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Home My WebLink About20230608 Ver 1_2023-04-06 - Chavis Street Soccer Fields - STORMWATER MANAGEMENT REPORT_20230426Stormwater Management Report Chavis Street Soccer Fields Low Density Project Franklinton, North Carolina April 6, 2023 Prepared By: The Nau Company, PLLC PO Box 810 Rolesville, North Carolina, 27571 (919) 625-3090 tnau@thenauco.com NCBELS License # P-0751 Stormwater Management Report April 6, 2023 Chavis Street Soccer Fields INTRODUCTION This report presents the stormwater management design for the proposed improvements at the Chavis Street Soccer Fields located on a parcel east of South Chavis Street and bounded by residential parcels (RSM zoning) in Franklinton, North Carolina. This project will fall under the NCDEQ requirements for Low Density Development. BACKGROUND The Chavis Street Soccer Field project is a proposed development that will consist of 6 soccer fields, parking lot and open space amenities. The total site area for the project is 17.52 acres (762,994 SF). The total disturbed area for the project is 15.7 acres. The total proposed impervious area for the project which consists of the driveway cut, parking lot and associated drive aisles is 1.83 acres (79,543 SF) or 10.43% of the total site area, which is well below the 24% threshold required for low density development status. Water services will be provided by Franklin County. Sewer service will be handled via septic fields. The proposed project will not be served by stormwater control measures (SCMs) as the project qualifies as a Low -Density Project under 15A NCAC 02H.1003 (2). However, the project has been designed to maximize dispersed flow through vegetated areas and to minimize channelization of flow. The project has also been designed to transport stormwater that cannot be released as dispersed flow via vegetated conveyances that will meet State requirements for stormwater flow. The purpose of this report is to present the calculations for the low -density development and the vegetated conveyances that will serve the Chavis Street Soccer Field project. REQUIREMENTS Stormwater Permits for the Town of Franklinton are issued by the North Carolina Division of Environmental Quality (NCDEQ). The relevant NCDEQ requirements for low density projects found in 15A NCAC 02H .1003 (1) and 15A NCAC 02H .1003 (2) are summarized below: CALCULATION OF PROJECT DENSITY. The following requirements shall apply to the calculation of project density: (a) Project density shall be calculated as the total built -upon area divided by the total project area; (b) A project with existing development may use the calculation method in Sub- Item (1)(a) or shall have the option of calculating project density as the difference of total built -upon area minus existing built -upon area divided by the difference of total project area minus existing built -upon area; (c) Total project area shall exclude the following: (i) areas below the Normal High Water Line (NHWL); and Stormwater Management Report April 6, 2023 Chavis Street Soccer Fields (ii) areas defined as "coastal wetlands" pursuant to 15A NCAC 07H .0205, herein incorporated by reference, including any subsequent amendments and editions, and may be accessed at no cost at http://reports.oah.state.nc.us/ncac.asp as measured landward from the Normal High Water (NHW) line; and (d) On a case -by -case basis as determined by the Division during application review, projects may be considered to have both high and low density areas based on one or more of the following criteria: (i) natural drainage area boundaries; (ii) variations in land use throughout the project; and (iii) construction phasing. • DENSITY THRESHOLDS. Low density projects shall not exceed the low -density development thresholds set forth in the stormwater programs to which they are subject pursuant to Rules .1017, .1019, and .1021 of this Section. For projects subject to the requirements for Non - Coastal High Quality Waters and Outstanding Resource Waters, dwelling unit per acre may be used instead of density to establish low density status for single-family detached residential development as set forth in Rule .1021 in this Section. • DISPERSED FLOW. Projects shall be designed to maximize dispersed flow through vegetated areas and minimize channelization of flow. VEGETATED CONVEYANCES. Stormwater that cannot be released as dispersed flow shall be transported by vegetated conveyances. A minimal amount of non -vegetated conveyances for erosion protection or piping for driveways or culverts under a road shall be allowed by the permitting authority when it cannot be avoided. Vegetated conveyances shall meet the following requirements: (i) Side slopes shall be no steeper than 3:1 (horizontal to vertical) unless it is demonstrated to the permitting authority that the soils and vegetation will remain stable in perpetuity based on engineering calculations and on -site soil investigation; and (ii) The conveyance shall be designed so that it does not erode during the peak flow from the 10-year storm as demonstrated by engineering calculations. • CURB OUTLET SYSTEMS. Low density projects may use curb and gutter with outlets to convey stormwater to grassed swales or vegetated areas. Requirements for these curb outlet systems [are] shall be as follows: (i) The curb outlets shall be designed such that the swale or vegetated area can carry the peak flow from the 10-year storm at a non -erosive velocity; (ii) The longitudinal slope of the swale or vegetated area shall not exceed five percent, except where not practical due to physical constraints. In these cases, devices to slow the rate of runoff and encourage infiltration to reduce pollutant delivery shall be provided; (iii) The swale's cross-section shall be trapezoidal with a minimum bottom width of two feet; (iv) The side slopes of the swale or vegetated area shall be no steeper than 3:1 (horizontal to vertical); (v) The minimum length of the swale or vegetated area shall be 100 feet; and Stormwater Management Report April 6, 2023 Chavis Street Soccer Fields (vi) Low density projects may use treatment swales designed pursuant to Rule .1061 of this Section in lieu of the requirements specified in Sub -Item (i) through (v) of this Rule. • VEGETATED SETBACKS. Vegetated setbacks shall be required adjacent to waters as specified in the stormwater rules to which the project is subject pursuant to this Section, in addition to the following requirements applicable to all vegetated setbacks: (a) The width of a vegetated setback shall be measured horizontally from the normal pool elevation of impounded structures, from the top of bank of each side of streams or rivers, and from the mean high waterline of tidal waters, perpendicular to the shoreline; (b) Vegetated setbacks may be cleared or graded, but shall be replanted and maintained in grass or other vegetation; (c) Built -upon area that meets the requirements of G.S. 143-214.7(b2)(2) shall be allowed within the vegetated setback. (d) Built -upon area that does not meet the requirements of G.S. 143-214.7(b2)(2) shall be allowed within a vegetated setback when it is not practical to locate the built -upon area elsewhere, the built -upon area within the vegetated setback is minimized, and channelizing runoff from the built -upon area is avoided. Builtupon area within the vegetated setback shall be limited to: (i) Publicly -funded linear projects such as roads, greenways, and sidewalks; (ii) Water Dependent Structures; and (iii) Minimal footprint uses such as poles, signs, utility appurtenances, and security lights. (e) Stormwater that has not been treated in an SCM shall not be discharged through a vegetated setback; instead it shall be released at the edge of the vegetated setback and allowed to flow through the setback as dispersed flow. (f) Artificial streambank and shoreline stabilization shall not be subject to the requirements of this Item. • STORMWATER OUTLETS. Stormwater outlets shall be designed so that they do not cause erosion downslope of the discharge point during the peak flow from the 10-year storm event as shown by engineering calculations. • DEED RESTRICTIONS AND PROTECTIVE COVENANTS. The permittee shall record deed restrictions and protective covenants prior to the issuance of a certificate of occupancy to ensure that projects will be maintained in perpetuity consistent with the plans and specifications approved by the permitting authority. For projects owned by public entities, the permittee shall have the option to incorporate specific restrictions and conditions into a facility management plan or another instrument in lieu of deed restrictions and protective covenants. • COMPLIANCE WITH OTHER REGULATORY PROGRAMS. Project designs shall comply with all other applicable requirements pursuant to G.S. 143-214.1, 143-214.5, 143-214.7, and 143- 215.3(a)(1). • PERMIT ISSUANCE. Stormwater management permits issued for low density projects shall not require permit renewal. Stormwater Management Report April 6, 2023 Chavis Street Soccer Fields PROPOSED STORMWATER CONVEYANCE MEASURE The design storm for this project is the 10-year 5-minute rainfall. A vegetated channel has been proposed to carry both on -site and offsite stormwater flows. Refer to the construction drawings for details of the channel. METHODOLOGY Drainage Areas and SCS Curve Numbers Drainage areas were delineated based on proposed and existing topography using CAD software. Land use types were measured using CAD software and SCS curve numbers were applied to each land use type within the drainage area to calculate a weighted, composite SCS Curve Number. Times of Concentration The minimum time of concentration used for calculation of peak flows was 5 minutes. For times of concentration more than 5 minutes, a simplified TR-55 method was used. The simplified method calculates the time of concentration only using sheet flow time and channel flow time — shallow concentrated flow time is disregarded. Since channel dimensions vary along the channel flow path, channel parameters were selected for the entire length of channel flow that yield a flow velocity of approximately 4.5 feet per second. A flow velocity of 4.5 feet per second is greater than or equal to actual flow velocities expected in the open channels along the flow path and therefore will yield a runoff higher that what would be expected at the analysis point. Runoff Runoff flowrates for the proposed channel were calculated using the Hydrology Studio software program. The software utilizes the SCS Methodology to determine peak flow rates and performs routing calculations to determine velocity and depth results for the channel. Rainfall Intensity The following rainfall intensity used in the calculations for this report were taken from the NOAA Precipitation Frequency Data Server (PFDS). A printout of this rainfall data is included as an appendix to this report. Rainfall event (Design Storm) Rainfall Intensity (inches/hour) 10-year, 24-hour 7.04 4 Stormwater Management Report April 6, 2023 Chavis Street Soccer Fields Pre -Development and Post -Development Drainage Areas Drainage area maps showing the drainage areas for various segments of the proposed vegetated channel are included as an attachment to this report. Note that the drainage areas are based field topography where available and GIS topography outside the limits of field topography. Erosion at Channel Outlet Flows into and out of stormwater control measures should not produce erosion for the 10-year storm. A riprap energy dissipater is used to eliminate erosion at the channel outlet. Data for the riprap dissipater is summarized below. Calculations are included in the appendix to the report. Location Length Width Thickness Riprap size Vegetated Channel outlet 60' 30" 22" NCDOT Class 1 CONCLUSION Based on the results of this analysis and design data contained in the construction drawings, we believe that the NCDEQ requirements will be met for the proposed development as a Low Density Proiect• Additional details can be found in the Appendix. APPENDICES Appendix A Drainage Area Maps Appendix B Hydrology Studio Output Appendix C Riprap Outlet Protection Calculations Appendix D Supporting Documentation APPENDIX A DRAINAGE AREA MAPS 1111-d asu MS13SON 13NNVHJ Ol-dVW VRIV 39VNIV214 56£9-5£b-6T6 VNHOM H1aON'NO1NnrNVai TESL Z JN'allinsaloy plgxo9 Od esad �nno i33ais sinVHD Hinos saaui8u3 PIP U'jnsua� am�a3»>os 3�vm N�rrveai c 6uedwoo n 3N eyj SOl31j 113JJOS 133l115 SInVHJ c APPENDIX 6 HYDROLOGY STUDIO OUTPUT Channel Report Studio Express by Hydrology Studio v 1.0.0.14 DITCH1 - Parking (North) Project filename: FWSC - Ditch Calcs.stx 04-20-2023 Channel 1 TRIANGULAR DISCHARGE Bottom Width = 0.00 ft Method = Known Q Side Slope Left, z:1 = 3.00 Known Q = 13.00 cfs Side Slope Right, z:1 = 3.00 Total Depth = 2.00 ft Invert Elevation = 425.00 ft Channel Slope = 1.000 % Manning's n = 0.033 CALCULATION SAMPLE Flow Depth Area Velocity WP n-value Crit Depth HGL EGL Max Shear Top Width (cfs) (ft) (sgft) (ft/s) (ft) (ft) (ft) (ft) (Ib/sgft) (ft) 13.00 1.19 4.25 3.06 7.53 0.033 1.04 426.19 426.34 0.74 7.14 Elev(ft) �� QII^M - Pa11rk1liii (INoi11 13) - Sects i Depth (ft) 427.50 _ ._._._._. _._._._. _._._. _. _._ _._._._. _._._._. _._._._ _._._._ _._._._. _._._._. _._._._ _._._._. _._._._. .. 2.50 427.9a .,,,,, ., ., .., . ., ..,,, ., .., . ., .., .. 2.tiC 426.5,0 ......... ......... .................................... ..................................... ... ......... ......... ....... ....... 1.50 426.64 .... ..... ..... 1.00 425.517 01.50 425.010 ............ ....................... r .......,.,.......... .......... ......,.,., .....,.,I. ......, ,.. .,. ..........,., 01.00 -1 0 1 2 3 4 5 6 7 6 9 10 11 12 13 x (ft) Channel Report Studio Express by Hydrology Studio v 1.0.0.14 DITCH2 - Parking (South) Project filename: FWSC - Ditch Calcs.stx 04-20-2023 Channel 2 TRIANGULAR DISCHARGE Bottom Width = 0.00 ft Method = Known Q Side Slope Left, z:1 = 3.00 Known Q = 26.00 cfs Side Slope Right, z:1 = 3.00 Total Depth = 2.00 ft Invert Elevation = 400.00 ft Channel Slope = 1.000 % Manning's n = 0.033 CALCULATION SAMPLE Flow Depth Area Velocity WP n-value Crit Depth HGL EGL Max Shear Top Width (cfs) (ft) (sgft) (ft/s) (ft) (ft) (ft) (ft) (Ib/sgft) (ft) 26.00 1.55 7.21 3.61 9.80 0.033 1.37 401.55 401.75 0.97 9.30 Elev (ft) DI I CII 12 - ��IiauIirfuIin (South) - S cllil t Depth (ft) 402.50 _ ._._._._. _._._._. _._._. _. _._. _._._._. _._._._. _._._._ _._._._ _._._._. _._._._. _._._._ _._._._. _._._._. .. 2.50 402.00 ............... . ............... .. ............... .. .............. .. ................ 2.00 401.50 1.50 401.00 1.00 400.50 .... 01.50 4001.010 J ............ .......... ........ 4 .......,.,., ......... .......... ......,.,., �.. -------------- I-------------- .,. ....... r,,.. ......... ........,. ....... ,,., 01.00 -1 0 1 2 3 4 5 6 7 0 9 10 11 12 13 x (ft) Channel Report Studio Express by Hydrology Studio v 1.0.0.14 DITCH 3 - Offsite (North) Project filename: FWSC - Ditch Calcs.stx 04-20-2023 Channel 3 TRAPEZOIDAL DISCHARGE Bottom Width = 3.00 ft Method = Known Q Side Slope Left, z:1 = 3.00 Known Q = 95.00 cfs Side Slope Right, z:1 = 3.00 Total Depth = 3.00 ft Invert Elevation = 400.00 ft Channel Slope = 1.000 % Manning's n = 0.033 CALCULATION SAMPLE Flow Depth Area Velocity WP n-value Crit Depth HGL EGL Max Shear Top Width (cfs) (ft) (sgft) (ft/s) (ft) (ft) (ft) (ft) (Ib/sgft) (ft) 95.00 2.06 18.91 5.02 16.03 0.033 1.85 402.06 402.45 1.29 15.36 Ellev (8) 3 ww f III III' N0 (IN C III-ffi) - SC c) III f f 1113 Depth (8) 403.00 ________ ____________ ____________ ___________ ____________ ____________ _________ ____________ ____________ ______________ ______ 3.0,0 482.58 2.50 402.010 2.O7O 401.50 .. ............................ ......... ........................ _... .............................................. ...... 1.50 401.00 ............................................ .................................................. ...... ......... 1.00 400.50 01.50 4001.010......... ..,.,., ......... ........... ............ ......... ............ ,. 01.00 -2 0 2 4 6 8 10 12 14 16 18 20 22 x (ft) Channel Report Studio Express by Hydrology Studio v 1.0.0.14 DITCH 4 - Combined (South) Project filename: FWSC - Ditch Calcs.stx 04-20-2023 Channel 4 TRAPEZOIDAL DISCHARGE Bottom Width = 4.00 ft Method = Known Q Side Slope Left, z:1 = 3.00 Known Q = 170.00 cfs Side Slope Right, z:1 = 3.00 Total Depth = 3.00 ft Invert Elevation = 400.00 ft Channel Slope = 1.000 % Manning's n = 0.033 CALCULATION SAMPLE Flow Depth Area Velocity WP n-value Crit Depth HGL EGL Max Shear Top Width (cfs) (ft) (sgft) (ft/s) (ft) (ft) (ft) (ft) (Ib/sgft) (ft) 170.00 2.53 29.32 5.80 20.00 0.033 2.31 402.53 403.05 1.58 19.18 Ellev (1t) „��) � �C - III"tll lllllne Lt ( t1(h) - Sect Clin Depth (1k) 403.00 __________ __________ _________ ___________ __________ ______ __________ ___________ __________ ________ 3.0,0 402.50 2.50 402.010 2.68 401.50 ............................ ..............................................L.... ............................ . .............................. 1.50 401.010 ----------- ------------------- ------------------- .................. ....................... ......... 1.00 400.50 .......... 01.5 4001.010 .......,.,., ...,.... ......... ..,.,.,. ......,.,.,. ...... ,. 01.00 -2 8 2 4 6 8 10 12 14 16 18 20 22 24 X (ft) APPENDIX C RIPRAP OUTLET PROTECTION CALCULATIONS CHAVIS STREET SOCCER FIELDS DESIGN OF RIPRAP OUTLET PROTECTION OUTLET FLOWRATE PIPE DIAMETER OUTLET PIPE SLOPE NUMBER OF PIPES PIPE SEPARATION ZONE FROM GRAPH PIPE AREA FLOW VELOCITY MATERIAL LENGTH WIDTH STONE DIAMETER THICKNESS 170.0 cfs 72 inches 1.00 1 0 feet 3 28.27 sq. ft. 6.0 ft/sec NCDOT Class I riprap 48.00 feet 18.00 feet 13 inches 22 inches DITCH #4 April 6, 2023 Zone Material Diameter Thickness Length Width 1 Class A 3 9 4 x D(o) 3 x D(o) 2 Class B 6 22 6 x D(o) 3 x D(o) 3 Class 1 13 22 8 x D(o) 3 x D(o) 4 Class 1 13 22 8 x D(o) 3 x D(o) 5 Class 11 23 27 10 x D(o) 3 x D(o) 6 Class 11 23 27 10 x D(o) 3 x D(o) 7 Special study required 1. Calculations based on NY DOT method - Pages 8.06.05 through 8.06.06 in NC Erosion Control Manual 2. Outlet velocity based on full -flow velocity RR W U) 15 Uj k M DIAMETER fl...) APPENDIX D SUPPORTING DOCUMENTATION NOAA PFDS RAINFALL DATA 4/20/23, 12:07 PM PF Map: Contiguous US ium i uwVa � soaldii '4) h1,t1S f„) All Ihl6;id'Ad Go,,,� noial linfolimallon NOAAATLAS 14 POINT PRECIPITATION FREQUENCY ESTIMATES: NC Data description ..... Datatype: Precipitation intensity v Units: English v Time series type: Partial duration v q iirazhrr'i Select location I''^""raNc{i.aaNnav 1)Manually: a) By location (decimal degrees, use "" for S and W): Latitude: Longitude: l .l Submit,� b) By station (list of INC stations): RALEIGH DURHAM WSFO AP (31-7069) v c) By address C _Search 0=1 -'i.trl'7W71 dN#haXlr'r,rarn � cI"halcm 2) Use map: Ifi Il ai u,�ia f iii�aui I19 r" diu rk.n .... .... Map f '%,� a) Select location Terrain ( r`� Move crosshan or double click Ill b) Click on station icon a rRuoNvaxwavd Lynchburg Show stations on map I ) d -i r ,i � � gtackohuprg�' ,Raarrake I ,fir' Narimlk t r Virginia Location information: KIngspzrl Isl ist al „ y ® ® L1eacN" Name: Morrisville, North Carolina, . USA' J ahhi n,{ ® ® ® ® Station name: RALEIGH DURHAM �� WSFOAP ® ® Site ID: 317069 1�®® )R�wy Ma<rnt Ileigh ,H®® ® ® Latitude: 3587060 Longitude: 78 78640 oon villa ® 49 ® r`IurkY ®® �� Elevation: 416 ft nll® �, ® y@t /fyotteville ® M 5 up 111 Milnrim..n bm yi A'L+451 YAItltlI J lvi[h � '10olik"i gain ✓Jr ESRI Maps QDmna -Source: USGS POINT PRECIPITATION FREQUENCY (PF) ESTIMATES WITH 90% CONFIDENCE INTERVALSAND SUPPLEMENTARY INFORMATION NOAA Atlas 14, Volume 2, Version 3 PF tabular ' Print pace u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u PDS-based precipitation frequency estimates with 90% confidence intervals (in inches/hour)1 Duration Average recurrence interval (years) 1 _ ' S 10 25 50 100 200 500 1000 5-min 4.73 (4.34- 115) 5.53 (5.08 6 04) 6.36 (5.84-6.92) 1.04 (6.47-7.67) 7.76 (7.09-8.44) 8.21 Q.51A.98) 8.12 (7.88-9.47) 9.10 (8.18-9.90) 9.50 (8 48.,10 3) 9.83 T,. 10.7) 10.min 3.78 (3.474.12) 4.43 (4.064 82) 5.09 (4.68-5.54) 5.63 (5.17-6.13) 6.18 (5.65-6.73) 6.58 (5.99-7.15) 6.93 (6.26-7.52) 7.21 (6.49-7.85) 7.52 (6 71A 18) 7,73 (6.84-8.43) iSmin 3.15 (2.89-3.43) 3.71 (3.404.04) 4.29 (3.954.68) 4.75 (4.36-5.17) 5.22 (4.77-5.68) 5.56 (5.05-0.04) 5.84 (5.28-6.34) 6.07 (5.45-6.60) 6.31 (5.63-0.87) 6.47 (5.72-7.05) 30.min 2.16 (1.98-2.35) 2.56 (2.35-2.79) 3.05 (2.80-3.32) 3.44 (3.16-3.75) 3.87 (3.534.21) 4.18 (3.814.55) 4.47 (4.044.86) 4.72 (4.25-5.14) 5.02 (4.485.46) 5.24 (4.64-5.71) 60.min 1.35 (1.24-1.47) 1611 (1.47 1 75) 1.96 (1.80-2.13) 2.24 (2.06-2.44) 2.58 (2.35-2.80) 2.84 (2.SBJ.08) 3.08 (2.78-3.35) 3.31 (2.98-3.60) 3.60 1-3 92) (3 2.... 3.83 (3.384.17) 2-hr 0.779 (0.712-0.854) 0.932 (0.853 1 02) 1.15 (1.05-1.26) 1.32 (1.20-1.45) 1.54 (1.39-1.68) 1.71 (1.54-1.87) 1.88 (1.68-2.05) 2.05 (1.82-2.23) (1 99..-2 46) .... 2.25 2,42 (2.12-2.64) 3-hr 0.550 7F (0.504-0.602) 0.658 (0.604 0.721) 0.812 (0.743-0.891) 0.944 (0.861-1.03) JL 1.11 (1.01-1.21) 1.25 (1.13-1.36) 1.38 (1.24-1.51) 1.52 11 (1.35-1.66) 1.70 IF (1.50-1 86) 1.85 (1.61-2.02) 0.333 0.399 F 0.493 0.574 0.678 0.764 0.850 0.938 1.06 1.16 6-hr (0 307 0 364) I (0 368 0 436) 1 (0; 453 0 538) (0.526-0.624) (0 617-0735) (0.692 0 828) (0 764 0 920) (0.835-1.02) (0.928-1.14) (1.00-1.25) 0.197 0.235 0.292 0.341 0.406 0.461 ..(0.463-0.556).... 0.517 0.575 0.654 0.721 12-hr (0.182-0.214) (0.218 0 256) (0.269-0.317)..., (0.314-0.371) (0.371-0.439)..., (0.417-0.497) (0.509-0.618) (0 570,,,0 703) (0.619-0.776) 0.118 0.142 F 0.178 0.206 0.243 0.273 0.303 0.334 0.375 0.408 24-hr (0.110-0.127) (0.1330153) I (0.166-0.191) (0.192-0.220) (0.226-0.261) (0.253-0.292) (0.280-0.325) (0.308-0.358) (0345 -0 404).... (0.374-0.440) 0.068 77 0.082 0.101 0.116 0.136 0.152 0.168 0.184 0.206 0.223 2-tlay (0.063-0.073) (0.0760088) (0.0.4-0.109) (0.108-0.125) (0.127-0.147) (0.141 -0.164) (0.155-0.181) (0.169-0.199) (0.189-0223) (0.204-0.241) 0.048 0.057 0.071 0.081 0.095 0106 0.118 0.129 77 0.144 0.156 3-tlay (0 045 0 051) I (0 054 0 062) 1 (0; 066 0 076) T_o76-0.087) (0 089-0,103) (0.099 0 114) (0 109 0 127) (0.119-0.139) (0.132-0.156) (0.143-0.169) 0.038 0.045 0.056 0.064 0.075 0.084 ..(0.085-0.099).... 0.092 0.101 0.114 0.123 4-day (0.035-0.041) (0.042 0 049) (0.052-0.060)..., (0.060-0.069) (0.070-0.080)..., (0.078-0.090) (0.093-0.109) (0 1040 122).... (0.112-0.133) w w.nws.noaa.gov ��rarar� l https://hdsc.nws.noaa.gov/hdsc/pfds/pfds-map_cont.html?bkmrk=nc 1 /2 4/20/23, 12:07 PM PF Map: Contiguous US 0.025 0.030 0.036 0.041 D.N. 0.054 0.059 0.065 0.072 0.078 7-day (0.024-0.027) (0.028 0 032) (0.034-0.039) (0.039-0.044) (0.045-0.051) (0.050-0.057) (0.055-0.063) (0.060-0.069) (0 067-0078) (0.072-0.084) 0.020 0.024 0.028 0.032 0.037 0.041 0.045 0.049 0.054 0.059 10-tlay (0.019-0.021) (0.022 0.025) (0.027-0.030) (0.030-0.034) (0.035-0.040) (0.038 0.044) (0.042-0.048) (0.046-0.053) 1.050 0.058) (0.054-0.063) 0.013 0.016 0.019 0.021 0.024 0 026 0.029 0.031 0.035 0.037 20-tlay (0 013 0 014) I (0 016 0 017) 1 (0; 017 0 020) (0.020-0.022) (0 022-0.025) (0.024 0 028) (0 027 0 031) (0.029-0.033) (0.032-0.037) (0.034-0.040) 0.011 0.013 0.015 0.017 0.019 0.020 ..(0.021-0.024).... 0.022 0.024 0.026 0.027 30-day (0.010-0.012) (0.012 0 014) (0.014-0.016)..., (0.016-0.018) (0.018-0.020)..., (0.019-0.022) (0.022-0.025) (0 024,,,0 028) (0.025-0.030) 0.009 0.011 0.013 0.014 0.015 0.017 0.018 0.019 0.020 0.022 45-day (0.009-0.010) (0.010 0 012) (0.012-0.013) (0.013-0.015) (0.015-0.016) (0.016-0.018) (0.017-0.019) (0.018-0.020) (0 019 -0 022).... (0.020-0.023) 0.008 0.010 0.011 0.012 0.013 0.014 0.015 0.016 0.017 0.018 60-tlay (0.008-0.009) (0.009 0.010) (0.011-0.012) (0.011-0.013) (0.013-0.014) (0.014-0.015) (0.014-0.016) (0.015-0.017) (0.016-0 018)....... (0.017-0.019) 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 ofthe 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greaterthan 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 cu rrently valid P M P values. Please refer to NOAAAdas 14 document for more information. Estimates from the table in CSV format: Precipitation frequency estimates v l Submit I US Department of Commerce National Oceanic and Atmospheric Administration National Weather Service Office of Water Prediction (OWP) 1325 East West Highway Silver Spring, MD 20910 Page Author: HDSC webmaster Page last modified. April 21, 2017 Main Link Categories: Home I OWP Map Disclaimer Privacy Policy Disclaimer About Us Credits Career Opportunities Glossary https://hdsc.nws.noaa.gov/hdsc/pfds/pfds-map_cont.html?bkmrk=nc 2/2