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WATERVIEW EAST PRELIMINARY DRAINAGE REPORT EL PASO COUNTY, COLORADO

WATERVIEW EAST PRELIMINARY DRAINAGE REPORT EL PASO COUNTY, COLORADO PROJECT NO Prepared for: CPR ENTITLEMENTS 31 N. TEJON, SUITE 500 COLORADO SPRINGS, CO Prepared by: STANTEC
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WATERVIEW EAST PRELIMINARY DRAINAGE REPORT EL PASO COUNTY, COLORADO PROJECT NO Prepared for: CPR ENTITLEMENTS 31 N. TEJON, SUITE 500 COLORADO SPRINGS, CO Prepared by: STANTEC CONSULTING, INC 1110 ELKTON DRIVE, SUITE B COLORADO SPRINGS, CO June 21, 2017 CERTIFICATIONS Design Engineer s Statement: The attached drainage plan and report were prepared under my direction and supervision and are correct to the best of my knowledge and belief. Said drainage report has been prepared according to the criteria established by the County for drainage reports and said report is in conformity with the applicable master plan of the drainage basin. I accept responsibility for any liability caused by any negligent acts, errors or omissions on my part in preparing this report. Charlene. M. Durham, P.E. #36727 Seal Owner/Developer s Statement: I, the owner/developer have read and will comply with all of the requirements specified in this drainage report and plan. By (signature): Date: Title: Address: 31 N. Tejon, Suite 500 Colorado Springs, CO El Paso County: Filed in accordance with the requirements of the El Paso County Land Development Code, Drainage Criteria Manual Volumes 1 and 2, and the Engineering Criteria Manual, as amended. Jennifer Irvine, P.E., County Engineer / ECM Administrator Date Table of Contents PURPOSE... 4 GENERAL LOCATION & DESCRIPTION... 5 DESCRIPTION OF PROPERTY... 5 CLIMATE... 6 FLOODPLAIN STATEMENT... 6 UTILITIES & OTHER ENCUMBERANCES... 6 DRAINAGE BASINS AND SUB-BASINS... 6 MAJOR BASIN DESCRIPTION... 6 SUB-BASIN DESCRIPTION... 6 Historic Drainage Patterns... 6 Off-Site Drainage... 7 DRAINAGE DESIGN CRITERIA... 7 DEVELOPMENT CRITERIA REFERENCE... 7 HYDROLOGIC CRITERIA... 7 Rational Method... 7 Storm Sewer Design... 7 Detention Storage Criteria... 7 Waivers... 7 DRAINAGE BASINS... 8 OFFSITE BASINS... 8 EXISTING DRAINAGE ANALYSIS... 8 Big Johnson Basin... 8 Jimmy Camp Basin... 8 PROPOSED DRAINAGE ANALYSIS... 9 Big Johnson Basin... 9 Jimmy Camp Creek Basin DRAINAGE FACILITY DESIGN GENERAL CONCEPT STORM SEWER SYSTEM ON-SITE WATER QUALITY & DETENTION SUMMARY REFERENCE MATERIALS List of Figures Figure 1: Vicinity Map Figure 2: FIRM Map Figure 3: Existing Drainage Map... BACK POCKET20 Figure 4: Proposed Drainage Map... BACK POCKET Appendix A: NRCS Soil Report Appendix B: Existing Hydrology Calculations Appendix C: Proposed Hydrology Calculations Appendix D: Detention Pond & Water Quality Calculations Appendix V:\1817\active\ \Reports\Drainage\Waterview East PDR.doc 3 PURPOSE The purpose of this Preliminary Drainage Report (PDR) is to identify and present on and offsite drainage patterns, locate and identify tributary and downstream drainage features and facilities that impact the proposed site. Runoff quantities and proposed facilities have been calculated using the current City of Colorado Springs Drainage Criteria Manual (DCM). Waterview East is approximately acres and is part of the overall Waterview development, which is acres within El Paso County. This portion includes the area east of Powers Boulevard and south of Bradley Road. Of the acres, 26.1 acres will be commercial/retail and acres will be single family residential (713 lots). The site is bordered by Powers Boulevard to the west, Bradley Road to the north and undeveloped areas to the east and south. V:\1817\active\ \Reports\Drainage\Waterview East PDR.doc 4 GENERAL LOCATION & DESCRIPTION The Waterview East development site is located within 2 major drainage basins, Big Johnson Reservoir on the west and Jimmy Camp Creek on the east. Big Johnson Reservior Drainage Planning Study had originally stated that developed flows would be released into the Big Johnson Reservoir and no detention would be required as long as water quality measures were taken within the basin. However, within recent years, this is no longer the case. Detention will be required within all basins. There is currently no approved Drainage Basin Planning Study (DBPS) for Jimmy Camp. This report may be updated if/when a DBPS is approved. Design, phasing, responsibility and maintenance of any proposed improvements will be discussed in the final drainage report. Fees will be assessed and paid according to the current rates at the time of platting for each filing. Description of Property The project site is acres of vegetation, consisting of short grasses and weeds. The average slope of the site is between 3 and 8%, with a minimum slope of 1% along Powers Boulevard and a maximum of 19% through the central area and along the eastern boundary of the site. The site is composed of several different soil types. From the NRCS report in Appendix A, the site falls into the following soil types: 8 - Blakeland loamy sand (1-9%) Type A Soil 52 - Manzanst clay loam (3-8%) Type C Soil 56 - Nelson Tassel fine sandy loam (3-19%) Nelson Type B Soil, Tassel Type D Soil 86 - Stoneham sandy loam (3-8%) Type B Soil Wiley silt loam (3-9%) Type B Soil 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. V:\1817\active\ \Reports\Drainage\Waterview East PDR.doc 5 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. Climate The climate of the site is typical of a sub-humid to semiarid climate with mild summers and winters. The average temperature is 31 degrees F in the winter and 68.4 degrees in the summer. Total annual precipitation is inches. Floodplain Statement The Flood Insurance Rate Map (FIRM No C0768-F dated 3/17/99) indicates that there is no floodplain in the vicinity of the proposed site. See Figure 2: FIRM. Utilities & Other Encumberances The site is currently undeveloped and there are no known utilities on site. Drainage Basins and Sub-Basins Major Basin Description Waterview East development lies within 2 major basins, Big Johnson and Jimmy Camp Creek Drainage Basins. This project is part of the overall Waterview Development and design complies with the Amendment to the Master Drainage and Development Plan (MDDP) dated July 21, 2014 by Springs Engineering. The western third of the site drains to the Big Johnson Reservoir and will need to be detained prior to crossing under Powers Boulevard. The remainder of the site is within the Jimmy Camp Creek Basin and will also need to be detained prior to exiting the site. All developed runoff will meet El Paso County standards for water quality and discharge rates. Sub-Basin Description Historic Drainage Patterns The historic drainage patterns of the site were analyzed in the Master Development Drainage Plan for Waterview by Merrick and Company. No new historic calculations were done. V:\1817\active\ \Reports\Drainage\Waterview East PDR.doc 6 Off-Site Drainage There is one off-site basin within the Jimmy Camp Creek Basin. It is shown in the hydrology calculations for existing and proposed basins. Currently twin 42 cmp s carry the flow under Bradley Road on site. DRAINAGE DESIGN CRITERIA Development Criteria Reference The City of Colorado Springs Drainage Criteria Manual (DCM), El Paso County Engineering Criteria Manual (ECM) and Urban Storm Drainage Criteria Manual (USDCM) by Urban Drainage & Flood Control District was used in preparation of this report. Additional preliminary and final drainage plans, master development drainage plans and drainage basin planning studies used in the preparation of the report are listed in the References Section. Hydrologic Criteria Rational Method The rational method was used to determine onsite flows, as required by the current City of Colorado Springs Drainage Criteria Manual (DCM). Both the 5-year and 100-year storm events were considered in this analysis. Runoff coefficients appropriate to the existing and proposed land uses were selected for an SCS type B soil from Table 6-6 of the DCM. The time of concentration was calculated per DCM requirements. Rational Method results are shown in the Appendix B & C. USDCM spreadsheets were used to design the detention and water quality pond features. Storm Sewer Design Storm Sewer systems will be designed to the 100-year storm and checked with the 5-year storm. Inlets will be placed at sump areas and intersections where street flow is larger than street capacity. UDFCD Inlet spreadsheet will be used to determine the size of all at-grade and sump inlets. There will be two systems within the site, one which will release into the West Pond in the Big Johnson Basin and one releasing into the East Pond in the Jimmy Camp Basin. These facilities will be designed as part of the Final Drainage Report (FDR) for the site. Detention Storage Criteria This report addresses the preliminary design stage of the 2 detention/water quality features within the proposed development. Ponds and water quality was based on the UDFCD Volume 3 spreadsheet for an Extended Detention Basin. Preliminary storage volumes and outflows have been calculated for both detention facilities. A copy of these designs have been included in the appendix, as detention was not considered in the original MDDP report for the Big Johnson/Cruz Gulch Basin. Final calculations will be completed at the time of final platting for these facilities. Waivers No variances are being requested for this development. V:\1817\active\ \Reports\Drainage\Waterview East PDR.doc 7 DRAINAGE BASINS Offsite Basins There is one off site basin (OS-1) which contributes flow to the Jimmy Camp Basin of the development via twin 42 cmp s under Bradley Boulevard (Design Point A). The contributing area of the basin is acres, is currently undeveloped and generates 6.26 cfs and cfs for the minor and major storm events. Existing Drainage Analysis Big Johnson Basin There are two basins which are in the Big Johnson Basin portion of the development. Both of these basins release under Powers Boulevard via existing culverts to the Big Johnson Reservoir to the west. Basin BJD-13 (46.18 acres) is the top two-thirds of the area along Powers Boulevard and accounts for the majority of Basin BJD-13 shown in the MDDP. Flow is directed to an existing low spot located at Powers Boulevard (Design Point BJD-M) where an existing 60 cmp will release the flow into the open space on the west side of Powers and into the Big Johnson Reservoir. Flows for this basin are cfs for the 5-year storm and cfs for the 100-year storm. Basin BJD-13A (10.72 acres) is the remaining portion of the development along the Powers corridor and accounts for the remainder of the MDDP Basin BJD-13. This flow will leave the site at the southwest corner (Design Point B) where it is directed along Powers Boulevard to an existing 48 cmp directly south of the site. The existing culvert will release into the open space on the west side of Powers and reach the Big Johnson Reservoir. This basin generates 4.70 cfs and cfs for the 5 and 100-year storms. Jimmy Camp Basin There are 3 existing basins which are located within the Jimmy Camp basin for this proposed development. The offsite basin discussed previously, is also located within the Jimmy Camp Basin. The three on site basins are described below. Basin JCD-2 (9.25 acres) located at Bradley Road and the northeast corner of the site. Flows in this basin are carried within the roadside ditch and leave the site at Design Point JCD-C (Corresponds to the same design point in the MDDP). Flows for this basin are 4.96 cfs for the 5- year storm and cfs for the 100-year storm. Basin JCD-1 ( acres) covers the majority of the site in the Jimmy Camp basin between Bradley Road and the south boundary. Flow is conveyed through natural swales til it exits the site along the eastern boundary at Design Point JCD-B, which corresponds to the same MDDP design point. An existing stock pond is located just downstream of this design point. This basin generates cfs and cfs for the 5 and 100-year storms. Basin JCD-1A (20.80 acres) is located along the southern boundary of the site and exits to the south at Design Point C. Flows for this basin are 8.99 cfs for the 5-year storm and cfs for the 100-year storm. V:\1817\active\ \Reports\Drainage\Waterview East PDR.doc 8 Proposed Drainage Analysis The proposed development lies within two separate basins: Jimmy Camp Creek and the Big Johnson. The eastern two-thirds, which is located in the Jimmy Camp Creek Basin, will all head to the east towards the East Pond, where it will be intercepted prior to exiting the site. The western third of the site is all directed towards the West Pond, located along the Powers Boulevard, where flows will be detained prior to exiting the site and entering the open space/big Johnson Reservoir on the east site of the roadway. Below is a summary of the Design Points within each of these two basins. Big Johnson Basin The area within the Big Johnson Basin is approximately 46.5 acres. This area will include a portion of the commercial area and future ROW Ramp area for Powers Boulevard, both located at the northwest area of the site. Flows will all be directed via curb and gutter to various inlets through the site, where all flows will release into the West Pond, which has been designed to release flows less than historic, as the Big Johnson Reservoir no longer is able to accept any additional flows. Below is a summary of the design points within the Big Johnson Basin. Design Point AAA (Q5=3.0, Q100=8.6) consists of flow from Basins 102 and 103. Flows are combined at the intersection of Road R and Road O and continue to the south as gutter flow in Road R to DP-AAA. Design Point BBB (Q5=4.0, Q100=11.1) consists of flow from Basin 104 and DP-AAA. Flows are combined at the intersection of Road R and Road O and continue to the south as gutter flow in Road R to DP-CCC. Design Point CCC (Q5=9.2, Q100=22.2) consists of flow from Basins 106 and DP-BBB. It is anticipated that an at-grade inlet will installed to intercept these flows in Road R. Any flowby will continue south in Road R to DP-III. Design Point DDD (Q5=3.0, Q100=8.0) consists of flow from Basins 113 and 114. Flows are combined at the intersection of Road S and Road V and continue to the south as gutter flow in Road S to DP-DDD. Design Point EEE (Q5=4.4, Q100=11.5) consists of flow from Basin 115 and DP-DDD. It is anticipated that an at-grade inlet will be installed to intercept these flows. Any flowby will continue to street flow to the south in Road S to DP-FFF. Design Point FFF (Q5=2.6, Q100=9.8) consists of flow from Basins 116and 117, along with any bypass flow from the inlet at DP-EEE. Flows are combined at the intersection of Road W and Road S and continue to the south as gutter flow in Road S to DP-GGG. Design Point GGG (Q5=3.8, Q100=13.2) consists of flow from Basin 118 and DP-FFF. It is anticipated that an at-grade inlet will be needed to intercept these flows. Flowby will continue south in Road S to DP-HHH. Design Point HHH (Q5=2.4, Q100=7.9) consists of flow from Basin 119 and bypass flow from DP-GGG. Flows will continue as gutter flow in Road R to DP-III. V:\1817\active\ \Reports\Drainage\Waterview East PDR.doc 9 Design Point III (Q5=6.8, Q100=21.2) consists of flow from Basin 120, DP-HHH and bypass flow from the at-grade inlet at DP-CCC. Flows will continue south as gutter flow in Road R to DP-LLL. Design Point JJJ (Q5=0.7, Q100=2.1) consists of flow from Basin 105. Flows are combined at the intersection of Road R and Road T and continue to the south as gutter flow in Road R. Design Point KKK (Q5=4.9, Q100=9.9) consists of flow from Basins 107 and 108 and DP-JJJ. It is anticipated that an at-grade inlet will used to intercept these flows. Any flowby will continue to the west in Road M to DP-LLL. Design Point LLL (Q5=2.7, Q100=17.1) consists of flow from Basin 121 and bypass flows from DP-III and DP-KKK. An at-grade inlet will be utilized to intercept these flows. Bypass flows will continue as street flow to the west in Road M to the low point at DP-NNN. Design Point MMM (Q5=1.1, Q100=3.7) consists of flow from Basin 109. Flows are combined at the intersection of Road R and Road M and continues to the west as gutter flow in Road M to DP-OOO. Design Point NNN (Q5=4.7, Q100=12.8) consists of flow from Basins 122 and 125 along with bypass flow from DP-LLL. A sump inlet will be installed at this location in Road M to intercept the remaining street flow. This will connect with the storm system which releases into the West Pond along Powers Boulevard. Design Point OOO (Q5=6.6, Q100=15.2) consists of flow from Basins 123 and 124 along with street flow from DP-MMM. A sump inlet will be installed here to intercept the street flow on the west side of Road M. This will connect with the storm system which will release into the West Pond. Design Point PPP (Q5=2.6, Q100=8.6) consists of flow from Basin 130. This is a low point in Road L, where a sump inlet will be installed to intercept this flow. The inlet will connect to the main storm system and release into the West Pond. Design Point QQQ (Q5=1.7, Q100=6.0) consists of flow from Basin 131. This is a low point in Road L, where a sump inlet will be installed to intercept this flow. The inlet will connect to the main storm system and release into the West Pond. Design Point RRR (Q5=3.1, Q100=9.2) consists of flow from Basins 110, 111 and 126. Flows are combined at the intersection of Road L and Road O and continue to the south as gutter flow in Road L at DP-SSS. Design Point SSS (Q5=4.7, Q100=11.7) consists of flow from Basins 112 and 127 along with street flow from DP-RRR. It is anticipated that an ag-grade inlet will be installed to intercept the combined street flow. Flowby will continue south in Road L to DP-TTT. Design Point TTT (Q5=5.9, Q100=16.4) consists of flow from Basin 128 and bypass flow from DP-SSS This is a low point in Road L, where a sump inlet will be installed to intercept this flow. The inlet will connect to the main storm system and release into the West Pond. V:\1817\active\ \Reports\Drainage\Waterview East PDR.doc 10 Design Point UUU (Q5=5.7, Q100=13.7) consists of flow from Basin 129 and flowby from the inlet at DP-100. This is a low point in Road L, where a sump inlet will be installed to intercept this flow. The inlet will connect to the main storm system and release into the West Pond. Design Point West Pond (Q5=67.3, Q100=123.6) consists of all of the flow from the Big Johnson portion of the site. T
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