Red Barn R.V. and Boat Storage Weld County, Colorado. Final Drainage Report

Transcription

1 Red Barn R.V. and Boat Storage Weld County, Colorado Final Drainage Report Prepared for Kevin Moore Project No February 27, 2017 Prepared By: KETTERLING, BUTHERUS AND NORTON ENGINEERS, LLC th Street Greeley, CO 80631

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4 Table of Contents I. General Location & Description... 1 A. Location... 1 B. Description of Property... 1 C. Drainage Design Concept... 1 II. Drainage Basins and Sub-basins... 2 A. Major Basin Description... 2 A.1 On-Site Flows... 2 A.1 Off-Site Flows... 2 B. Sub-basin Description... 2 III. Drainage Design Criteria... 2 A. Regulations... 2 B. Development Criteria Reference and Constraints... 3 C. Hydrological Criteria... 3 D. Hydraulic Criteria... 3 E. Waiver/Variance from Criteria... 3 F. Stormwater Quality Considerations... 3 IV. Wetland Preservation & Mitigation... 4 V. Drainage Facility Design... 4 A. General Concept... 4 B. Specific Details... 4 VI. Conclusions... 5 A. Compliance with Standards... 5 B. Drainage Concept... 5 VII. References... 5 VIII. Appendices Appendix A - Calculations 6-44 Appendix B - Charts, Graphs & References Appendix C - Drawing in Pocket 58 Drainage Exhibit

5 I. General Location & Description A. Location The Red Barn R.V. and Boat Storage facility project is located in unincorporated Weld County, directly east of Timnath Reservoir. More particularly, it is located the Southwest Quarter of Section 19, Township 7 North, Range 67 West of the 6 th Principal Meridian, County of Weld, State of Colorado. The land generally slopes from northwest to southeast. The property is bounded by Weld County Road 13 (Larimer County Road 1) to the west, and existing rural residential lots on the remaining three sides. Directly west across the county road is the entrance to the Wildwing Subdivision (see Appendix A, Page 8 for vicinity map). The existing house on the property is currently served by cel Energy and the North Weld County Water District. There is no telephone or cable service at present, gas is delivered to an onsite propane tank and an individual onsite waste treatment (septic) system handles sanitary flows. B. Description of Property Red Barn R.V. and Boat Storage property encompasses a total area of approximately 10.0 acres of land that has historically been used as a single-family residence with outbuildings and grassed meadow with an average slope of 1.2% to the southeast. The site also includes an irrigation ditch along the northern property line and other small irrigation appurtenances that were used to flood irrigate the meadow area. Improvements to the site will include the removal of certain outbuildings and paved concrete areas, addition of a screening fence, grading for proper drainage and resurfacing of the proposed storage area with recycled asphalt. All improvements to the site shall happen during the same phase of construction. C. Drainage Design Concept Upon investigation it was found that the site is located in an unincorporated part of Weld County and found on the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) panel 08123C1200E, which is a non-printed map panel. According to the FEMA Weld County Index Map 08123CIND0A, effective January 20, 2016, the non- printed panel 08123C1200E is an area where no special flood hazards were identified. The site has the historic basins that have been designated HA, HB and HC. Historic Basin HA drains to the southeast of the site and encompasses the majority of the property, with a measurement of 9.11 acres. Historic Basin HB includes the western 0.61 acre portion of the property along the county road and drains south in the roadside swale. Historic Basin HC incorporates 0.28 acres of irrigation ditch along the northern site boundary and will drain east along the ditch flowline. Developed basins DA, DB and DC were delineated to maintain the same boundaries as the historic basins. The proposed grading shows DA draining to a detention pond in the southeast corner of the property, while DB and DC will continue to drain along their historic paths. The onsite detention pond, named Detention Pond A, has been sized to adequately store the developed flow from Basin DA. There is one basin that 1

6 makes up the berm of the detention pond that will drain the outside slope of embankment and cannot be captured in the pond. This basin will be known as OS1. The maximum allowable release rate for Detention Pond A is 2.00 cfs. This release rate is the peak 5-year historic flow calculated using the CUHP and a runoff coefficient based on a 2% impervious land percentage. An emergency overflow spillway has also been sized to pass the 100-year developed runoff in the event that the outlet structure becomes clogged. II. Drainage Basins and Sub-basins A. Major Basin Description A.1 On-Site Flows The developed basins were defined for the site and identified as Basins DA, DB and DC. Basin DA is 8.80 acres, DB is 0.61 acres and DC is 0.28 acres. For specific details on the design of the detention pond, see Section V, Drainage Facility Design in this report. For more details on the location of the major basins, see the Drainage Exhibit in Appendix C. A.2 Off-Site Flows There are no off-site basins that have been routed through the site. B. Sub-basin Description The developed basin DA has been broken down into four sub-basins for the purpose of analyzing runoff flows at particular design points, while DB and DC have not been subdivided. III. Drainage Design Criteria A. Regulations The primary criterion for the storm water management for this project is Weld County Engineering and Construction Criteria as published by Weld County, April The supplemental criterion is Urban Storm Drainage Criteria Manual, (USDCM) Volumes I, II, & III, as published by the Urban Drainage and Flood Control District, Denver, Colorado. Charts, graphs, and tables used in design are included in the Appendices at the back of this report. 2

7 B. Development Criteria Reference and Constraints The main criterion with this project is to provide the necessary detention for the proposed development of the Red Barn R.V. and Boat Storage facility, and to safely route the excess runoff to the detention pond. An emergency overflow spillway weir will be provided on the north side of the detention pond for the 100-year developed peak runoff that will discharge along the historic path to the east if the pond outlet becomes clogged. Detention Pond A will be designed with a staged outlet structure with orifice plates that will limit the release rate to allow for a 40-hour drain time from the Water Quality Capture Volume and limit release from larger storm events to a 5-year historic level. C. Hydrological Criteria Table 3-1, Incremental Rainfall Depth/Return Period for City of Greeley was used as input for the Colorado Urban Hydrograph Procedure (CUHP) rainfall depths. CUHP was used to analyze the developed storm for the developed basin DA to determine a detention pond capacity. Two intervals will be analyzed as part of this drainage design. The 10-year storm will be analyzed as the initial storm, and 100-year storm will be analyzed as the major storm for the entire site. The Natural Resources Conservation Service, (Web Soil Survey Site) from the United States Department of Agriculture was used to determine the hydrologic soil type for the site. The site consists of NRCS soil groups A & C. Composite runoff coefficient C values from the USDCM for each soil type will be used when calculating the storm events for the site. D. Hydraulic Criteria Manning s Equation will be used to size the open channels for this project. The hydraulic capacity of the detention pond outlet was designed based on the 5-year historic release rate calculation, and open channel techniques will be used to route the spillway flow according to the Weld County Engineering and Construction Criteria. E. Waiver/Variance from Criteria There are no variances requested for the Red Barn R.V. and Boat Storage facility project. F. Stormwater Quality Considerations An Erosion Control Plan will be incorporated into the construction plans during final design. Vehicle tracking control, silt fence, grading techniques and other erosion control and stormwater quality best management practices will be used to reduce sediment that might otherwise leave the project site during construction. The proposed detention pond will 3

8 include a Water Quality Capture Volume to allow additional sediment to settle out of the water before being discharged along the historic flow path. IV. Wetland Preservation & Mitigation There are no wetland areas that will be disturbed with the proposed improvements for Red Barn R.V. and Boat Storage. V. Drainage Facility Design A. General Concept The site will convey all on-site drainage safely via surface flow and trickle channels to the detention pond. The pond outlet and spillway will be located so that all released flows can continue safely along the historic travel path. Detention Pond A was sized using the CUHP method. See Appendix A for more details. The tables, charts, and figures used in the drainage design are included in the appendices at the back of this report. B. Specific Details The total on-site tributary area to Detention Pond A is 8.80 acres. The composite 100-year developed imperviousness was estimated to be percent from combining the three basins. The Detention Pond A water quality outlet structure shall be designed with orifice plates that limit the overall pond release rates to a 5-year historic level for the 10-year and 100-year developed events. The pond spillway elevation will be designed for the 100-year developed peak flow for the combined basins if the outlet structure should become clogged. Summaries of proposed Detention Pond A, are provided in the table below. See Appendix A, Detention Pond Sizing for more information. Table 1 Detention Pond A Summary Area Tributary to Detention Pond 8.80 Acres Detention Pond Storage Required (Design) 1.40 Ac-Ft WQCV Volume Required 0.16 Ac-Ft Total Volume Required 1.56 Ac-Ft Maximum Release Rate 2.0 cfs Pond Bottom Elevation Year Water Surface Elevation Spillway High Water Elevation Freeboard 1.07 Ft Top of Berm Elevation

9 VI. Conclusions A. Compliance with Standards The drainage design for this project complies with the intent of the Weld County Engineering and Construction Criteria. The design also complies with the provisions of the USDCM. B. Drainage Concept We believe that the drainage facility design will be effective in controlling impacts to property from stormwater runoff, and will ensure a reasonable level of safety and well-being for residents of the area. VII. References Weld County Engineering and Construction Criteria, Weld County, Colorado, April Design Criteria and Construction Specifications, Volume II and III Storm Drainage Design Criteria, City of Greeley Public Works Department, March 2007, Addendum June Urban Storm Drainage Criteria Manual, Volumes I, II, & III, Urban Drainage and Flood Control District, Denver, Colorado. The Natural Resources Conservation Service, (Web Soil Survey Site) from the United Department of Agriculture. 5

10 APPENDI A CALCULATIONS I. BASIN CHARACTERISTICS 7 VICINITY MAP 8 SOIL MAP 9 SOIL & WATER FEATURES FEMA FLOOD MAP 14 COMPOSITE % IMP., C VALUES, & HORTON S PARAMETERS WEIGHTED SLOPE TIME OF CONCENTRATION 24 HISTORIC & DEVELOPED BASINS MAP II. DETENTION POND SIZING 27 ETENDED DETENTION BASIN WQCV 28 ORIFICE PLATE DESIGN 29 CUHP SUBCATCHMENTS 30 CUHP INCREMENTAL RAINFALL DEPTHS 31 CUHP OUTPUT HYDROGRAPHS 32 CUHP CALCULATED OUTPUT PARAMETERS 33 DEVELOPED BASIN VOLUME CALCULATIONS DETENTION POND CAPACITY SPILWAY DESIGN 39 III. FLOW ROUTING AND DESIGN CALCULATIONS 40 5-Yr & 100-Yr. HISTORIC ROUTING Yr & 100-Yr. DEVELOPED ROUTING APPENDI B 45 GRAPHS, CHARTS APPENDI C DRAWING IN POCKET - 60 DRAINAGE EHIBIT 6

11 I. Basin Characteristics 7

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13 104 56' 29'' W ' 39'' W Hydrologic Soil Group Larimer County Area, Colorado; and Weld County, Colorado, Southern Part ( Moore Storage Facility) ' 34'' N ' 34'' N Warning: Soil Map may not be valid at this scale ' 24'' N 40 33' 24'' N Map Scale: 1:1,550 if printed on A portrait (8.5" x 11") sheet. N Meters 120 Feet Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey ' 29'' W ' 39'' W /29/2016 Page 1 of 5

14 MAP LEGEND MAP INFORMATION 11/29/2016 Page 2 of 5 Hydrologic Soil Group Larimer County Area, Colorado; and Weld County, Colorado, Southern Part ( Moore Storage Facility) Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 11, Sep 23, 2016 Soil Survey Area: Weld County, Colorado, Southern Part Survey Area Data: Version 15, Sep 22, 2016 Your area of interest (AOI) includes more than one soil survey area. These survey areas may have been mapped at different scales, with a different land use in mind, at different times, or at different levels of detail. This may result in map unit symbols, soil properties, and interpretations that do not completely agree across soil survey area boundaries. Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Apr 22, 2011 Apr 28, 2011 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background 10 Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey

15 MAP LEGEND MAP INFORMATION imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. 11/29/2016 Page 3 of 5 Hydrologic Soil Group Larimer County Area, Colorado; and Weld County, Colorado, Southern Part ( Moore Storage Facility) 11 Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey

16 Hydrologic Soil Group Larimer County Area, Colorado; and Weld County, Colorado, Southern Part Moore Storage Facility Hydrologic Soil Group Hydrologic Soil Group Summary by Map Unit Larimer County Area, Colorado (CO644) Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 53 Kim loam, 1 to 3 percent slopes 107 Thedalund loam, 0 to 3 percent slopes B % C % Subtotals for Soil Survey Area % Totals for Area of Interest % Hydrologic Soil Group Summary by Map Unit Weld County, Colorado, Southern Part (CO618) Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 32 Kim loam, 1 to 3 percent slopes 64 Thedalund loam, 1 to 3 percent slopes A % C % Subtotals for Soil Survey Area % Totals for Area of Interest % Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/29/2016 Page 4 of 5 12

17 Hydrologic Soil Group Larimer County Area, Colorado; and Weld County, Colorado, Southern Part Moore Storage Facility Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/29/2016 Page 5 of 5 13

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19 COMPOSITE RUNOFF VALUES Project Name : Red Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : Composite "C" Values & % Impervious - Basins Check By : MCK Percent Impervious SOIL GROUP "A" SOIL GROUP "C & D" AREA TOTAL AREA OF % AREA OF % AREA OF % AREA OF % AREA OF % AREA OF % AREA OF % AREA OF % AREA OF % AREA OF % COMPOSITE DESIGNATION AREA Gravel IMP. Roof IMP. Paved IMP. Lawn/Open IMP. Recycled IMP. Gravel IMP. Roof IMP. Paved IMP. Lawn/Open IMP. Recycled IMP. % IMP. Acre Asphalt Asphalt HISTORIC BASIN HA HB HC Σ DEVELOPED BASIN DB DC Σ DEVELOPED SUB-BASINS DA DA DA Σ OFFSITE DEVELOPED BASIN OS

20 COMPOSITE RUNOFF VALUES Project Name : Red Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : Composite "C" Values & % Impervious - Basins Check By : MCK Composite 5-yr Storm C A=0.93i CB=0.93i CC/D=0.87i AREA TOTAL COMPOSITE SOIL GROUP A SOIL GROUP B SOIL GROUP C DESIGNATION AREA % IMP. AREA RUNOFF AREA RUNOFF AREA RUNOFF COMPOSITE Acre ( i ) COEFF. COEFF. COEFF. "C" HISTORIC BASIN HA HB HC Σ DEVELOPED BASIN DB DC Σ DEVELOPED SUB-BASINS DA DA DA Σ OFFSITE DEVELOPED BASIN OS

21 COMPOSITE RUNOFF VALUES Project Name : Red Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : Composite "C" Values & % Impervious - Basins Check By : MCK Composite 10-yr Storm C A=0.94i CB=0.81i CC/D=0.74i+0.2 AREA TOTAL COMPOSITE SOIL GROUP A SOIL GROUP B SOIL GROUP C DESIGNATION AREA % IMP. AREA RUNOFF AREA RUNOFF AREA RUNOFF COMPOSITE Acre ( i ) COEFF. COEFF. COEFF. "C" HISTORIC BASIN HA HB HC Σ DEVELOPED BASIN DB DC Σ DEVELOPED SUB-BASINS DA DA DA Σ OFFSITE DEVELOPED BASIN OS

22 COMPOSITE RUNOFF VALUES Project Name : Red Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : Composite "C" Values & % Impervious - Basins Check By : MCK Composite 100-yr Storm C A=0.81i CB=0.49i CC/D=0.45i AREA TOTAL COMPOSITE SOIL GROUP A SOIL GROUP B SOIL GROUP C DESIGNATION AREA % IMP. AREA RUNOFF AREA RUNOFF AREA RUNOFF COMPOSITE Acre ( i ) COEFF. COEFF. COEFF. "C" HISTORIC BASIN HA HB HC Σ DEVELOPED BASIN DB DC Σ DEVELOPED SUB-BASINS DA DA DA Σ OFFSITE DEVELOPED BASIN OS Horton's Initial Infiltration 18

23 COMPOSITE RUNOFF VALUES Project Name : Red Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : Composite "C" Values & % Impervious - Basins Check By : MCK Horton's Decay Coefficient AREA TOTAL COMPOSITE SOIL GROUP A SOIL GROUP B SOIL GROUP C DESIGNATION AREA % IMP. AREA Decay AREA Decay AREA Decay COMPOSITE Acre ( i ) Coeff. Coeff. Coeff. COEFF. HISTORIC BASIN HA HB HC Σ DEVELOPED BASIN DB DC Σ VELOPED SUB-BASINS DA DA DA Σ OFFSITE DEVELOPED BASIN OS

24 COMPOSITE RUNOFF VALUES Project Name : Red Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : Composite "C" Values & % Impervious - Basins Check By : MCK Horton's Initial Infiltration AREA TOTAL COMPOSITE SOIL GROUP A SOIL GROUP B SOIL GROUP C DESIGNATION AREA % IMP. AREA Initial AREA Initial AREA Initial COMPOSITE Acre ( i ) Infiltration Infiltration Infiltration COEFF. HISTORIC BASIN HA HB HC Σ DEVELOPED BASIN DB DC Σ DEVELOPED SUB-BASINS DA DA DA Σ OFFSITE DEVELOPED BASIN OS

25 COMPOSITE RUNOFF VALUES Project Name : Red Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : Composite "C" Values & % Impervious - Basins Check By : MCK Horton's Final Infiltration AREA TOTAL COMPOSITE SOIL GROUP A SOIL GROUP B SOIL GROUP C DESIGNATION AREA % IMP. AREA Final AREA Final AREA Final COMPOSITE Acre ( i ) Infiltration Infiltration Infiltration COEFF. HISTORIC BASIN HA HB HC Σ DEVELOPED BASIN DB DC Σ DEVELOPED SUB-BASINS DA DA DA Σ OFFSITE DEVELOPED BASIN OS

26 HISTORIC BASIN WEIGHTED SLOPE Project Name : Red Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : Major Basin Weighted Slope Check By : MCK SLOPE i = [ L 1 S L 2 S L n S n 0.24 / (L 1 + L L n )] 4.17 = AVERAGE BASIN SLOPE L 1, L 2, L n = Length of Corresponding Reaches in ft. S 1, S 2, S n = Slope of Individual Reaches in ft/ft. HISTORIC BASIN HA Initial Time, Ti Ln Sn % Sn ( ft/ft) Ln Sn Sn 0.24 Ln Sn % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % Σ ft. Σ S = % 22

27 DEVELOPED BASIN WEIGHTED SLOPE Project Name : Red Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : Major Basin Weighted Slope Check By : MCK SLOPE i = [ L 1 S L 2 S L n S n 0.24 / (L 1 + L L n )] 4.17 = AVERAGE BASIN SLOPE L 1, L 2, L n = Length of Corresponding Reaches in ft. S 1, S 2, S n = Slope of Individual Reaches in ft/ft. DEVELOPED BASIN DA Initial Time, Ti Ln Sn % Sn ( ft/ft) Ln Sn Sn 0.24 Ln Sn % % % % % % % % Σ ft. Σ S = % Travel Time, Tt Ln Sn % Sn ( ft/ft) Ln Sn Sn 0.24 Ln Sn % % % % % % % % % % % % % % % % % Σ ft. Σ S = % Time of Concentration, Tc Ln Sn % Sn ( ft/ft) Ln Sn Sn 0.24 Ln Sn % % % % % % % % % % % % % % % % % % % % % % % % % Σ ft. Σ S = % 23

28 Ketterling Butherus & Norton Engineers, LLC. TIME OF CONCENTRATION Project Name : Red Barn RV and Boat Storage Project No. : Location : Weld County, CO Computation By : KLR Item : Time of Concentration (Initial & Travel Time) Check By : MCK COMP tc CHECK FINAL tc (URBANIZED BASINS) tc TRAVEL TIME (tt) INITIAL/OVERLAND TIME (ti) SUB-BASIN DATA TOTAL Min. of REMARKS tc= (18-15i)+(L/60(24i+1 2)SQRT(S) (11) & (13) DESIGN HYDROLOGIC AREA C5 LENGTH SLOPE ti LENGTH SLOPE VEL tt ti + tt LENGTH SOIL GROUP (Ac) (Ft) (%) (MIN) (Ft) (%) (FPS) (MIN) (MIN) (Ft) (MIN) (MIN) (1) (%) (2) (3) (4) (5) (6) (7) (C V ) (8) (9) (10) (11) (12) (13) (14) CONVE- YANCE COEFFICIEN T PERCENT IMPER- VIOUS HA A/C HB A/C use min. tc of 10 for non-urban HC A use min. tc of 10 for non-urban DA A/C DA1 A/C DA2 C DA3 C DB A/C use min. tc of 10 for non-urban DC A use min. tc of 10 for non-urban OS1 C use min. tc of 10 for non-urban 24

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31 II. Detention Pond Sizing 27

32 ETENDED DETENTION BASIN (EDB) - SEDIMENTATION FACILITY Project Name : Red Barn RV and Boat Storage Location : Weld County, CO Item : Extended Detention Basin (Basin "DA") 1. Basin Storage Volume A) Tributary Area's Imperviousness Ratio ( i = Ia/100 ) B) Contributing Watershed Area (Area) C) Water Quality Capture Volume (WQCV) Figure EDB-2, 40-hour Drain Time D) Design Volume: Vol = (WQCV/12) * Area Project Number : Computation By : KLR Check By : MCK Ia = i= Area = acres WQCV = watershed inches % Vol = acre-feet 7, cu-ft Orifice Plate Perforated Riser Pipe Other: 2. Outlet Works A) Outlet Type (Check One) B) Depth at Outlet Above Lowest Perforation (H) H= 1.06 feet C) Required Maximum Outlet Area per Row (Ao) Figure EDB-3 D) Perforation Dimensions (enter one only): I) Circular Perforation Diameter OR ii) 2" Height Rectangular Perforation Width (Ao) = 0.74 square inches D= W= 11/16 inches OR inches nc 2 (Ao) = 0.74 nr 1 (Aot) = 0.74 square inches 3/8 inches E) Number of Columns (nc, See Table 6a-1 for Max.) F) Actual Design Outlet Area per Row (Ao) G) Number of Rows 4" apart (nr) H) Total Outlet Area (Aot) I) Minimum Plate Thickness J) Discharge From Perforations number square inches number Hole Dia Hole Dia Area per Row (sq in) (in) * (in) n=1 n=2 n=3 1/ / / / / / / / / / / / / / / / / / / / / / / / / / / n - Number of columns of perforations Minimum steel 1/4" 5/16" 3/8" Q Figure 3-2. WQCV based on BMP Drain Time Figure EDB-3 28

33 ORIFICE PLATE DESIGN Project Name : Red Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : Pond Outlet Restrictor Plate Check By : MCK 2.00 CFS (5-yr Historic, Release Rate) 2.00 CFS Qrelease Total Input Variables Elevation D=Proposed Pipe Diameter, In 1 4, High Water Elevation 2.00 Q=Maximum allowable discharge. cf/s 4, Pipe Invert Elevation 0.65 C=coefficient of discharge 2.34 Head (h) g=acceleration due to gravity, ft/second squared 2.34 h=head on horizontal center line of orifice, ft Area OK 0.25 Area of Opening, sf 0.79 = Total Pipe Area, sf OK Area of Opening, sq. in Dimension "b", in Actual Area, sq. in Q=Maximum Discharge A = C Q ( 2gh ) ORIFICE PLATE DISCHARGE PIPE b x Conditions : D = IN 1 FT q/qf = 0.90 FIGURE 6-1 Q = 2.00 CFS d/df = d = 0.74 FT S = 0.51% v/vf = v = 3.18 FPS n = E.G = 0.42% Calculation (Full): A = 0.79 S.F. V = 2.82 FPS Q = 2.21 CFS 29

34 CUHP SUBCATCHMENTS Columns with this color heading are for required user-input Columns with this color heading are for optional override values Columns with this color heading are for program-calculated values Subcatchment Name A Raingage Area (acre) Length to Centroid (ft) Length (ft) Slope (ft/ft) Maximum Depression Storage (Watershed inches) Percent Imperviousness Pervious Impervious Initial Rate (in/hr) Horton's Infiltration Parameters Decay Coefficient (1/seconds) HA Greeley 5-yr DA 5-yr Greeley 5-yr DA 10-yr Greeley 10-yr DA 100-yr Greeley 100-yr Final Rate (in/hr) 30

35 Comment DESIGN STORM FOR GREELEY (INCREMENTAL RAINFALL DEPTH/RETURN PERIOD) Note: Time must be of the form h:mm. Entering an improperly formatted time value (eg: 0:120 instead of 2:00) may reset the number format. The number format can be reapplied in the "Format Cells" Dialog Window. Time 5-yr Depth 10-yr Depth 100-yr Depth 0: : : : : : : : : : : : : : : : : : : : : : : : :

36 Printouts for Storm Hydrographs flow in cfs time in minutes HA 5 yr DA 5 yr DA 10 yr DA 100 yr

37 Summary of Unit Hydrograph Parameters Used By Program and Calculated Results (Version 1.4.0) Catchment Name/ID Ct Cp W50 (min.) Unit Hydrograph Parameters and Results Excess Precip. Storm Hydrograph W50 Before Peak W75 (min.) W75 Before Peak Time to Peak (min.) Peak (cfs) Volume (c.f) Excess (inches) Excess (c.f.) Time to Peak (min.) Peak Flow (cfs) HA , , , DA 5 yr , , , DA 10 yr , , , DA 100 yr , , , Total Volume (c.f.) Runoff per Unit Area (cfs/acre) 33

38 DEVELOPED BASIN POND VOLUME Project NamRed Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : DETENTION POND SIZING - 10 YEAR Check By : MCK TIME DELAY (MIN) TIME INCREMENT (MIN) OUTPUT DISCHARGE (CFS) TOTAL VOLUME (ACRE-FT) WQCV (ACRE-FT) VOLUME (ACRE-FT) VOLUME (CU. FT.) AREA (RAW) AREA PASSED 20.0 STORM HYDROGRAPH (CFS) TIME (MIN) >>> INFLOW OUTFLOW ECEEDED STORM HYDROGRAPH (CFS) TIME 0 (MIN)

39 DEVELOPED BASIN POND VOLUME Project NamRed Barn RV and Boat Storage Project Name : Location : Weld County, CO Computation By : KLR Item : DETENTION POND SIZING YEAR Check By : MCK TIME DELAY (MIN) TIME INCREMENT (MIN) OUTPUT DISCHARGE (CFS) TOTAL VOLUME (ACRE-FT) WQCV (ACRE-FT) VOLUME (ACRE-FT) VOLUME (CU. FT.) AREA (RAW) AREA PASSED 40.0 STORM HYDROGRAPH (CFS) TIME (MIN) >>> INFLOW OUTFLOW ECEEDED STORM HYDROGRAPH (CFS) E E E E TIME (MIN)

40 DETENTION POND WQCV CAPACITY Project Name : Red Barn RV and Boat Storage Project Number: Location : Weld County, CO Calculated By : KLR Item : Detention Pond Capacity Calculation For Basin DA Checked By: MCK ACTUAL STORAGE : (A) (B) (C) (D) Elevation Depth Area Volume Σ Volume Σ Volume (Sf.) (Cf.) (Cf.) (Ac.-ft.) 4, Total Volume = 7, ft Elev. (A1) = 4, , , Σ Volume (D1) = 3, Volume Req'd , , Partial volume (C2) = 9, >>>>>>>>> 4, , Depth, partial volume = , , , , WQCV water level = , , Free board = , , Top pond bank elevation = , , , , , , , , , , , , Required WQCV = 0.17 acre-feet 36

41 10-YR DETENTION POND CAPACITY Project Name : Red Barn RV and Boat Storage Project Number: Location : Weld County, CO Calculated By : KLR Item : Detention Pond Capacity Calculation For Basin DA Checked By: MCK ACTUAL STORAGE : (A) (B) (C) (D) Elevation Depth Area Volume Σ Volume Σ Volume (Sf.) (Cf.) (Cf.) (Ac.-ft.) 4, Total Volume = 33, ft Elev. (A1) = 4, , , Σ Volume (D1) = 15, , , Partial volume (C2) = 17, , , Depth, partial volume = 0.50 Volume Req'd , , >>>>>>>>> 4, , yr water level = , , Free board = , , Top pond bank elevation = , , , , , , , , , , , , Required 10-yr Volume for Extended Detntion Basin = 0.76 acre-feet 37

42 ULTIMATE DETENTION POND CAPACITY Project Name : Red Barn RV and Boat Storage Project Number: Location : Weld County, CO Calculated By : KLR Item : Detention Pond Capacity Calculation For Basin DA Checked By: MCK ACTUAL STORAGE : (A) (B) (C) (D) Elevation Depth Area Volume Σ Volume Σ Volume (Sf.) (Cf.) (Cf.) (Ac.-ft.) 4, Total Volume = 67, ft Elev. (A1) = 4, , , Σ Volume (D1) = 58, , , Partial volume (C2) = 36, , , Depth, partial volume = , , , , High water level = , , Free board = , , Top pond bank elevation = Volume Req'd , , >>>>>>>>> 4, , , , , , , , , , Required Volume for Extended Detntion Basin = 1.56 acre-feet 38

43 SPILLWAY DESIGN CALCULATION Project Name : Red Barn RV and Boat Storage Project Number : Location : Weld County, CO Computation By : KLR Item : Detention Pond Spillway Check By : MCK Size Overflow For 100-yr Plugged Condtions MA. RELEASE FROM SPILLWAY = (Cfs) Assuming the outlet pipe is plugged at the start of the storm, by the time the water level reaches the overflow, the flow into the pond will be Weir Flow : General form of the equation : Q = CL(H) 3/2 D = Discharge (CFS) C = 2.62 C = Weir Coefficient (2.62) H = 0.29 L = Horizontal Length (feet) L = H = Total Energy Head (feet) Q = > ok. 39

44 III. Flow Routing and Design Calculations 40

45 STORM DRAINAGE SYSTEM DESIGN DATA Project Name : Red Barn RV and Boat Storage Project Number : Location : Weld County, CO Computation By : KLR Item : Initial Storm 5 Yr. Event Check By : MCK Flow Time Location of Design Point Basin Length (ft.) Initial Time (min.) (ti) Street (min.) (tt) Pipe (min.) Time of Concentration (min.) Coefficent -C- Intensity -Iin/hr Area -A- (ac.) Direct Runoff (cfs) Remarks H1 HA H2 HB min. tc for non-urban areas H3 HC min. tc for non-urban areas 41

46 STORM DRAINAGE SYSTEM DESIGN DATA Project Name : Red Barn RV and Boat Storage Project Number : Location : Weld County, CO Computation By : KLR Item : Major Storm 100 Yr. Event Check By : MCK Flow Time Location of Design Point Basin Length (ft.) Initial Time (min.) (ti) Street (min.) (tt) Pipe (min.) Time of Concentration (min.) Coefficent -C- Intensity -Iin/hr Area -A- (ac.) Direct Runoff (cfs) Remarks H1 HA H2 HB min. tc for non-urban areas H3 HC min. tc for non-urban areas 42

47 STORM DRAINAGE SYSTEM DESIGN DATA Project Name : Red Barn RV and Boat Storage Location : Weld County, CO KLR Item : Initial Storm 5 Yr. Event MCK Flow Time Location of Design Point Basin Length (ft.) Initial Time (min.) (ti) Street (min.) (tt) Pipe (min.) Time of Concentra- tion (min.) Coefficent -C- Intensity -Iin/hr Area -A- (ac.) Direct Runoff (cfs) Direct Runoff Remarks 1 DA DA DA DP DP OS DB DC

48 STORM DRAINAGE SYSTEM DESIGN DATA Project Name : Red Barn RV and Boat Storage Location : Weld County, CO KLR Item : Major Storm 100 Yr. Event MCK Flow Time Location of Design Point Basin Length (ft.) Initial Time (min.) (ti) Street (min.) (tt) Pipe (min.) Time of Concentra- tion (min.) Coefficent -C- Intensity -Iin/hr Area -A- (ac.) Direct Runoff (cfs) Direct Runoff Remarks 1 DA DA DA DP DP OS DB DC

49 Appendix B - Graph, Charts A) Recommended Time of Concentration Equation. B) Recommended Percentage Imperviousness Values. C) Recommended Runoff Coefficient, C. D) NOAA Point Precipitation Data. E) Extended Duration-Intensity-Frequency Tabulation. F) Typical Depression Losses for Various Land Covers and Recommended Horton s Equation Parameters. 45

50 Runoff Chapter Limitations The Rational Method is the simplistic approach for estimating the peak flow rate and total runoff volume from a design rainstorm in a given catchment. Under the assumption of uniform hydrologic losses, the method is limited to catchments smaller than 90 acres. Under the condition of composite soils and land uses, the area-weighted method is recommended to derive the catchment s hydrologic parameters. The greatest drawback to the Rational Method is that it normally provides only one point (the peak flow rate) on the runoff hydrograph. When the areas become complex and where subcatchments come together, the Rational Method will tend to overestimate the actual flow, which results in oversizing of drainage facilities. The Rational Method provides no means or methodology to generate and route hydrographs through drainage facilities. One reason the Rational Method is limited to small areas is that good design practice requires the routing of hydrographs for larger catchments to achieve an economically sound design. Another disadvantage of the Rational Method is that with typical design procedures, one normally assumes that all of the design flow is collected at the design point and that there is no water running overland to the next design point. This is not a fault of the Rational Method but of the design procedure. The Rational Method must be modified, or another type of analysis must be used, when analyzing an existing system that is under-designed or when analyzing the effects of a major storm on a system designed for the minor storm. 2.4 Time of Concentration One of the basic assumptions underlying the Rational Method is that runoff is linearly proportional to the average rainfall intensity during the time required for water to flow from the most remote part of the drainage area to the design point. In practice, the time of concentration is empirically estimated along the selected waterway through the catchment. The waterway is first divided into overland flow length and channelized flow lengths, according to the channel characteristics. For urban areas, the time of concentration, t c, consists of an initial time or overland flow time, t i, plus the channelized flow travel time, t t, through the storm drain, paved gutter, roadside ditch, or channel. For non-urban areas, the time of concentration consists of an overland flow time, t i, plus the time of travel in a defined drainage path, such as a swale, channel, or stream. The channelized flow travel time portion, t t, of the time of concentration can be estimated from the hydraulic properties of the conveyance element. Initial or overland flow time, on the other hand, will vary with surface slope, depression storage, surface cover, antecedent rainfall, and infiltration capacity of the soil, as well as distance of surface flow. The time of concentration is computed by Equation 6-2 for both urban and non-urban areas: t c ti tt Equation 6-2 Where: t c = computed time of concentration (minutes) t i = overland (initial) flow time (minutes) t t = channelized flow time (minutes). 6-4 Urban Drainage and Flood Control District January 2016 Urban Storm Drainage Criteria Manual Volume 1 46

51 Chapter 6 Runoff Initial or Overland Flow Time The initial or overland flow time, t i, may be calculated using Equation 6-3: t i C L 5 Equation So Where: t i = overland (initial) flow time (minutes) C 5 = runoff coefficient for 5-year frequency (from Table 6-4) L = length of overland flow (ft) S o = average slope along the overland flow path (ft/ft). Equation 6-3 is adequate for distances up to 300 feet in urban areas and 500 feet in rural areas. Note that in a highly urbanized catchment, the overland flow length is typically shorter than 300 feet due to effective man-made drainage systems that collect and convey runoff Channelized Flow Time The channelized flow time (travel time) is calculated using the hydraulic properties of the conveyance element. The channelized flow time, t t, is estimated by dividing the length of conveyance by the velocity. The following equation, Equation 6-4 (Guo 2013), can be used to determine the flow velocity in conjunction with Table 6-2 for the conveyance factor. t t L t t Equation K S o L 60V t Where: t t = channelized flow time (travel time, min) L t = waterway length (ft) S o = waterway slope (ft/ft) V t o K = NRCS conveyance factor (see Table 6-2). Table 6-2. NRCS Conveyance factors, K Type of Land Surface Conveyance Factor, K Heavy meadow 2.5 Tillage/field 5 Short pasture and lawns 7 Nearly bare ground 10 Grassed waterway 15 Paved areas and shallow paved swales 20 January 2016 Urban Drainage and Flood Control District 6-5 Urban Storm Drainage Criteria Manual Volume 1 47

52 Runoff Chapter 6 The time of concentration, t c, is the sum of the initial (overland) flow time, t i, and the channelized flow time, t t, as per Equation First Design Point Time of Concentration in Urban Catchments Equation 6-4 was solely determined by the waterway characteristics and using a set of empirical formulas. A calibration study between the Rational Method and the Colorado Urban Hydrograph Procedure (CUHP) suggests that the time of concentration shall be the lesser of the values calculated by Equation 6-2 and Equation 6-5 (Guo and Urbonas 2013). tc i L t (18 15 ) Equation (24i 12) So Where: t c = minimum time of concentration for first design point when less than t c from Equation 6-1. L t = length of flow path (ft) i = imperviousness (expressed as a decimal) S o = slope of flow path (ft/ft). Equation 6-5 is the regional time of concentration that warrants the best agreement on peak flow predictions between the Rational Method and CUHP. It was developed using the UDFCD database that includes 295 sample urban catchments under 2-, 5-, 10-, 50, and 100-yr storm events (MacKenzie 2010). It suggests that both initial flow time and channelized flow velocity are directly related to the catchment s imperviousness (Guo and MacKenzie 2013). The first design point is defined as a node where surface runoff enters the storm drain system. For example, all inlets are first design points because inlets are designed to accept flow into the storm drain. Typically, but not always, Equation 6-5 will result in a lesser time of concentration at the first design point and will govern in an urbanized watershed. For subsequent design points, add the travel time for each relevant segment downstream Minimum Time of Concentration Use a minimum t c value of 5 minutes for urbanized areas and a minimum t c value of 10 minutes for areas that are not considered urban. Use minimum values even when calculations result in a lesser time of concentration Common Errors in Calculating Time of Concentration A common mistake in urbanized areas is to assume travel velocities that are too slow. Another common error is to not check the runoff peak resulting from only part of the catchment. Sometimes a lower portion of the catchment or a highly impervious area produces a larger peak than that computed for the whole catchment. This error is most often encountered when the catchment is long or the upper portion contains grassy open land and the lower portion is more developed. 6-6 Urban Drainage and Flood Control District January 2016 Urban Storm Drainage Criteria Manual Volume 1 48

53 Chapter 6 Runoff 2.5 Rainfall Intensity The calculated rainfall intensity, I, is the average rainfall rate in inches per hour for the period of maximum rainfall having a duration equal to the time of concentration. After the design storm recurrence frequency has been selected, a graph should be made showing rainfall intensity versus time. The procedure for obtaining the local data and plotting such a graph is explained and illustrated in the Rainfall chapter of the USDCM. The UD-Rain Excel workbook can also be used for calculating the intensity. This workbook is available for download at Runoff Coefficient Photograph 6-2. Urbanization (impervious area) increases runoff volumes, peak discharges, frequency of runoff, and receiving stream degradation. Each part of a watershed can be considered as either pervious or impervious. The pervious part is the area where water can readily infiltrate into the ground. The impervious part is the area that does not readily allow water to infiltrate into the ground, such as areas that are paved or covered with buildings and sidewalks or compacted unvegetated soils. In urban hydrology, the percentage of pervious and impervious land is important. Urbanization increases impervious area causing rainfall-runoff relationships to change significantly. In the absence of stormwater management methods such as low impact development and green infrastructure, the total runoff volume increases, the time to the runoff peak rate decreases, and the peak runoff rate increases. When analyzing a watershed for planning or design purposes, the probable future percent of impervious area must be estimated. A complete tabulation of recommended values of the total percent of imperviousness is provided in Table 6-3. The runoff coefficient, C, represents the integrated effects of infiltration, evaporation, retention, and interception, all of which affect the volume of runoff. The determination of C requires judgment based on experience and understanding on the part of the engineer. Volume-based runoff coefficients were derived to establish the optimal consistency between CUHP and the Rational Method for peak flow predictions (Guo, 2013). Using the percentage imperviousness, the equations in Table 6-4 can be used to calculate the runoff coefficients for hydrologic soil groups A, B, and C/D for various storm return periods. January 2016 Urban Drainage and Flood Control District 6-7 Urban Storm Drainage Criteria Manual Volume 1 49

54 50

55 Chapter 6 Runoff Table 6-4. Runoff coefficient equations based on NRCS soil group and storm return period NRCS Soil Group Storm Return Period 2-Year 5-Year 10-Year 25-Year 50-Year 100-Year A C A = 0.89i C A = 0.93i C A = 0.94i C A = 0.944i C A = 0.95i C A = 0.81i B C B = 0.89i C B = 0.93i C B = 0.81i C/D C C/D = 0.89i C C/D = 0.87i Where: C C/D = 0.74i i = % imperviousness (expressed as a decimal) C B = 0.70i C C/D = 0.64i C B = 0.59i C C/D = 0.54i C A = Runoff coefficient for Natural Resources Conservation Service (NRCS) HSG A soils C B = Runoff coefficient for NRCS HSG B soils C C/D = Runoff coefficient for NRCS HSG C and D soils. C B = 0.49i C C/D = 0.45i The values for various catchment imperviousness and storm return periods are presented graphically in Figures 6-1 through 6-3, and are tabulated in Table 6-5. These coefficients were developed for the Denver region to work in conjunction with the time of concentration recommendations in Section 2.4. Use of these coefficients and this procedure outside of the semi-arid climate found in the Denver region may not be valid. The UD-Rational Excel workbook performs all the needed calculations to find the runoff coefficient given the soil type and imperviousness and the reader may want to take advantage of this macro-enabled Excel workbook that is available for download from the UDFCD s website See Examples 7.1 and 7.2 that illustrate the Rational Method. January 2016 Urban Drainage and Flood Control District 6-9 Urban Storm Drainage Criteria Manual Volume 1 51

56 1/20/2017 Precipitation Frequency Data Server NOAA Atlas 14, Volume 8, Version 2 Location name: Fort Collins, Colorado, USA* Latitude: , Longitude: Elevation: ft** * source: ESRI Maps ** source: USGS POINT PRECIPITATION FREQUENCY ESTIMATES Sanja Perica, Deborah Martin, Sandra Pavlovic, Ishani Roy, Michael St. Laurent, Carl Trypaluk, Dale Unruh, Michael Yekta, Geoffery Bonnin NOAA, National Weather Service, Silver Spring, Maryland PF_tabular PF_graphical Maps_&_aerials PF tabular PDS based point precipitation frequency estimates with 90% confidence intervals (in inches) 1 Duration 5 min 10 min 15 min 30 min 60 min 2 hr 3 hr 6 hr 12 hr 24 hr 2 day 3 day 4 day 7 day 10 day 20 day 30 day 45 day 60 day Average recurrence interval (years) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1.09 ( ) 1.29 ( ) 1.56 ( ) 1.79 ( ) 1.94 ( ) 2.07 ( ) 2.35 ( ) 2.60 ( ) 3.35 ( ) 3.95 ( ) 4.65 ( ) 5.21 ( ) ( ) ( ) ( ) ( ) ( ) 1.02 ( ) 1.11 ( ) 1.29 ( ) 1.54 ( ) 1.82 ( ) 2.11 ( ) 2.28 ( ) 2.41 ( ) 2.76 ( ) 3.07 ( ) 3.90 ( ) 4.55 ( ) 5.35 ( ) 6.00 ( ) ( ) ( ) ( ) ( ) 1.14 ( ) 1.35 ( ) 1.47 ( ) 1.71 ( ) 2.01 ( ) 2.31 ( ) 2.69 ( ) 2.87 ( ) 3.03 ( ) 3.47 ( ) 3.85 ( ) 4.78 ( ) 5.52 ( ) 6.46 ( ) 7.27 ( ) ( ) ( ) ( ) 1.15 ( ) 1.42 ( ) 1.69 ( ) 1.84 ( ) 2.14 ( ) 2.47 ( ) 2.79 ( ) 3.22 ( ) 3.42 ( ) 3.58 ( ) 4.09 ( ) 4.52 ( ) 5.52 ( ) 6.32 ( ) 7.36 ( ) 8.28 ( ) ( ) ( ) 1.15 ( ) 1.53 ( ) 1.90 ( ) 2.27 ( ) 2.48 ( ) 2.85 ( ) 3.20 ( ) 3.55 ( ) 4.02 ( ) 4.23 ( ) 4.42 ( ) 5.00 ( ) 5.47 ( ) 6.55 ( ) 7.41 ( ) 8.56 ( ) 9.62 ( ) ( ) 1.15 ( ) 1.40 ( ) 1.86 ( ) 2.34 ( ) 2.81 ( ) 3.07 ( ) 3.50 ( ) 3.85 ( ) 4.21 ( ) 4.70 ( ) 4.92 ( ) 5.11 ( ) 5.73 ( ) 6.23 ( ) 7.34 ( ) 8.24 ( ) 9.47 ( ) 10.6 ( ) ( ) 1.38 ( ) 1.69 ( ) 2.24 ( ) 2.83 ( ) 3.41 ( ) 3.75 ( ) 4.22 ( ) 4.57 ( ) 4.94 ( ) 5.42 ( ) 5.66 ( ) 5.86 ( ) 6.50 ( ) 7.00 ( ) 8.13 ( ) 9.06 ( ) 10.3 ( ) 11.5 ( ) 1.13 ( ) 1.65 ( ) 2.01 ( ) 2.67 ( ) 3.38 ( ) 4.10 ( ) 4.51 ( ) 5.05 ( ) 5.37 ( ) 5.75 ( ) 6.21 ( ) 6.45 ( ) 6.66 ( ) 7.30 ( ) 7.81 ( ) 8.94 ( ) 9.89 ( ) 11.2 ( ) 12.5 ( ) 1.39 ( ) 2.03 ( ) 2.48 ( ) 3.30 ( ) 4.21 ( ) 5.12 ( ) 5.65 ( ) 6.27 ( ) 6.55 ( ) 6.94 ( ) 7.33 ( ) 7.58 ( ) 7.80 ( ) 8.42 ( ) 8.90 ( ) 10.0 ( ) 11.0 ( ) 12.3 ( ) 13.6 ( ) 1.61 ( ) 2.36 ( ) 2.88 ( ) 3.83 ( ) 4.91 ( ) 5.98 ( ) 6.62 ( ) 7.29 ( ) 7.52 ( ) 7.92 ( ) 8.24 ( ) 8.50 ( ) 8.72 ( ) 9.31 ( ) 9.76 ( ) 10.8 ( ) 11.8 ( ) 13.1 ( ) 14.4 ( ) 1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS). Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values. Please refer to NOAA Atlas 14 document for more information. Back to Top PF graphical &data=depth&units=english&series=pds 1/4 52

57 1/20/2017 Precipitation Frequency Data Server Back to Top Maps & aerials Small scale terrain &data=depth&units=english&series=pds 2/4 53

58 1/20/2017 Precipitation Frequency Data Server 2km + 1mi Large scale terrain 100km + 60mi Large scale map 100km + 60mi Large scale aerial &data=depth&units=english&series=pds 3/4 54