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Home My WebLink AboutDrainage Reports - 04/17/2003AIRES ASSOCIATES April 11, 2003 Mr. Glen Schlueter City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 Final Approved Reps Date �-��-a3 Re: Drainage Report for the CSU University Center for the Arts — Concert Hall Dear Glen, This letter report addresses existing and proposed drainage conditions for construction of a new concert hall at the above -referenced site. Introduction. The CSU University Center for the Arts will be located in the vicinity of the Colorado State University main campus, one block east of College Avenue. The project site is on the old Fort Collins High School property on Remington Avenue between Lake Street and Pitkin Street. The ultimate proposed build -out includes the concert hall, other smaller additions, renovation of the building's interior, and a 300-space parking lot. However, due to the available funding, only the concert hall will be constructed in the near future. This letter is intended to address only the interim phase of the concert hall addition. Future phases will require further investigation and more significant drainage improvements. Existing Conditions. This -site is located in the City of Fort Collins' Spring Creek Basin. The existing drainage patterns split flow to the northeast and to the southwest. The dividing line runs approximately from the northwest corner of the block (Remington Street and Pitkin Street) to the southeast corner of the block (Lake Street and Peterson Street). Drainage is primarily overland flow (grass, asphalt, curb and gutter) to the street, with the exception of an existing 12- inch diameter storm drain. The storm drain originates in a parking lot east of the building, heads west under the building, then south to a manhole in the intersection of Lake and Remington Streets. The intersection of Lake Street and Remington Street is a low point that drains to Spring Creek via a small storm sewer. This storm sewer also accepts runoff from the roof drains of the existing building. ' Due to the age and probable condition of the existing 12-inch diameter storm drain and downstream capacity limitations, the proposed improvements avoided adding any additional discharge to this pipe. Proposed Conditions. The site conditions will be impacted by the addition of approximately 0.62 acres of impervious area in the form of new roof top and sidewalks. The concert hall's roof top accounted for 0.37 acres of impervious area that will be conveyed through a roof drain system. New sidewalks and concrete areas will create an additional 0.25 acres of impervious area. To properly handle the additional stormwater, we incorporated a stormwater retention pond that will be located in the grass area north of the proposed addition. The retention pond is not an ideal solution and is only temporary. However, it was designed to effectively contain the full 100-year runoff volume from the new impervious area until a permanent detention pond and storm sewer is constructed for the ultimate build -out. Owen Ayres & Associates, Inc. Engineers/Scientists/Surveyors 3665 JFK Parkway, Building 2, Suite 200, P.O. Box 270460, Fort Collins, CO 80527 (970) 223-5556, Denver Metro (303) 572-1806, FAX (970) 223-5578 SCHLU4LI.DOC 32-0506.01 Printed on recycled paper Mr. Glen Schlueter Page Two April 11, 2003 A roof drain system has been strategically incorporated into the design of the new addition to remove runoff from the roof through 182 linear feet of 10-inch diameter PVC. It will outfall into the 0.285 acre-foot retention pond. A buried riprap pad was designed for erosion protection at the outlet of the pipe. ak 11*0Ce, u 5eol Co N seV I rffv e UO&M e- t7ala 'I- it". 'q" 0 1' -l'r ee loos rd. The pond volume was cal ulated by multiplying the new impervious area by the 100-year runoff of 3.67 inches to stor 150 ercent of the runoff volume. A pond volume of 0.285 acre-feet is required. The maximum depth of the pond will be 1.54 feet. The pond was designed to be shallow, flat, and wide to help facilitate infiltration and evaporation. Stormwater quality is naturally addressed by this approach. All disturbed and excavated areas will have new turf grass. Calculations for the runoff and pond volume are included in the Appendix. Conclusion. The proposed roof drain and retention pond will provide adequate conveyance and retention of the peak runoff increases produced by the project. The proposed pond is sized for 150 percent of the calculated 100-year runoff plus 0.3 feet of freeboard. Excess runoff would spill away from the building to Pitkin Street. The location of this pond fits well within.this site, is unobtrusive, and poses no safety hazards. If you have any questions regarding the procedures and results given in this report, please feel free to call us. Sincerely, Owen Ayres & Associates, Inc. John Batka, P.E. Project Engineer Chris Carlson, P.E. Project Manager JB/CC/sp Enclosure cc: Cass Beitler, Colorado State University Brian Fagerstrom, SLATERPAUL Architects SCHLU4L1.D0C 32-0506.01 APPENDIX I — \ I I I FtlnuiesT � — � I � e w.T°Iuri I ro>E: [ IY80DTMEOI6,IINEO � I wFww°uswes wsrnnon I�,� I u�N • I r r.wa� l ITS. noro .ww, ,D)YMRwsflMW, ry , f iEewsov°esE-osesne-ei MNLUIeIem I � slam-mE OETtltlIKUeY an ewFCTOF' I axwew�e nivFnr I seen c-iml ry -.ss,o ary I ____ I rou we nmcwsmo.��uxr mwcure wasE gnrs � I -xer �a roe�xsus ar 0 cweeu� Fr -- le rrrFFe ureeuerow onrm. I Cr)IIrR.CTOe BNLLI. LOGTE , wweclrtiurreomole - , eeFm M+anmwwoT,Es I YFM3N®lMO AE. 1POM lW.b PVt I FUTBGLtlwnwl,r ,cx✓;eaea � I TIE WATFAIIE Y°T tONHED BF£NIOHE TM9 bfkr t} 1 I Isr xnrnvm rtrw�eseECTc,ml I I k I b� ® 1` wuenrew . W M-1R 1 I Y 1 I � 1 / tlsmu rTrele¢� I R a . 1vF%jj! wm awemnreuE ay. •xcTNL Tpi. n,ro w Te. y 0 ® NQel MIME�1yFfA.lO ° /i ti- GRAPHIC SCALE >D 0 q D M tl LH FErf I HR:H - ZO 2t R L A T S R P A U L L � .ecelTeese Q aowu .............. .... ASSOCIA Engineers/Sclenflsfs/Surveyors r 1f I`r-. We L W etl rod' c14UMMIT AFMMAL e ueaEnn_��.....-. teEG®OY��'r � �x oec�Eo ev. s Mpw-, .......... UNIVERSITY CENTER FOR THE ARTS - CONCERT HALL u00 RF1A CTON STREET PORT axuN5, CO. •0523-6030 MOM.... COLORADO STATL UNIVERSITY FAMMES MANA(ZhiE r FORT COWNS, CO. OOSLVW30 vmfm A PM rh A1R; ON . AOOROIM OUMMC WOMA"M ....................... wo6rmm 1 -r CAD ..aowd ................. WC H! ..000AC9no1NC -o11.WN[M. 01[ ... EDki .............. oe® nr. o�c ...... .........__. A/rROVm R GIC sW mIc - Site Utility Plan C-101 Y!T �. iimmom -"HIRES ASSOCIATES ..ncsz- TTaII '1- i-k'�-b.re �+, s4ri.. ne�.-i-41 ileheFl"_.a.l Exi .4 na lmper✓"a.—' ldra�_ ' �, I Sri S(' _�✓ oN_rF�- Is,��a 5� �,da tk 4- �Iazi ICI s- / nFiraa. _ S'vCL G T�Q.rnoJeA = tSci 3)j�7?. L.Aa)' +- 6S1 (tn�v�� abo%�� 38'Dq g 'b� —� IJPxJ y_mL�tr✓io �` �rea t1,C)30 T:;^ e U v;ovS A rpk �;1, O aO --+- O. (� a 0 o c_ (a-7oao r,7 g, any C;- HSS�.r 2_ Ze.rO Cc4cJ\Mo.' in41'!' irG ion o� C)4-a losses Project No. Remarks Prepared by Date Project Name Checked by Date Title/Item Sheet of VOLUME CALCULATION Temporary Retention Pond - Design Development Submittal SURFACE DELTA CUM. CUM. ELEV. AREA DEPTH AREA VOLUME VOLUME VOLUME ft. sq.ft. ft. Acres Acre-feet Acre-feet Cf 4991.00 7795 7.37 0.1?9 0.214 0.022 1 961 1.37 0.250 "fl29f ' `` 0236 10265 4993.00 1500C 2.37 0.344 0.532 23160 lcocn- _ � 11 I . r7 9