre/sq. ft. 3.4 Total Impervious Area Treated 30,477 acre/sq. ft. Actual % On-Site Treated by LID 51 % 25% Porous Pavement Requirement New Pavement Area 33,209 acre/sq. ft. Required Minimum Area of Porous Pavement 8,302 acre/sq. ft. Area of Paver Section #1 2,828 acre/sq. ft. Area of Paver Section #2 5,427 acre/sq. ft. Total Porous Pavement Area 8,255 acre/sq. ft. Actual % of Porous Pavement Provided 25 %