Re: Leeward Renewable Energy Development Expansion Project Weld County Sketch Plan Drainage Report

Transcription

1 December 19, 2018 Weld County Department of Public Works 111 H Street Greeley, Colorado Re: Leeward Renewable Energy Development Expansion Project Weld County Sketch Plan Drainage Report To Whom It May Concern: This drainage letter demonstrates compliance with the Weld County Public Works Sketch Plan Drainage Report Outline, provided as Attachment 1, for two proposed substation platforms in Weld County. Leeward Renewable Energy Development, LLC (Leeward) plans to build two new substations, Panorama Substation and Mountain Breeze Substation, as part of their expansion efforts to increase the capacity of the Mountain Breeze Wind Energy Facility and the Panorama Wind Energy Facility. The proposed drainage improvements comply with the Weld County Chapter 23, Article XII and the Urban Drainage and Flood Control District s Urban Storm Drainage Criteria Manual (USDCM) requirements. Location Panorama Substation The new Panorama Substation site is located in the northeast and northwest 1/4 of Section 5, T11N, R59W and consists of a parcel of land that is approximately 3.5 acres. Specifically, the Panorama Substation is located along County Road 134, approximately a half mile west of the intersection of County Road 134 and County Road 125. The proposed location is within unincorporated Weld County along the boundary of property owned by Rudy L Wohlgemuth. The adjacent property to the north is owned by Anton P Joska. There are no major open channels, lakes, streams, irrigation or other water resource facilities within or adjacent to the proposed project site. There is an unnamed drainage which flows intermittently southeast of the location. Mountain Breeze Substation The new Mountain Breeze Substation is located in the NE 1/4 of Section 5, T11N, R58W and consists of a parcel of rangeland that is approximately 3.5 acres. Specifically, the Mountain Breeze Substation is located approximately a half mile east of the intersection between County Road 134 and County Road 111 along County Road 134. The proposed location is within unincorporated Weld County on property owned by Noel s Grasslands Ranch LLC to the north, Phillip Jason Smith to the west and O&M Harms LLC to the east and south. There are no major open channels, lakes, streams irrigation or other water resource facilities within or adjacent to the proposed project site Maroon Circle \ Suite 400 \ Centennial, CO O \ F \ burnsmcd.com

2 Weld County Department of Public Works December 19, 2018 Page 2 Location of each property is shown on Figure 1 provided in Attachment 2. Description of Property Panorama Substation The United States Geological Survey (USGS) was used to obtain 10-foot contours for the site and surrounding area and was used as a basis of analysis for the project. The site soil consists of a clay loam soil which is classified as hydrologic soil group (HSG) C according to the Natural Resource Conservation Service (NRCS). The soil map created using the Web Soil Survey by the NRCS is provided in Attachment 3. The substation location and surrounding area is native, undeveloped land with scattered vegetation used as pasture. Existing topography slopes from north to south at approximately 3%. There are no existing on-site or adjacent drainage facilities. No groundwater characterization has been accomplished to date. Mountain Breeze Substation The United States Geological Survey (USGS) was used to obtain 10-foot contours of the site and used as a basis of analysis for the project. The site soil consists of a sandy clay loam soil which is classified as HSG B according to the NRCS. The soil map created using the Web Soil Survey by the NRCS is provided in Attachment 3. The substation location and surrounding area is native, undeveloped land with scattered vegetation used as pasture. Existing topography slopes from west to east at approximately at 1%. There are no existing on-site or adjacent drainage facilities. No groundwater characterization has been accomplished to date. Major Basin Description Based on the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) Map No C0500E for Weld County, Colorado, Effective Date January 20, 2016, the project sites are located within Zone D. Zone D is an area of undetermined flood hazard. The flood hazard map is provided in Attachment 4. Offsite drainage around the Panorama Substation will have little impact on the substation property. The general direction of flow for runoff is south toward a native swale through the existing field, however most offsite flow north of the substation will be captured by the roadside ditches of County Road 134. Any offsite flow that hits the Panorama substation will be conveyed around the substation. Figure 2 in Attachment 2 presents the offsite drainage patterns around the Panorama Substation. The Mountain Breeze Substation will be impacted by offsite flow from the west, which flows toward a native swale east of the substation property. The gently sloping topography should not produce significant runoff. Any runoff impacting the site will be captured and conveyed around the site. Offsite drainage patterns impacting the Mountain Breeze Substation is shown on Figure 3 in Attachment 2.

3 Weld County Department of Public Works December 19, 2018 Page 3 General Proposed Concept To accommodate the new substation facilities, proposed additions to the sites include new gravel surfacing, concrete foundations, electrical equipment, new chain-link security fencing and gates, and a new access drive. Minimal disturbance and construction methods will be utilized to complete the improvements. The disturbance will maintain the existing topography by clearing and grubbing, excavation, and replacing to existing grade. Minor grading will be completed to install foundations for new equipment. The limits of disturbance will be maintained with sediment control logs, fence and construction fencing for the duration of the improvements. In addition, a concrete washout structure will be utilized through the duration for all concrete activities. When the improvements have been completed, the final stabilization will be installed, including aggregate surfacing on the yard and roadways and seeding and mulching on all other disturbed areas. Specific Detail Panorama Substation The Panorama Substation will convey all offsite flow around the substation and outlet the flow to maintain the natural flow of water. The existing basin for the site consists of 3.5 acres of agricultural land with a C-value for the 10-year storm event of 0.07 and a peak discharge of 0.6 cubic feet per second (cfs). The C-value for the 100-year event is 0.44 and generates a runoff of 5.9 cfs. Proposed improvements at the Panorama Substation do not increase the contributing drainage area but do increase the imperviousness of the site. The addition of gravel surfacing is assumed to cover the entire substation with minimal areas of concrete for equipment foundations. The proposed condition C-values for the 10-year and 100-year events are 0.38 and 0.61, respectively. The resulting runoff is 4.4 cfs during the 10-year event and 12.5 cfs for the 100-year event. Rational method calculations for the Panorama Substation are included in Attachment 5 and the runoff rates are shown on Figure 2 in Attachment 2. Mountain Breeze Substation The Mountain Breeze Substation will convey all offsite flow around the substation and outlet the flow to maintain the natural flow of water. The existing basin for the site consists of 3.5 acres of agricultural land with a C-value for the 10-year storm event of 0.07 and a peak discharge of 0.6 cubic feet per second (cfs). The C-value for the 100-year event is 0.44 and generates a runoff of 5.9 cfs.

4 BURNS MgDONNELL Weld County Department of Public Works December 19, 2018 Page 4 Proposed improvements at the Mountain Breeze Substation do not increase the contributing drainage area but do increase the imperviousness of the site. The addition of gravel surfacing is assumed to cover the entire substation with minimal areas of concrete for equipment foundations. The proposed condition C-values for the 10-year and 100-year events are 0.38 and 0.61, respectively. The resulting runoff is 4.4 cfs during the 10-year event and 12.5 cfs for the 100- year event. Rational method calculations for the Mountain Breeze Substation are included in Attachment 5 and the runoff rates are shown on Figure 2 in Attachment 2. Conclusion In review of the proposed improvements to the Panorama and Mountain Breeze Substations, the development was found to be compliant with the Municipal Code for Weld County Chapter 23, Article XII and the Urban Drainage and Flood Control District's Urban Storm Drainage Criteria Manual (USDCM) requirements. The development of the Panorama and Mountain Breeze Substations is dependent on the approval of the Mountain Breeze Use by Special Review (USR) Application. Upon approval of the application, design and calculations will be completed for each substation in accordance with USDCM. I hereby certify that this report for the preliminary drainage design of the Mountain Breeze Wind Energy Facility and the Panorama Wind Energy Facility was prepared by me (or under my direct supervision) in accordance with the provisions of the Weld County storm drainage criteria for the owners thereof. Joshua Lee, PE Senior Civil Engineer JLL/MDG Attachment 1: Sketch Plan Drainage Report Outline Attachment 2: Figures Attachment 3: NRCS Soils Report Attachment 4: FEMA Flood Maps Attachment 5: Rational Method Calculations

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7 Case Name: Case Number: Date: Weld County Public Works Sketch Plan Drainage Report Outline The following checklist is to be utilized as guidance, and may not be all inclusive. Other concerns not included in this checklist may arise during the review process. NOTE: A HARDCOPY OF THE DRAINAGE REPORT AND CONSTRUCTION DRAWINGS MUST BE SUBMITTED TO PUBLIC WORKS FOR REVIEW. Comment Headings Included Not Included N/A All reports shall be typed on 8-1/2 x 11 paper and bound. Drawings (24 x 36 ) shall be included as needed. The drawings shall be bound within the report or included within a pocket attached inside the back cover of the report. The report shall be a stand-alone document and therefore all important reference material, supporting documents, and calculations shall be copied and included within the report appendix. The report shall include a cover letter presenting the conceptual design for review and shall be prepared or supervised by an engineer licensed in Colorado. Only original documents sealed in ink will be accepted. The sealed report shall contain a certification sheet as follows: I hereby certify that this report for the preliminary drainage design of (Insert Name of Development) was prepared by me (or under my direct supervision) in accordance with the provisions of the Weld County storm drainage criteria for the owners thereof. The Drainage Report is stamped, signed, and dated by a registered P.E. licensed to practice in the State of Colorado. All submitted construction plan sheets are stamped, signed, and dated by a registered P.E. licensed to practice in the State of Colorado. The following items at a minimum should be discussed in the Drainage Report narrative and should be supported with maps and calculations in the Appendix. Include a copy of this checklist with the Drainage Report submittal. I. General Location and Description A. Location 1. Township, Range, Section, ¼-Section. 2. Local streets within and adjacent to the development. 3. Major open channels, lakes, streams, irrigation and other water resource facilities within and adjacent to proposed project site. 4. Names of surrounding developments including jurisdiction (municipalities). B. Description of Property 1. Area in acres. 2. Ground cover and soil types. 3. Major open channels and property ownership. 4. General project description. 5. Irrigation facilities and facility ownership information within 200 ft. of property. 6. Groundwater characteristics (where applicable). Page 1 of 3 M:\Clay\Development Checklists\Sketch Plan Drainage Report Checklist.docx

8 Case Name: Case Number: Date: II. Drainage Basins and Sub-Basins A. Major Basin Description 1. Reference to Weld County Master Drainage Plan(s) where applicable. 2. Major basin drainage characteristics. 3. Identification of all FEMA-defined 100-year floodplains and floodways affecting the property. B. Sub-Basin Description 1. Historic drainage patterns on the subject property and adjacent properties. 2. Off-site drainage flow patterns and impacts on the subject property. III. Drainage Facility Design A. General Proposed Concept 1. Proposed concept and typical drainage patterns. 2. Compliance with offsite runoff characteristics and constraints. 3. Anticipated and proposed drainage patterns. 4. Identify all requests for variance from Weld County Storm Drainage Criteria. B. Specific Detail Describe design storms and source of design storm depth information (NOAA Atlas, UDFCD Maps, etc). Drainage problems encountered and proposed solutions at specific locations. 3. Maintenance access and aspects of the proposed drainage. C. Sketch Plan Drainage Report Drawing Contents a. 2b. A General Location (Vicinity) Map shall be provided at a scale of 1 =2,000 or larger in sufficient detail to identify upstream off-site drainage areas flowing into the proposed development and general drainage patterns. Drainage Plan of the proposed development shall be provided at a scale of 1 =100 or 1 =200 on a 24 x36 drawing. The plan shall show the following information: Existing contours at a 2-ft maximum interval. Contours must extend at least 200 feet from all project boundaries or further if necessary to show upstream and downstream drainage relationships that impact the proposed development. The plans and report shall describe the horizontal and vertical datum (NGVD-29, NAVD-88, NAD83, etc) used on the plans and reconcile the differences where necessary. Property lines, existing and proposed lot lines, and existing and proposed easements. 2c. Streets with names. 2d. Existing drainage facilities, pipes, structures, irrigation facilities, and sizes. 2e. Overall drainage area boundary and sub-area boundaries. Page 2 of 3 M:\Clay\Development Checklists\Sketch Plan Drainage Report Checklist.docx

9 Case Name: Case Number: Date: 2f. Proposed flow directions using arrows. 2g. Conceptual location of storm sewers, swales, open channels, culverts, detention ponds, and other appurtenances. Identification of outfall locations and receiving waters. 2h. Location of all defined 100-year floodplains affecting the property. 2i. Any other items so noted within the Drainage Report. Page 3 of 3 M:\Clay\Development Checklists\Sketch Plan Drainage Report Checklist.docx

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11 Path: Z:\Resources\Local\Clients\KCM\ENS\Leeward\109319_MountainBreeze\ArcGIS\Geospatial\DataFiles\ArcDocs\Substations.mxd tmccarthick 12/12/2018 COPYRIGHT 2018 BURNS & McDONNELL ENGINEERING COMPANY, INC T012N R059W T011N R059W Contour M o u n t a i n B r e e z e S u b s t a t i o n Project Substation Index (50 foot interval) Intermediate (10 foot interval) 138 Depression Index (50 foot interval) Depression Intermediate (10 foot interval) Road Township and Range Section ,000 4,000 Scale in Feet Figure 1-1 Mountain Breeze and Panorama Substation Location Map Weld County, Colorado Source: USGS, Leeward Issued: 12/12/ inch = 4,000 feet Contour Interval: 10 feet ± R059W T012N R058W T012N T011N R059W T011N R058W P a n o r a m a S u b s t a t i o n T012N R058W T011N R058W

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13 > > > > > > > > > LEGEND PROPOSED LOCATION 4350 EXISTING 10' CONTOUR 5210 > > > DESIGN DRAINAGE PATH FLOW PATH OFFSITE DRAINAGE CHANNEL > > > > > > > > > 5200 PRE-DEVELOPMENT Q10 = 0.57 CFS Q100 = 5.91 CFS POST-DEVELOPMENT Q10 = 4.42 CFS Q100 = CFS DETENTION POND (IF REQUIRED) > > > > > > > > > ONSITE DRAINAGE CHANNEL COPYRIGHT 2019 BURNS & McDONNELL ENGINEERING COMPANY, INC NORTH 25' 50' SCALE IN FEET FIGURE 2 PANORAMA SUBSTATION DRAINAGE WELD COUNTY, COLORADO

14 > > > > > > > > > > > LEGEND PROPOSED LOCATION EXISTING 10' CONTOUR > > > DESIGN DRAINAGE PATH FLOW PATH ONSITE DRAINAGE CHANNEL PRE-DEVELOPMENT Q10 = 0.57 CFS Q100 = 5.91 CFS POST-DEVELOPMENT Q10 = 4.42 CFS Q100 = CFS DETENTION POND (IF REQUIRED) > > > > > > > > > > > COPYRIGHT 2018 BURNS & McDONNELL ENGINEERING COMPANY, INC. OFFSITE DRAINAGE CHANNEL 0 NORTH 25' 50' SCALE IN FEET FIGURE 3 MOUNTAIN BREEZE SUBSTATION DRAINAGE WELD COUNTY, COLORADO

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17 103 54' 3'' W Hydrologic Soil Group Weld County, Colorado, Northern Part (Panorama Substation) ' 4'' W 40 58' 0'' N Soil Map may not be valid at this scale ' 0'' N 40 57' 1'' N ' 1'' N ' 3'' W N Map Scale: 1:12,700 if printed on A landscape (11" x 8.5") sheet. Meters Feet Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS ' 4'' W Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/19/2018 Page 1 of 4

18 Hydrologic Soil Group Weld County, Colorado, Northern Part (Panorama Substation) MAP LEGEND MAP INFORMATION 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: Weld County, Colorado, Northern Part Survey Area Data: Version 13, Sep 10, 2018 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: 4, 2017 Apr 30, 2015 May The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/19/2018 Page 2 of 4

19 104 0' 34'' W Hydrologic Soil Group Weld County, Colorado, Northern Part (Mountain Breeze Substation) ' 24'' W 40 57' 49'' N 40 57' 15'' N Soil Map may not be valid at this scale ' 49'' N 40 57' 15'' N 104 0' 34'' W N Map Scale: 1:7,450 if printed on A landscape (11" x 8.5") sheet. Meters Feet Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS ' 24'' W Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/19/2018 Page 1 of 4

20 Hydrologic Soil Group Weld County, Colorado, Northern Part (Mountain Breeze Substation) MAP LEGEND MAP INFORMATION 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: Weld County, Colorado, Northern Part Survey Area Data: Version 13, Sep 10, 2018 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: 4, 2017 Apr 30, 2015 May The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/19/2018 Page 2 of 4

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23 104 0'2.00"W 41 0'26.66"N Panorama Substation Mountain Breeze Substation '28.07"W USGS The National Map: Orthoimagery. Data refreshed October, '3.39"N FLOOD HAZARD INFORMATION SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT Without Base Flood Elevation (BFE) Zone A, V, A99 With BFE or Depth Zone AE, AO, AH, VE, AR SPECIAL FLOOD HAZARD AREAS Regulatory Floodway 0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mile Zone X Future Conditions 1% Annual Chance Flood Hazard Zone X Area with Reduced Flood Risk due to Levee See Notes. Zone X OTHER AREAS OF FLOOD HAZARD Area with Flood Risk due to Levee Zone D NO SCREEN Area of Minimal Flood Hazard Zone X Effective LOMRs OTHER AREAS SCALE For information and questions about this Flood Insurance Rate Map (FIRM), available products associated with this FIRM, including historic versions, the current map date for each FIRM panel, how to order products, or the National Flood Insurance Program (NFIP) in general, please call the FEMA Map Information exchange at FEMA-MAP ( ) or visit the FEMA Flood Map Service Center website at Available products may include previously issued Letters of Map Change, a Flood Insurance Study Report, and/or digital versions of this map. Many of these products can beordered or obtained directly from the website. # Communities annexing land on adjacent FIRM panels must obtain a current copy of the adjacent panel as well as the current FIRM Index. These may be ordered directly from the Flood Map Service Center at the number listed above. " N Map Projection: GCS, Geodetic Reference System 1980; Vertical Datum: No elevation features on this FIRM For information about the specific vertical datum for elevation features, datum conversions, or vertical monuments used to create this map please see the Flood Insurance Study(FIS) Report for your community at Basemap information shown on this FIRM was provided in digital format by USDA, Farm Service Agency (FSA). This information was derived from NAIP, dated April 11, This map was exported from FEMA's National Flood Hazard Layer (NFHL) on 12/19/ :24:30 PM and does not reflect changes or amendments subsequent to this date and time. The NFHL and effective information may change or become superseded by new data over time. For additional information, please see the Flood Hazard Mapping Updates Overview Fact Sheet at WELD COUNTY, COLORADO AND INCORPORATED AREAS PANEL For community and countywide map dates refer to the Flood Insurance Study Report for this jurisdiction. To determine if flood insurance is available in this community, contact your Insurance agent or call the National Flood Insurance Program at NATIONAL FLOOD INSURANCE PROGRAM FLOOD INSURANCE RATE MAP 1 inch = 2,000 feet 0 1,000 2, ,000 1,260 1:24,000 6,000 Meters 1,680 8,000 Feet 500 OF Panel Contains: COMMUNITY WELD COUNTY COLORADO 2205 NUMBER PANEL 0500 This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below. The basemap shown complies with FEMA's basemap accuracy standards This map image is void if the one or more of the following map elements do not appear: basemap imagery, flood zone labels, legend, scale bar, map creation date, community identifiers, FIRM panel number, and FIRM effective date. Area of Undetermined Flood Hazard Zone D Channel, Culvert, or Storm Sewer GENERAL STRUCTURES Levee, Dike, or Floodwall B 8 OTHER FEATURES NOTES TO USERS Cross Sections with 1% Annual Chance Water Surface Elevation Coastal Transect Coastal Transect Baseline Profile Baseline Hydrographic Feature Base Flood Elevation Line (BFE) Limit of Study Jurisdiction Boundary MAP NUMBER 08123C0500E EFFECTIVE DATE 01/20/2016

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27 Designer: Mark Gonzales Version 2.00 released May 2017 Select UDFCD location for NOAA Atlas 14 Rainfall Depths from the pulldown list OR enter your own depths obtained from the NOAA website (click this link) Company: Burns & McDonnell t 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr C L t Computed t. t t 5 (urban) Date: 12/20/2018 Cells of this color are for required user-input S t 10 (non urban) 1-hour rainfall depth, P1 (in) = Project: Mountain Vista Cells of this color are for optional override values a b c Location: Weld County, Colorado Cells of this color are for calculated results based on overrides Rainfall Intensity Equation Coefficients = I / a P t L L L Regional t b t 60K S 60V 26 17i Selected t 60 14i 9 S max t, min Computed t, Regional t Q CIA Subcatchment Name Area (ac) NRCS Hydrologic Soil Group Percent Imperviousness Runoff Coefficient, C 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr Overland U/S Elevation Flow Length (ft) L i (ft) (Optional) D/S Elevation (ft) (Optional) Overland Flow Slope S i (ft/ft) Overland Flow Time t i (min) Calculation of Peak Runoff using Rational Method Overland (Initial) Flow Time Channelized (Travel) Flow Time Time of Concentration Channelized U/S Elevation Flow Length (ft) L t (ft) (Optional) D/S Elevation (ft) (Optional) Channelized Flow Slope S t (ft/ft) NRCS Conveyance Factor K Channelized Flow Velocity V t (ft/sec) Channelized Flow Time t t (min) Computed t c (min) Regional t c (min) Selected t c (min) Rainfall Intensity, I (in/hr) Peak Flow, Q (cfs) 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr Mountain Breeze Substation (Pre- Development) 3.50 B Panorama Substatation (Pre Development) 3.50 B

28 Designer: Mark Gonzales Version 2.00 released May 2017 Select UDFCD location for NOAA Atlas 14 Rainfall Depths from the pulldown list OR enter your own depths obtained from the NOAA website (click this link) Company: Burns & McDonnell t 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr C L t Computed t. t t 5 (urban) Date: 12/20/2018 Cells of this color are for required user-input S t 10 (non urban) 1-hour rainfall depth, P1 (in) = Project: Mountain Vista Cells of this color are for optional override values a b c Location: Weld County, Colorado Cells of this color are for calculated results based on overrides Rainfall Intensity Equation Coefficients = I / a P t L L L Regional t b t 60K S 60V 26 17i Selected t 60 14i 9 S max t, min Computed t, Regional t Q CIA Subcatchment Name Area (ac) NRCS Hydrologic Soil Group Percent Imperviousness Runoff Coefficient, C 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr Overland U/S Elevation Flow Length (ft) L i (ft) (Optional) D/S Elevation (ft) (Optional) Overland Flow Slope S i (ft/ft) Overland Flow Time t i (min) Calculation of Peak Runoff using Rational Method Overland (Initial) Flow Time Channelized (Travel) Flow Time Time of Concentration Channelized U/S Elevation Flow Length (ft) L t (ft) (Optional) D/S Elevation (ft) (Optional) Channelized Flow Slope S t (ft/ft) NRCS Conveyance Factor K Channelized Flow Velocity V t (ft/sec) Channelized Flow Time t t (min) Computed t c (min) Regional t c (min) Selected t c (min) Rainfall Intensity, I (in/hr) Peak Flow, Q (cfs) 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr Mountain Breeze Substation (Post- Development) Panorama Substatation (Post- Development) 3.50 B B

29 Precipitation Frequency Data Server Page 1 of 4 NOAA Atlas 14, Volume 8, Version 2 GROVER 10 W Station ID: Location name: Grover, Colorado, USA* Latitude: , Longitude: Elevation: Elevation (station metadata): 5082 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) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1.11 ( ) 1.29 ( ) 1.51 ( ) 1.71 ( ) 1.89 ( ) 2.04 ( ) 2.36 ( ) 2.64 ( ) 3.46 ( ) 4.15 ( ) 5.03 ( ) 5.78 ( ) ( ) ( ) ( ) ( ) ( ) 1.06 ( ) 1.15 ( ) 1.32 ( ) 1.52 ( ) 1.75 ( ) 2.01 ( ) 2.19 ( ) 2.35 ( ) 2.71 ( ) 3.02 ( ) 3.94 ( ) 4.71 ( ) 5.71 ( ) 6.57 ( ) ( ) ( ) ( ) ( ) 1.17 ( ) 1.39 ( ) 1.50 ( ) 1.71 ( ) 1.95 ( ) 2.20 ( ) 2.52 ( ) 2.71 ( ) 2.87 ( ) 3.28 ( ) 3.65 ( ) 4.70 ( ) 5.60 ( ) 6.77 ( ) 7.78 ( ) ( ) ( ) ( ) 1.14 ( ) 1.42 ( ) 1.69 ( ) 1.83 ( ) 2.08 ( ) 2.34 ( ) 2.60 ( ) 2.96 ( ) 3.17 ( ) 3.33 ( ) 3.77 ( ) 4.18 ( ) 5.33 ( ) 6.31 ( ) 7.59 ( ) 8.71 ( ) ( ) ( ) 1.09 ( ) 1.44 ( ) 1.80 ( ) 2.15 ( ) 2.35 ( ) 2.65 ( ) 2.93 ( ) 3.21 ( ) 3.61 ( ) 3.82 ( ) 3.99 ( ) 4.46 ( ) 4.90 ( ) 6.16 ( ) 7.25 ( ) 8.66 ( ) 9.89 ( ) ( ) 1.05 ( ) 1.28 ( ) 1.69 ( ) 2.12 ( ) 2.55 ( ) 2.80 ( ) 3.15 ( ) 3.43 ( ) 3.72 ( ) 4.14 ( ) 4.35 ( ) 4.52 ( ) 5.01 ( ) 5.47 ( ) 6.79 ( ) 7.93 ( ) 9.42 ( ) 10.7 ( ) ( ) 1.22 ( ) 1.49 ( ) 1.96 ( ) 2.47 ( ) 2.98 ( ) 3.28 ( ) 3.70 ( ) 3.97 ( ) 4.26 ( ) 4.69 ( ) 4.91 ( ) 5.08 ( ) 5.57 ( ) 6.03 ( ) 7.41 ( ) 8.59 ( ) 10.1 ( ) 11.5 ( ) 1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS) ( ) 1.41 ( ) 1.71 ( ) 2.25 ( ) 2.85 ( ) 3.45 ( ) 3.81 ( ) 4.30 ( ) 4.55 ( ) 4.86 ( ) 5.27 ( ) 5.49 ( ) 5.66 ( ) 6.15 ( ) 6.61 ( ) 8.02 ( ) 9.23 ( ) 10.8 ( ) 12.2 ( ) 1.14 ( ) 1.67 ( ) 2.04 ( ) 2.66 ( ) 3.39 ( ) 4.13 ( ) 4.59 ( ) 5.16 ( ) 5.38 ( ) 5.70 ( ) 6.07 ( ) 6.30 ( ) 6.47 ( ) 6.93 ( ) 7.38 ( ) 8.80 ( ) 10.0 ( ) 11.6 ( ) 13.0 ( ) 1.29 ( ) 1.88 ( ) 2.30 ( ) 2.99 ( ) 3.84 ( ) 4.68 ( ) 5.22 ( ) 5.88 ( ) 6.06 ( ) 6.38 ( ) 6.71 ( ) 6.93 ( ) 7.11 ( ) 7.53 ( ) 7.97 ( ) 9.38 ( ) 10.6 ( ) 12.2 ( ) 13.5 ( ) 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 12/12/2018

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