Final Drainage Letter Pikes Peak Community College Downtown Parking Lot Colorado Springs, Colorado Prepared for: Pikes Peak Community College 5775 South Academy Boulevard Colorado Springs, CO 80906-5422 Prepared by: Kiowa Project No. 14067 April 9, 2015
I. Location and Description The project site is located west of North Sierra Madre Street east of the Union Pacific Railroad R.O.W., between West Bijou Street to the north, and West Pikes Peak Avenue to the south. Figure 1 depicts the general location of the site. Proposed improvements include creating a gravel parking lot, for 68 passenger vehicles, from the existing gravel surface already on site. A private storm sewer system which includes a concrete drain pan, grated inlet, and associated piping will also be installed. II. Floodplain Statement The site is located outside the 100-year flood plain as shown on the Flood Insurance Rate Map number 08041C0729 F. III. Site Drainage The site lies within the Monument Creek Drainage Basin. Drainage patterns are depicted on Figure 2. These drainage patterns will be minimally effected by the proposed improvements to the site, as minor grading will be performed during construction. The proposed on-site and off-site private storm sewer improvements are also depicted on Figure 2, and include the installation of a 2 concrete drain pan, a 3 3 grated inlet (Design Point 1) and 315 LF of 15-inch storm sewer. These storm sewer improvements will be privately owned and maintained by Pikes Peak Community College. In the existing condition, runoff (Q5=2.3 cfs, Q100=6.6 cfs) sheet flows off the site at the south property line. At this point flows diverge with approximately half draining east to North Sierra Madre Street, and half draining south to West Pikes Peak Avenue. The half draining to Sierra Madre Street is collected by an existing curb inlet at the northwest corner of Sierra Madre Street and Pikes Peak Avenue. The remaining half draining south diverges at Pikes Peak Avenue with approximately half flowing east to the existing curb inlet at the northwest corner of Sierra Madre Street and Pikes Peak Avenue, and the remaining half flowing south to an existing curb inlet on the west side of Sierra Madre Street approximately two hundred feet south of Pikes Peak Avenue. In summary, an estimated 75 percent of existing runoff (Q5=1.7 cfs, Q100=5.0 cfs) from the site is collected by the existing curb inlet at the northwest corner of Sierra Madre Street and Pikes Peak Avenue, and an estimated 25 percent of existing runoff (Q5=0.6 cfs, Q100=1.6 cfs) from the site is collected by the existing curb inlet on the west side of Sierra Madre Street approximately two hundred feet south of Pikes Peak Avenue. In the developed condition, the total area tributary to the proposed 3 3 grated inlet is approximately 2.04 acres, which generates 2.3 cfs for the 5-year storm and 6.6 cfs for the 100-year storm. These flows will be conveyed offsite, by a proposed private 15-inch storm sewer, to the existing storm sewer manhole near the southeast corner of Sierra Madre Street and Pikes Peak Avenue. \14067DR.docx Kiowa Engineering Corporation
VICINITY MAP SITE Not to Scale FIGURE 1
IV. Conclusion Construction of the proposed private storm sewer improvements will result in the following: 1. Estimated flows of Q5=1.7 cfs, Q100=5.0 cfs will be removed from the existing curb inlet at the northwest corner of Sierra Madre Street and Pikes Peak Avenue, and moved downstream to the existing storm sewer manhole near the southeast corner of Sierra Madre Street and Pikes Peak Avenue. 2. Estimated flows of Q5=0.6 cfs, Q100=1.6 cfs will be removed from the existing curb inlet on the west side of Sierra Madre Street approximately two hundred feet south of Pikes Peak Avenue, and moved upstream to the existing storm sewer manhole near the southeast corner of Sierra Madre Street and Pikes Peak Avenue. 3. Existing drainage patterns will not change. 4. Site imperviousness will not be altered. 5. Flows conveyed by the existing storm sewer system in North Sierra Madre Street will be slightly altered however, there will be no impact to existing capacities. \14067DR.docx Kiowa Engineering Corporation
APPENDIX \14067DR.docx Kiowa Engineering Corporation
0 60' 120' SCALE: 1"=60' 1 PIKES PEAK COMMUNITY COLLEGE DOWNTOWN PARKING LOT DRAINAGE PLAN SOUTH 8th STREET, COLORADO SPRINGS, COLORADO LEGEND DESIGN POINT FLOW 1 DESIGN POINT DRAINAGE BASIN BOUNDARY DESIGN POINT 5 YEAR 100 YEAR Project No.: 14067 Date: April 9, 2015 Design: AWMc/NRK Drawn: Check: NRK AWMc FLOW DIRECTION 1 2.3 cfs 6.6 cfs Revisions: DRAINAGE PLAN FIGURE 2