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Drainage Reports - 10/28/2003
atp CENTENNIAL HIGH SCHOOL EXPANSION FINAL DRAINAGE AND EROSION CONTROL REPORT B E Y 0 N D E N G I N E E R 0 N G 1 1 1 1 CENTENNIAL HIGH SCHOOL EXPANSION FINAL DRAINAGE AND EROSION CONTROL REPORT for paudechooDstr# 2407 LaPorte Avenue Ft. Collins, Colorado 80521 31 Nolte Associates, Inc. 1901 Sharp Point Drive, Suite A Fort Collins, Colorado 80525 (970) 221-2400 March 12, 2003 Revised September 9, 2003 ' September 10, 2003 FCO22701 ' Mr. Basil Hamdan City of Fort Collins Stormwater Utility ' P.O. Box 580 Fort Collins, CO 80522 1 J n BEY ON D E N G IN E E R ING RE: Centennial High School Expansion - Final Drainage and Erosion Control Report Dear Mr. Hamdan: We are pleased to resubmit the "Centennial High School Expansion - Final Drainage and Erosion Control Report " for your approval. We have incorporated the comments provided by Wes Lamarque into the drainage and erosion control plans. We have addressed these comments and made modifications to the site's detention and outfall location. This report was prepared in compliance with technical criteria set forth in the Storm Drainage Design Criteria and Construction Standards (revised January 1997) for the City of Fort Collins. If you have any questions or need further clarification, please call me at your convenience. Sincerely, NOLTE ASSAOCIATES, Inc. Thomas M. Ochwat, P.E. Project Manager NOLTE ASSOCIATES, INC. 1901 SHARP POINT DRIVE, SUITE A FORT COLLINS, CO 80525 970.221.2400 TEL 970.221.2415 FAX WWW.NOLTE.COM N:1FCO2271DrainagelW0 dTmal drainage `pt Itr20030910.dm NOL7"E Final Drainage & Erosion Control Study BEYOND ENGINEER 1 N G Centennial High School Expansion TABLE OF CONTENTS PAGE ' 1.0. INTRODUCTION.............................................................................................................I 1.1 Site Location.........................................................................................................1 1.2 Existing Site Description...................................................................................... I 1.3 Proposed Project Description................................................................................1 2.0 VICINITY MAP...............................................................................................................3 ' 3.0 METHODOLOGY............................................................................................................4 3.1 Compliance with Standards..................................................................................4 ' 3.2 Analytical Methods...............................................................................................4 4.0 HISTORIC DRAINAGE CONDITIONS.........................................................................4 ' 4.1 Major Basin Description.......................................................................................4 4.2 Floodplain.............................................................................................................4 ' 5.0 DEVELOPED DRAINAGE CONDITIONS....................................................................5 5.1 General Concept....................................................................................................5 5.2 Basin Descriptions................................................................................................5 ' 5.3 Detention/Water Quality Pond Design.................................................................6 6.0 STORM SEWER SYSTEMS...........................................................................................8 ' 6.1 General Concept....................................................................................................8 7.0 EROSION AND SEDIMENT CONTROL.......................................................................8 7.1 General Concept....................................................................................................8 7.2 Existing Site Conditions.......................................................................................8 7.3 Soils...................................................................................................................8 ' 7.4 Schedule................................................................................................................8 7.5 Construction Materials and Equipment ................................................................9 ' 8.0 CONCLUSIONS ................................................................................................................9 8.1 Drainage Concept..................................................................................................9 ' 8.2 Floodplain Variance..............................................................................................9 REFERENCES...............................................................................................................I I t Nolte Associates, Inc. N:\FCO227\Drainage\Word\Centennial_DmgRpLfinal.doc 1 1 1 t 1 1 1 Isk:)= BEYOND ENGINEERING Final Drainage & Erosion Control Study Centennial High School Expansion APPENDIX Appendix A - Historic/Developed Hydrology Appendix B - Detention/Water Quality Pond Design Appendix C - Design Charts, Tables and Graphs Appendix D - Supplemental Information BACK POCKET — Overall Drainage Plan - Grading and Erosion Control Plan Nolte Associates, Inc. N:\FCO227 Drainage\Word\Centennia]_DmgRpt_final.doc ' Final Drainage & NOLTE ' Erosion Control Study BEYOND E N G I N E E R I N G Centennial High School Expansion 1 1 1 1 i 1 t t 0 1 1 1.0 INTRODUCTION 1.1 Site Location The Centennial High School site is bounded by Laurel Street to the south, Mathews Street to the west, Peterson Street to the east and residential apartments to the north. More particularly, the Site (2.67 acres) is located in the Northwest Quarter of Section 13, Township 7 North, Range 69 West of the 6 b Principal Meridian, County of Larimer, State of Colorado (see Vicinity Map, page 3). 1.2 Existing Site Description In general, the Site slopes at one percent to the south and east towards the intersection of Laurel Street and Peterson Street. The Site's present use is public education and consists of four buildings. An old kindergarten building (presently used as the art building) is located on the west of the site along Mathews Street. There is a park area located to the east of the "Kindergarten" building and west of an auxiliary building (mobile modular building). The existing historic Laurel Elementary School building is adjacent to the auxiliary building (to the east) and is bordered by a parking lot and alley to the north. Between the Laurel Elementary School building and Peterson Street is a concrete masonry block and steel framed gymnasium. There are large trees on the grounds that border along the sidewalk adjacent to Matthews Street, Laurel Street and Peterson Street. 13 Proposed Project Description The proposed improvements of the existing Centennial High School will consist of expansion (addition of new buildings) and removal and remodel of existing structures. The intent is to maintain the historic building and significantly expand the school. New buildings will be constructed on the site and the existing gym structure and the "Kindergarten" building will be demolished. The existing historic Laurel Elementary School building will remain along with the adjacent ' Nolte Associates, Inc. 1 N:\FCO227\Drainage\Word\Centennial_DmgRpt_final.doc 1 1 1 1 NOLTE Final Drainage & BEYOND ENGINEERING Erosion Control Study Centennial High School Expansion Nolte Associates, Inc. parking area adjacent to the alley to the north. A stormwater detention facility will be designed along the south and east side of the proposed building improvements along Laurel Avenue and Peterson Street. All of the existing trees along the tree lawn between the sidewalk and street curb will remain in place. Significant consideration in minimizing the impact to the existing trees have been addressed in the site plan. 2 N:\FCO227\Drainage\Word\Centennial_DmgRpt_final.doc II it NCLTE BEYOND ENGINEERING 2.0 VICINITY MAP Final Drainage & Erosion Control Study Centennial High School Expansion WaAiingtom CF. FORT . COLLINS � (P _ f JKRY AT Dann n ti.. Project i Location URI -1 s A E13 Ira -ij --- = -.� an High Sch b�D8887 - M�l1 � � Lecher TOPO! INolte Associates. Inc. 3 N:\FCO227\Drainage\Word\Centennial_DmgRpt_final.doc Final Drainage & NOL7"E Erosion Control Study ' BEYOND ENGINEERING Centennial High School Expansion 3.0 METHODOLOGY ' 3.1 Compliance with Standards This Final Drainage & Erosion Control Study was prepared in accordance with the ' design requirements and procedures set forth in the City of Fort Collins (City) Storm Drainage Criteria and Construction Standards (Criteria — Ref. 1) and Urban Storm Drainage Criteria Manual (Manual — Ref. 2) by the Urban Drainage and Flood Control District. ' 3.2 Analytical Methods ' The Rational Method was used to calculate 2-year and 100-year developed flows. The Rational Method is widely accepted for designs involving small drainage areas (<160 acres) and short times of concentration. Mathematically, it relates peak discharge to the runoff coefficient, rainfall intensity, and drainage area. ' Runoff coefficients and rainfall intensity data were obtained from the Criteria. ' 4.0 HISTORIC DRAINAGE BASINS 4.1 Major Basin Description The Site lies within the Old Town Basin and is part of the Locust Street Outfall. The Old Town Basin Master Drainage Plan was last accepted in January of 1993. A current revision to the Old Town Basin Master Drainage Plan is in for review ' and acceptance by the City. This basin historically releases runoff into the Poudre River. 4.2 Floodplain ' The City's Storm Water Utilities Department has designated 10-yr and 100-yr floodplain areas throughout the city where storm water runoff within streets ' exceeds 200 cfs for the major storm event. Based on the 1993 Old Town Basin Master Drainage Plan, the existing and proposed structures on the project site lie ' Nolte Associates, Inc. 4 N:\FCO227\Drainage\Word\Centennial_DmgRpt_fmal.doc ' Final Drainage & NOL7"E ' BEYOND ENGINEERING Erosion Control Study Centennial High School Expansion 1 outside of the City's designated floodplain areas within Mathews Street and ' Peterson Street. However, the current revision to the Old Town Basin Master Drainage Plan reflects an increase in the floodplain areas (due to the City's update in rainfall intensities) to now encompass the Site. When this revised floodplain is adopted by City Council, the entire Site will lie within a "Moderate ' Risk Floodplain" for the 100-yr storm event. The City defines a "Moderate Risk Floodplain" as incurring floodwaters of less than one foot over the existing site ' topography. ' 5.0 DEVELOPED DRAINAGE CONDITIONS 5.1 General Concept In general, developed flow patterns from the proposed site improvements will follow the historic flow patterns. The majority of the developed basins onsite will ' sheet flow or be conveyed via a grass swale in an easterly direction to the proposed on -site detention/water quality pond located in the southeast corner of ' the site. Developed flows along the Site's west side and along Mathews Street will flow south via curb and gutter to an existing combination inlet at the intersection ' of Laurel Street and Peterson Street. Runoff from the north side of the ' improvements will enter an alley/drainageway that routes stormwater east to Peterson Street. These storm flows are then routed south along the curb and gutter ' of Peterson Street to the aforementioned inlet. ' 5.2 Basin Descriptions Basin P-1 is the West side of the proposed activities building and the north and ' west portion of the site. Storm water will sheet flow from the rooftops to scuppers and continue to sheet flow from these outfalls into the gutter on Mathews Street. The storm water will flow south on Mathews Street and east on Laurel Street Nolte Associates, Inc. 5 N:\FCO227\Drainage\Word\Centennial_D gRpt_final.doc Final Drainage & NOLTE BEYOND ENGINEERING Erosion Control Study Centennial High School Expansion along the curb and gutter to a combination inlet located on the northwest comer of ' the intersection for Peterson Street and Laurel Street. Basin P-2 is the south and east portion of existing administration building, the southern portion of the proposed administration addition and proposed activities building, and the landscape areas up to the back of walk on Laurel Street and the back of walk on Peterson Street. Storm water will sheet flow from the rooftops to ' scuppers and continue to sheet flow from the outfalls into a grass swale. The storm water will flow east to the detention pond in the southeast corner of the site. Basin P-3 is the north section of the existing administration building and the ' proposed administration addition, the south half of the alley and west half of Peterson Street. Storm water will sheet flow from the rooftops to scuppers and ' continue to sheet flow from the outfalls into the alley. The storm water will flow east onto Peterson Street and then south along the curb and gutter to the combination inlet at the intersection of Laurel Street and Peterson Street. 5.3 Detention/Water Quality Pond Design ' The proposed improvements to the school property will increase the imperviousness by approximately 18 percent. The current imperviousness is 56 ' percent, including half -streets and half -alley, while the proposed condition has been calculated at 66 percent. Per our meeting with City of Fort Collins ' Stormwater Utility on June 4, 2002, the designed future imperviousness for this area is 50% (see Old Town Master Drainage Plan). However, because this site has ' already been included in the basin (Sub -catchment 712 per Old Town MDP) the, excess imperviousness (6%) has been grandfathered into this study. The historic drainage for the site was calculated using the Rational Method for the ' 2-year and 100-year events. Currently, the site sheet flows overland to curb and Nolte Associates, Inc. 6 N:\FCO227\Drainage\Word\Centennial_DmgRpt_final.doc Final Drainage & NOL7-E Erosion Control Study BEYOND ENGINEERING Centennial High School Expansion gutter along the bordering streets. The stormwater is routed by curb and gutter to the combination inlet on the NW corner of Peterson Street and Laurel Street. A portion of the site drains to the NE (see Basin H-3) to the alley/valley pan that ' directs runoff east to Peterson Street, and continues south to the concentration point for the site, (DPI - the combination inlet on the NW corner of Peterson ' Street and Laurel Street). The 2-year historic runoff was calculated to be 3.40 cfs. This 2-year flow will be used as the allowable release rate for the detention pond for the proposed improvements. The detention pond volume was calculated utilizing Urban Drainage software (FAA Method). The existing conditions (56% imp.) warranted a volume of 0.163 ' ac-ft (7091 ft). The proposed conditions (66% imp.) would require 0.223 ac-ft (9706 ft). The school will be required to incorporate a detention volume of the difference (per our conversations with City of Fort Collins Stormwater Utility on June 4, 2002), or 0.060 ac-ft. Water quality calculations show that existing conditions (23% imp. H2 & 1-14) require a volume of 0.014 ac-ft and proposed conditions (51% imp. P2) would require 0.023 ac-ft of volume. Per the City's ' request, the detention pond will provide a water quality volume of 0.023 ac-ft. Thus a total volume for detention and water quality for the proposed ' improvements will be 0.083 ac-ft. These calculations can be found in Appendix D. Calculated 100-yr. runoff amounts for the historic and proposed conditions ' (Basins H-1, H-3, P-1 and P-3) that leave the site and concentrates at the combination inlet (Design Point 1) were compared for the potential of over - detention and a reduction to the release rate. The combined historic runoff at the ' inlet was determined to equal the combined proposed runoff (12.02 cfs) at this location. Thus, over -detention and a reduction to the release rate will not be required. ' Nolte Associates, Inc. 7 N:\FCO22Tnrainage\Word\Centennial_DmgRpt_final.doc ' Final Drainage & NOL7"E ' BEYOND ENGINEERING Erosion Control Study Centennial High School Expansion 6.0 STORM SEWER SYSTEMS ' 6.1 General Concept There are no new storm sewer systems proposed for this Site. A culvert will be located under the entrance walk on the south side of the proposed administration addition for the grass swale. An outlet structure (curb chaseway) is proposed from ' the detention/water quality pond to the existing curb and gutter on Peterson Street between existing trees. 7.0 EROSION AND SEDIMENT CONTROL ' 7.1 General Concept The Centennial High School site lies within the moderate Rainfall Erodibility Zone and the moderate Wind Erodibility Zone per the City of Fort Collins zone maps. 7.2 Existing Site Conditions ' In general, the Site slopes at one percent or less to the south and east towards the intersection of Laurel Street and Peterson Street. The Site's present use is a public ' school. Many of the areas are vegetated with grass and shrubs. The park area is well vegetated with mild slopes. The east side of the auxiliary gym is a dirt ' parking area with mild slopes to the east. ' 7.3 Soils The subsurface soils at the Site consist of an approximate 6-inch layer of ' cultivated silty topsoil, underlain by sandy lean clay, lean clay with sand, clayey sand and silty sand extending to the depths explored to the bedrock below. ' Reference the geotechnical report for more detailed information. 1 Nolte Associates, Inc. 8 N:\FCO227\Drainage\Word\Centennial_DmgRpt_final.doc L� 1 I 1 I J I 1 u NOLTE BEYOND ENGINEERING 7.4 Schedule Final Drainage & Erosion Control Study Centennial High School Expansion Inlet protection will be installed first. Demolition of existing structures and hard surfaces will occur second. Silt fencing will then be installed followed by clearing and grubbing and overlot grading for the Site. Next will be the placement of the vehicle tracking control at the construction entrance. The proposed utility and building construction will occur next. Paving and landscaping will follow subsequently. After permanent vegetation is stabilized, the inlet protection as well as the silt fence will be removed. The estimated start of construction for the site has been set for November 2002 with completion to be spring 2004. 7.5 Construction Materials & Equipment The contractor shall store construction materials and equipment on site in such a manner that the materials and equipment will not impact the flow of traffic. The Contractor shall also provide an area for maintenance and fueling of equipment in a confined area on site from which runoff will be contained and filtered prior to entering the direct street runoff. Contaminated soils from fuel spills shall follow state and local criteria for removal. 8.0 CONCLUSIONS 8.1 Drainage Concept The proposed drainage concepts presented in this study and shown on the drainage plan adequately provide for the conveyance of developed runoff for detention and water quality purposes from the proposed expansion. Water quality will be provided via grass turf swales and the detention pond in the southeast corner of the Site. This ensures that the proposed expansion will have limited negative impact to downstream conveyance facilities under the designed storms. Nolte Associates, Inc. 9 N:\FCO22TDrainage\Word\Centennial_DmgRpt_final.doc ' Final Drainage & N0L7"E ' Erosion Control Study BEYOND ENGINEERING G I N E E R I N G Centennial High School Expansion 8.2 Floodplain Variance ' Although, at the date of this submittal, the existing floodplain areas did not pose a flood risk, future city mapping indicates that this site will be within a "Moderate ' Risk Floodplain". City's Criteria for proposed building structures within a floodplain shall set the finish floor elevation 18" above the Base Flood Elevation ' (BFE) and for existing building structures to provide adequate flood proofing. In this case, the future BFE has been determined as no greater than one foot above ' existing ground topography. Thus, the proposed finish floor elevation should be set 30" (2.5 ft.) higher than existing ground. A variance request to this criteria is requested by the Poudre School District. The ' proposed finish floor elevations for the Activities Building and Administration Annex (adjacent to the existing school building) have been determined as 4887.83 and 4886.07, respectively. The corresponding ground topography beneath these structures have been estimated to be approximately 4886 and 4885, respectively. ' Street flowline elevation (along Mathews Street) in front of the main entrance to the Activities Building is 4885.90, which calculates a difference in elevation of ' 1.93 feet (23-inches). Street flowline elevation (along Laurel Street) in front of the ' main entrance to the Administration Annex Building is 4883.04, which calculates a difference in elevation of 3.03 feet (36.3-inches). In conclusion, both finish floor ' elevations have exceeded the estimated floodwater depth within the "Moderate Risk Floodplain" designation. Proposed flood proofing measures will be ' constructed at the entrances to the basement stairwells of the existing school building. Nolte Associates, Inc. 10 N-.WCO227\Drainage\Word\Centennial_DmgRpt_final.doc NCU E BEYOND ENGINEERING 1 2 3. Final Drainage & Erosion Control Study Centennial High School Expansion Storm Drainage Criteria and Construction Standards Manual, City of Fort Collins Stormwater Utility, Colorado, May 1984. Urban Storm Drainage Criteria Manual, Denver, Colorado, prepared by Wright - McLaughlin Engineers, March 1969. Old Town Basin Master Drainage Plan, prepared for City of Fort Collins, prepared by Resource Consultants & Engineers, Inc., January 1993. Nolte Associates, Inc. I I N:\FCO227\Drainagc\Word\Centennial_DmgRpLfinal.doc �I Appendix A ' HISTORIC/DEVELOPED HYDROLOGY P I I I I I I I I 1 M O N M A Q N U o rd il 0 0 i >, oioiolo 0 r- M : O �O 00 .O InlNloo n VI 1 O 1 U � , h a i O 4 inih Ni-. e � i I IMI I ^' c .a :' ;CD, o1O 3 ; , i a7 'C; iWl� �o'o;ol i O. o i i N i m I. C> ICI 1 U ry �iN 10 iM�IN� V � I 1 1 � 1 IN4OIM; v1 r 0\ i OR 1p ! N lO a iC1OI0!O N i ;O11zlO ti O O O � t j II III IIF 0 3 F e X C en;� � r � U Im ! F =2 M = N o ON U Li m O IK u z W vTfl 51 N Z. `Y E `• E e M m 6 [s 0 F " E �c niao U c G O vUi a e ^ b r b O V: v O G o 00 N 00 r r 0 r 0 0 F ti o 0 o v L c c r m= mo o a Z E rNvt� a W v O R o0 O F a U..a r rNaor Moro u t0lL ^ iL G Y r rNeo Moro vi � � U M a 0 � F Q ryO C C G G OCO L � a — u �m xzxx 0 �[ y N E E E a66 W U Nvrie ..7 F W � U ^ _ v U Oe� N OO r r 0 r 0 0 F ur ooco L � - o Z E M N ^ h arr �n 7 W d > w Oa e ovo00 aF s F z cC�* NNE U .O a N O � U o U y O Q' A U M vi N vi N vi N vi N N a � F Q W N N N O5 r OD M N N Q� 0 06 0 0 W — � a m xxss •gym^ A r _y O W U� C N O W W C N �— O W �g 0`0 O m Ol y am)W N W O N U m 3 E N m a y V W � W � t W COCL m O. .@ W W L W OJL W.0 u o O o o o O y u� �U > 0" z U. ._-:_ .:rt_x�r;-{,...ci �;.. NM�.Mp i.;,_! .�u�ar,,.. _. a., '.._ ».{ter z., L�'7�"�`.'a,�*&7{ .f--'�.yxi. �•- -' D „ .03 Calculated By: a Job Design Sturm 2 year (Historic) 8 E Y 0 N D E N G I N E E R I N G DIRECT RUNOFF Design I(ainfall -Basin Point Area of Area cc, t. CCt' A IntensityF - -- Design acres) - -run acre(s) inft - 2 3 4 5 6 8 ROUTED FLOWS Design Rainfall Point Arta of Area•CCt tr Intensity Flow (Q) (Basins) Design acre(s) tun in/hr cfs O0.year istonc� unofj 1(AI-L) 2.67 1 1.55 1 Date: 3/112003 Calculated By. GAD Design Storm 100 year (Historic) DIRECT' RUNOFF Design Rainfall Basin Point Area of Area cc, tc CCr' A Intensity Flow (Q) Design acre(s) min acres) in/hr cfs 1 (2 3 4 5 7 8 9 H-1 1 I H-1 I 0.92 0.96 9.53 0.89 7.93 `--"'.7.0035 ' H-2 2 H-2 I 0.87 0.29 28.62 0.25 4.65 - _"1:15 H-3 3 H-3 10.63 1.00 5.74 0.63 9.62 f6.; <'�> H-4 4 H-4 1 0.25 0.70 6.62 0.17 9.23 ROUTED FLOWS Design Rainfall Point Men of Area•CC, k Intensity Flow (Q) (Basins) Design acte(s) run in/hr cfs 1 -1,H-3 I 1.55 1 1.52 9.53 1 7.93 1= 4202, 4 -2, H4 1.12 1 0.42 28.62 1 4.65-1!-1:96rT f Cente®ial_Rational-Fort Collinaids 925 AM H-1 1 I H-1 I 0.92 0.96 9.53 0.89 7.93 `--"'.7.0035 ' H-2 2 H-2 I 0.87 0.29 28.62 0.25 4.65 - _"1:15 H-3 3 H-3 10.63 1.00 5.74 0.63 9.62 f6.; <'�> H-4 4 H-4 1 0.25 0.70 6.62 0.17 9.23 ROUTED FLOWS Design Rainfall Point Men of Area•CC, k Intensity Flow (Q) (Basins) Design acte(s) run in/hr cfs 1 -1,H-3 I 1.55 1 1.52 9.53 1 7.93 1= 4202, 4 -2, H4 1.12 1 0.42 28.62 1 4.65-1!-1:96rT f Cente®ial_Rational-Fort Collinaids 925 AM ROUTED FLOWS Design Rainfall Point Men of Area•CC, k Intensity Flow (Q) (Basins) Design acte(s) run in/hr cfs 1 -1,H-3 I 1.55 1 1.52 9.53 1 7.93 1= 4202, 4 -2, H4 1.12 1 0.42 28.62 1 4.65-1!-1:96rT f Cente®ial_Rational-Fort Collinaids 925 AM 1 -1,H-3 I 1.55 1 1.52 9.53 1 7.93 1= 4202, 4 -2, H4 1.12 1 0.42 28.62 1 4.65-1!-1:96rT f Cente®ial_Rational-Fort Collinaids 925 AM C E v 0 a E 0 O U oD W � M N = O N 4? U Ls. U ►Wi t�+� 7t 0 T d E W A .O z d 0. '0 _U a` m U O U I N i N i N N i N .C;I.O.I o 0 r eh 1 A rvrn w o ao 00 '00'V1,M. � t0. In kn O Q �o'00 � a O. rC'Q;N .�. O O O II II II • '0 3 •y E r � � N:NI U m F I OO d NIN�M 40. p e 001 N OO � i t ; i N r l 0 Oo U 1 i I °p °' e I oo�rnio Q I 1 I 1 C 1 I i e M kn ;v'I10100 a Ir'r� I i i fa�la w 0 :z C w w Z -u z w 0 z 0 f w m O F F •Er v�a ^� W — r N O y O� 00 I, 00 Gaz7 :. p c OO ONO N OMO F rA o—o r O a m „ Z J E � o0 0o ri a W v y 'i W Ono � O h0 .c F U o00 U C � d 0 O O O L C N C U M r h n a O � F ri � m O OCO C •v� 'p � ^ -- N M p 4 m � c aa4 om p q.. U .a O 6,v `c c �ornO W 13 •• i� N QW p o Oo W N W F cn40 o—o x a W � � F � a D F z^, c U ^ d o 0 T y O h h h U. ^ u. v n h r G L U M � a O � Q ECHO C 4 ^ A m m •C _ add. N M m Ca M O 1A to 0 N 3 v O tl1 N C N � 2 @ 3 0 0 N O N 0 O N l6 7 N ELO �a V y T N d T G> N m i2 O m iy a O) L ta) U) C O O ` �O O O U k .V N d > 0 z Job r Date: ss 3 Calculated By. JEP DIRECT RUNOFF ' Design Rainfall -Basin Point Am of Area CQ k CCr- A Intensity Flow (Q) -------- - Design acre(s) - min acre(s) HAV CIS 1 2 3 4 5 7 8 9 P-1 1 P-1 1.07 0.75 14.08 0.80 3.30 -"`2.64'.'__. P-2 2 P-2 1.12 0.56 17.03 0.63 3.01 1 P-3 3 P-3 0.56 0.78 8.91 0.44 4.02 1 ROUTED FLOWS Design Rainfall Point Area of Area•CCr k Inmmty Flow (Q) (Basins) Design acre(s) min in&r cfs 1 -1, P-3 1.63 1.24 14.08 1 3.30 2 1.12 0.63 17.03 3.01 -<:;]:88;. - 1 ALL 2.75 1.86 17.03 3.01 -='?.5.60-'''^+, Date: 3/11/2003 Calculated By: JEP Design Sto= 100 year (Proposed) DERECI'RUNOFF Design Rainfall Basin Point Area of Area CCt k CC, - A Intensity Flow (Q) Design acres) n® acre(s) in/Lr CIS 1 2 3 4 5 8 9 ROUTED FLOWS Design Rainfall Point Area of Area•CCt k Intensity Flow (Q) (Bas ns) Design acre(s) Ento in/tn CIS ] -I, P-3 1.63 1.546 9.88 7.78 `.12i02a'-• 2 1.12 0.78 Cententual_Rational-Fort CoRinc.xls 9:27 AM I 1 Appendix B DETENTION/WATER QUALITY POND DESIGN I I I I I I I I I I I Job Number: FCO22701 Date: 3/11/2003 Project #: FCO22701 Calculated By: TMO Project: Centennial H.S. Addition Basin Area 2.67 % Impervoius 56 ' Runoff Coefficient 0.58 Design Storm 100 Year One Hour Depth Peak Outflow X in 3.4 cfs Peak Inflow 12.0 cfs Maximum Volume 7091 cu-ft Minimum Volume 0 cu-ft NO B E Y O N.D__ :E N G I N E. E R I N G Q..t Qin = 0.28 k = 0.9 Qout/Qin k 0.05 1 0.1 0.97 0.2 0.93 0.3 0.9 0.5 0.85 0.75 0.8 ' Rainfall Runoff Outflow Storage Storage Graph information Time Runoff Outflow Time Intensity Volume Volume Volume Volume Minutes in/hr Ci AT kQT cu-ft ac-ft Minutes I Volume I Volume 5 9.95 4623 918 - 3705 0.09 - 5 - 4623 - 918 10 7.72 7173 1836 5337 0.12 10 7173 j 1836 15 6.52 9087 2754 6333 0.15 15 9087 2754 ' 20 5.60 10407 3672 6735 0.15 20 10407 3672 25 4.98 11568 4590 6978 0.16 25 11568 4590 30 1 -452 ( :�12599 1 :'5508 7091`. '0.16 '' 30-':''i:' '12599 45508 35 4.08 13268 6426 6842 0.16 35 13268 6426 40 3.74 13900 7344 6556 0.15 40 13900 7344 45 3.46 14467 8262 6205 0.14 45 14467 i 8262 j 50 3.23 15006 9180 5826 j 0.13 50 15006 9180 55 3.03 15484 10098 5386 0.12 55 15484 10098 60 2.86 15944 11016 4928 0.11 60 15944 11016 80 2.40 17840 14688 3152 0.07 j 80 17840 14688 100 2.10 19512 18360 1152 0.03 100 19512 18360 ' 120 1.85 20627 22032 -1405 -0.03 120 20627 22032 ' Notes: Job Number: FCO22701 -Date: 3/11/2003 Project #: FCO22701 Calculated By: TMO _Project:_ Centennial H.S. Addition Basin Area 2.75 % Impervoius 66 Runoff Coefficient 0.68 Design Storm 100 Year One Hour Depth X in Peak Outflow 3.4 cfs -Peak Inflow 12.02 cfs Volume 9706 cu-ft 'Maximum Minimum Volume 0 cu-ft _NJCqMTE B E Y OND E N G I N E.E R_1 N G Q.. `//� Gin= 0•28 k = 0.9 Qout/Qin k 0.05 1 0.1 0.97 0.2 0.93 0.3 0.9 0.5 0.85 0.75 0.8 Time Minutes Rainfall Intensity in/hr Runoff Volume Ci AT Outflow Volume kQT Storage Volume cu-ft Storage Volume ac-ft Graph information Time Minutes Runoff I Volume Outflow I Volume ' 5 9.95 5582 918 4664 0.11 5 i 5582 918 ] 0 7.72 8662 1836 6826 0.16 10 i 8662 j 1836 15 6.52 10973 ; 2754 8219 0.19 15 ! 10973 2754 ' .20 5.60 12566 ' 3672 8894 0.20 20 12566 ! 3672 25 4.98 13969 4590 9379 0.22 25 13969 4590 {"_r -3 4 521 30 i515 5080 35 4.08 16022 6426 9596 0.22 35 16022 6426 40 3.74 16785 i 7344 9441 0.22 40 16785 7344 ' 45 3.46 17470 8262 9208 ! 0.21 45 j 17470 j 8262 50 3.23 18120 9180 8940 0.21 j 50 j 18120 9180 "55 3.03 18698 10098 8600 0.20 .55 18698 10098 60 2.86 19254 11016 8238 0.19 i 60 19254 11016 80 2.40 21542 14688 6854 E 100 2.10 23562 18360 5202 0.16 j 80 21542 0.12 100 23562 : 120 1.85 24908 . 22032 2876 0.07 120 i 24908 14688 18360 22032 POND VOLUME CENTENNIAL HIGH SCHOOL DETENTION POND DETENTION POND INCREM. VOLUME ft3 CUMM. VOLUME ft CUMM. VOLUME ac-ft ELEV. AREA ftZ 4882.12 5 149 149 0.003 4882.50 1101 1404 1554 0.036 4883.00 4983 2710 4263 0.098 4883.50 5867 Water Quality Ponding Elevation & Required Volume 4882.80 1002 0.023 ' 100-Yr Ponding Elevation & Required Volume with Water Quality Volume 4883.38 3615 r N:\FCO227\Drainage\Excel\Detention.xls 0.083 Page 1 Design Procedure Form: Extended Detention.Basin (EDB) - Sedimentation Facility Sheet-1 of 3 I 1 I tM Designer:--rWA-= Company: $, Q(,TE- "Date: Project Cf�.sa,,i�1uA t i,S. Location: 1r 1. Basin Storage Volume C�XrSTIaGt Go.�D� rw►1S tN asi ss NZ 04)_ - Is - 23.00 % ..A) Tributary Area's Imperviousness Ratio .(I = 18 /.100) i "B) Contributing Watershed Area (Area) Area = 1.12 acres C) Water Quality Capture Volume (WQCV) WQCV = =0 13'`---watershed inches (WQCV =1.0' (0.91 ' 13 - 1.19' 12 + 0.78' 1)) D) Design Volume: Vol = (WQCV / 12)' Area" 1.2 Vol =0:014 .acre feet 2. Outlet Works A) Outlet Type (Check One) B) Depth at Outlet Above Lowest Perforation (H) C) Required Maximum Outlet Area per Row, (A.) D) Perforation Dimensions (enter one only): i) Circular Perforation Diameter OR ii) 2" Height Rectangular Perforation Width E) Number of Columns (nc, See Table 6a-1 For Ma)imum) F) Actual Design Outlet Area per Row (Aa) G) Number of Rows (nr) H) Total Outlet Area (Am) 3. Trash Rack — ."o%S- A) Needed Open Area: Ai = 0.5' (Figure 7 Value) " At B) Type of Outlet Opening (Check One) C) For 2", or Smaller, Round Opening (Ref.: Figure 6a): i) Width of Trash Rack and Concrete Opening (W=J from Table 6a-1 III Height of Trash Rack Screen (HTO Orifice Plate Perforated Riser Pipe XXX Other: WEIR H = feet Ao= .;`;, -';square inches D = inches, OR W = inches nc = _'. - T4 number A. = ':square inches yle nr= ("f,r.;� ..•,:.,number A", _ w ' square inches Ai = ».square inches < 2" Diameter Round =•y.= _ '. ;2" High Rectangular Other: U5 :i�i7>Ysn: inches Hrn = Fir t `<: inches Centennial_Water.Quality.xis,.EDB,.. - Design Procedure -Form: Extended Detention Basin (EDB) - Sedimentation Facility ' Sheet'l of 3 Designer: l A • 1). Company: w]nL.I&_ p.55vL. Date: Dq4 00/03 Project: M4*,,!4ikL 1k.S. .Location: I 1 1 1. Basin Storage Volume ( P&OPOUD C jm) r,oJ RA51a Pa) _ __—_A) Tributary Area's Imperviousness Ratio (i = la/ 100 ) -B) Contributing Watershed Area (Area) C) Water Quality Capture Volume (WQCV) (WQCV =1.0 " (0.91 ' 13._ 1.19 ' IZ + 0.78 - !)) D) Design Volume: Vol = (WQCV / 12) "Area' 1.2 2. Outlet Works A) OutietType (Check One) B) Depth at Outlet Above Lowest Perforation (H) C) Required Maximum Outlet Area per Row, (Ao) D) Perforation Dimensions (enter one only): i) Circular Perforation Diameter OR ii) 2"-Height Rectangular Perforation Width E) Number of Columns (nc, See Table 6a-1 For Ma)imum) F) Actual Design Outlet Area per Row (Ao) -G) Number of Rows (nr) H) Total Outlet Area (At) 3. Trash Rack A) Needed Open Area: A, = 0.5 " (Figure 7 Value) " Aa B) Type of Outlet Opening (Check One) - C) For 2", or Smaller, Round Opening (Ref.: Figure 6a): !) Width of Trash Rack and Concrete Opening (Wcoc) from Table 6a-1 ii) Height of Trash Rack Screen (HTR) Centennial_Water.Quality.xis,_EDB :_ la = 51.00 % _i-=r -zt_,'W51 Area = 1.12 acres WQCV = 02] -watershed inches Vol = acre-feet XXX Orifice Plate Perforated Riser Pipe Other: H = 0.68 feet Ao = square inches D= (3,7�inches, OR C3/41 ` W = inches J nc= t_`z inumber Ao = x7t . ;;l,�lsquare inches nr= jnumber Ac, = #VA lf_ square inches A, _ :'#VAL'llE! square inches _ ' ~ < 2" Diameter Round 2" High Rectangular Other: Wco„c = - ,.: ,•:: j inches 7 .. in. H� _ � .'.:�'z:. ,;�r:� ches Design Procedure Form: Grass Swale (GS) Sedimentation Facility Designer: Company: Date: "Project: 6,6r,a><CwAi44L Location: Ft-- GGLUas 1_2-YeariDesign Discharge (Total) Qz= 3.4 cfs ___27Year_Design Flow Velocity (Vz, 1.5.fps.Maximum) Vz = -1.00 fps 2. Swale Geometry A) Channel Side Slopes (Z, horizontal distance per unit vertical) Z = 10.00 (horizontal/vertical) B) 2-Year Design Flow Depth (Dz, 2 feet maximum) Dz = •0.6 ` +feet C) Bottom Width of Channel (B) B = tr r~Ot0 ': -feet 3. Longitudinal Slope A Froude Number F, 0.50 maximum, reduce V2 until F < 0.50 F = ; 3 „ A) .Design Slope (S, Based on Manning's n = 0.05, 0.01 Maximum) S = l . x0 005g :feetifeet B) Number of grade control structures required (number) 4. Vegetation (Check the type used or describe "Other") Dryland Grass (Must use irrigated turf grass if S >0.005 in XXX Irrigated Turf Grass semi -arid areas of Colorado) Other: 5. Outlet (Check the type used or describe "Other") InfiltrationTrench w/ Underdrain Grated Inlet XXX Other: WEIR Notes: On -site grass swales to detention area will provide a portion of the water quality. Centennial_ Water Quality:xls,.GS ....... ,..: «�..c... nn outs �:.�.<,v:wa:..ni n...•..�a�... .: I u4 rucsaQE SUBJECT I I I i F n I I I i I i I I 1 JOB NO. DESIGNED BY 91s.16:3 DATE CHECKED BY t )QIIldSJ rl I 0!Njl till II!i!IIllillll!IIII I !i --- LU6-) Ll f 114 lr I c l8t,t OlstS IFf. 1 I cl-M I Rl 06 i , I It Outlet Structure (Sidewalk Chase) Worksheet for Rectangular Channel Project Description Worksheet Outlet Structure Sidewalk -Flow Element Rectangular Channel Method Manning's Formula Solve.For Channel Depth Input Data _Mannings Coeffic --0.013 -- Slope 024600 Wit Bottom Width 1.00 ft Discharge 3.40 cis Results Depth 0.48 ft Flow Area 0.5 ft' Wetted Perimi 1.97 ft Top Width 1.00 ft Critical Depth 0.71 ft Critical Slope 0.008974 ft/ft Velocity 7.03 fits Velocity Head 0.77 it Specific Enerc 1.25 it Froude Numb, 1.78 Flow Type supercritical n:\fc02271drainage\culvertmaster\flowmaster.fm2 Nolte Associates Inc FlowMaster v6.1 [614o] 03/11/03 08:52:35 AM ®Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708.USA (203) 755-1666 Page 1 of 1 1 Appendix C DESIGN CHARTS, TABLES, AND GRAPHS 1 1 I 1 1 I 1 1 MAY 19a4 LII Table 3-3 _RATIONAL'METHOD RUNOFF'COEFFICIENTS FOR COMPOSITE ANALYSIS 'Character of Surface Streets, ParkRunoff Coefficient ing Lots,.Drives: CAsphalt................................................................................................ ............................................................................................. 0.95 Goncrete ravel................................................................................................. 0.95 0.50 Roofs.......................................................................................................... 0.95 Lawns, Sandy Soil: Flat<2% ............................................................................................. Average-2 to 74'0 0.10 .................................................................................. Steep >7%.......................................................................................... 0.15 15 0.20 Lawns, Heavy Soil: Flat<2% ................................. ........................................................... 2 to 7%.................................................................................. 0.20 SAverage teep >7%.......................................................................................... 0.25 0.35 3-4 DESIGN CRITERIA Table 3-4 RATIONAL METHOD FREQUENCY ADJUSTMENT FACTORS Storm Return Period Frequency Favor (years) C, .2to 10 1.00 11 t025 1.10 i 26 to 50 .1.20 51 to 100 1.25 Note. The product of C timeS C. shall not exceed 1.00 DRAINAGE CRITERIA MANUAL (V. 1) RUNOFF _51 .3t �- _2( _Z W c� W a 1C _Z W a O 5 W a 3 O v :2 ¢ W r- a P71 1 I a 1 .2 .3 5 10 :20 VELOCITY IN -FEET PER .SECOND FIGURE RO-1 .Estimate of Average Overland Flow Velocity for Use With the Rational Formula 06/2001 Urban Drainage and Flood Control District RO-13 1 1 i 1 1 1 1 i 1 1 1 1 1 1 1 0 � � 1 0 00 C 00 C 0 0. c 0 C)c o 0 C o ai o ti co � c c-i ci (J4/u!) A4!sua4ul N T C T c CD rmi O O N o- o; C 0 T' O' 'Citylof !Fort',Collins -Rainfaill lntens!tY-Duration-Frequency-T-able Jor using -the Rational Method (31 -minutes — 60 -minutes) -Figure"-3-:1 b Xitycof=FortCOIIIns Rainfall Intensity=Duration-Freq uengyTable -for. using*the Rational Method (5 -minutes -- *30 -minutes) __ Figure 3=1a Duration (minutes) .2-year Intensity in/hr 10-year Intensity in/hr 100-year Intensity in/hr 5.00 2.85 4.87 9.95 6.00 .2.67 4.56 9.31 7.00 2.52 4.31 8.80 8.00 2.40 4.10 8.38 9.00 2.30 3.93 8.03 -10.00 2:21 3.78 - 7.72 11.00 2.13 3.63 7.42 12.00 2.05 3.50 7:16 13.00 1.98 3.39 6.92 14:00 1.92 3.29 6.71 15.00 1.87 3.19 6.52 16.00 1.81 3.08 6.30 17.00 1.75 .2.99 6:10 18.00 1.70 .2.90 5.92 19.00 1.65 2.82 575 20.00 1.61 234 5.60 21.00 -1:56 2.67 .5 46 -22.00 1:53 2.61 5.32 23.00 1.49 2.55 5.20 24.00 1.46 2.49 5.09 25.00 1 A3 2.44 4.98 .26.00 1.40 2.39 4.87 27.00 1.37 1 .2.34 4.78 28.00 1.34 .229 4.69 29.00 1.32 2.25 4:60 30.00 1.30 2.21 4;52 1� i IJ 11 I I n, I Appendix D ' SUPPLEMENTAL INFORMATION I I I [1 I I I I L I I .OLTE a-E'Y=D•N-.D dE•N.G I N E E R I•N G MEETING MINUTES - .PROJECT: Centennial H:S. Improvements DATE: .May 159:2002 PROJ#: FCO227: _ 9m-AM `SUBJECT:__ .,Drainage ZOC: CFC Stormwater ATTENDEES: Name Thomas Ochwat Greg A. Dreeszen Glen Schlueter Wes Lamaroue DISCUSSION ITEMS: DETENTION REQUIREMENTS: —UL11pany Nolte Associates, Inc. Nolte Associates, Inc. City of Fort Collins City of Fort Collins Phone 419-1316 -419-1334 221-6700 221-6700 Minor storm will be 27year.and Major event will be 100-year. Water Quality to be provided for improved area. Detention will be required for improved impervious area that is greater than the mandated 50%. MODELING: Model the basin area that will enter the inlet at the comer of Laurel and Peterson. Check the Locust Street Outfall capacity as well as the storm pipes that will be tied into leading to the outfall. .Drainage area to incorporate half -streets and alleys. DOWNSTREAM EFFECTS: .Negative downstream effects are not allowed.. FLOODPLAIN: Buildings to be 18" above 100-yr floodplaim Existing building may be.grand fathered in. STREET CAPACITY: Top of curb during minor event Because of high curbs, street can be used in modeling a ponding area during the major event INLET CAPACITY: Check the inlet capacity to see if modifications are required. Use existing versus proposed conditions. n:1f42271do=mmtsltt mm\fc0227 minutes dmmmu 20020515.doc OLTE .B:E'7-OM-.D _E•N G 1 N:E:E>R J�N.G ,TO:- `Glen -Schlueter, CFC -DATE: May.22,2002 _Adele Wilson, : SLATEW =PA>IJLL -Greg-McGafrm,.PSD -FROM: Greg.A.Dreeszen PROJ*: Centennial (FCO227) SUBJECT: Centennial High School Improvements Detention Requirements The following provides a hydrologic and hydraulic basis for the proposed detention and water quality requirements. The existing conditions consist of three buildings, a small parking area, a park bordered by Laurel Avenue to the south, Mathews Street to the west, Peterson Street to the East and apartments and an alley to the north. There is currently no on -site detention or water -quality provided within the site. Runoff during rainfall events is captured by drywells within the site and an inlet at the NW comer of Peterson and Laurel. This runoff is routed via storm sewer to the Locust Street Outfall. The Locust.Street Outfall was designed for the existing conditions during a -major event and also provides water quality -at the outlet. The proposed improvements to the.school property will increase the imperviousness by approximately 12%. The current imperviousness is.56%, including half streets and half -alley, while the proposed condition would be near 68%.:Per our meeting on May 15,.2002, the designed f rture:imperviousness for this area is:50% (see Old Town MasterDrainage Plan). However, because this site has already been included inthe basin (Sub -catchment 712 per Old Town MDP) the excess imperviousness (6%) will be grand- fathered into this study. -The'historic drainage for the site was calculated using the Rational Method for the 2-year and 100-year events. Currently, the. site sheet flows overland to curb.and gutter along the bordering streets. The Stormwater is routed by curb and gutter to -the inlet at the NW comer of Peterson and Laurel. A portion of the site drains to the NE (see Basin H 3) .to the alley/valley pan that directs.runoff east to Peterson Street, and continues.south to -the concentration point -for the site, (DP1). The 2-year-runoff was calculated to be 3.40 cfs. -This 2 year flow 'will -be used as -.the allowable release rate for the detention pond for the proposed improvements. The detention pond volume was calculated utilizing Urban Drainage -software, Hydropon. Th eexisting conditions (56%imp) warranteda-voume of 0.15 ac-ft. The proposed conditions (68%) would require 0.20 ac-ft. The school will be required to incorporate a detention volume of the difference (per conversations on May .15, 2002), or 0.05 ac-ft. Water quality calculations show that -existing conditions (56% imp) require a volume of 0.04.ac-ft and proposed conditions (ow imp) would require 0.05 ac-ft of volume. The difference in the water quality -volume calculatio _is 0.01.ac=ft..A total volume for .detention and water quality will be ns proposed to.incorporatetthe calculated 0.06.ac=ft. n:lfcom\dOcmnattsVnmmkent=nal_darnc°R_rcq.d« MEMORANDUM (coat.) 'Page'2 'These calculations provide basis for the design of a.detention-facility within. the proposed -Centennial'High. School Improvements. If this aesign.process.is acceptable -to -the City of Fort CoIlins,_pleaseprovide documentation. 'The-final.design of the site may require more or.less 'imperviousness and will be accounted for in future -calculations that will be provide.in:a Final Drainage Report. -.If you have any suggestions or comments, please.contact'Thomas M. Ochwat or:myself - Sincerely, NOLTE ASSOCIATES, Inc. Prepared by: -Greg Dreeszen Project Engineer cc: File Centennial Reviewed by: -Thomas Ochwat, PE Project Manager -' m:\fcO227\documents\Jnemos\centennial—detention—req.doc s Y g • %BCE _Y:OJN!D '-E;N.G4iWE:E=RAIWG 'AMETING NBAUTES :PROJECT: "CentennialH:S.Improvements DATE c ' :JuneA,2002 'PROJ#: FCO227 "TIlVIE: '.10:00.AM -- =SUBJECT:..-Drainage/Floodpiafm - -LOC: --CFC-Stormwater ATTENDEES: Com an Phone asOchwat Nolte Associates, Inc. 419-1316A. Dreeszen r Nolte Associates, Inc. 419-1334 chlueter Ci of Fort Collins221-6700 amar ue -nTcrTT.ceTnW rrrxxo. Ci of Fort Collins 221-6700 DETENTION REQURUEMENTS: Methodology is acceptable to the city —see Nolte Memorandum dated May 22,.2002. MODELING: No further modeling of surrounding systems will be necessary. Need to show an impervious area .calculation for improvements from back of.curb versus existing. DOWNSTREAM.EFFECTS: No downstream effects -to date..2-year historic (existing) release rate is:acceptible (3.4.cfs) FLOODPLAIN: New. Buildings to be 18".above 100-yr1oodplain. (approximately.2.5'.above existing ground) Provide flood proofing to existing building. Flood proofing -will only be required if improvements exceed 50% of existing value of building. New flood criteria will be mapped in August. This will require .a.18".above floodplain. Currently buildings.are not infloodplain. Plans would have Wapprovedby August to'accept ctarent.criteria. STREET CAPACITY: Show no impact to existingstreet capacities. INLET CAPACITY: New inlet.not required.at comer. Additional inlet on Peterson wouldbe:acceptable:to.serve as junction for outlet of pond area to existing inlet. n:Ve0227�documansutxmoslfeo227 nrin_cfcstrmvtr 20020604.doc HYDROLOGIC:SUMMARY CENETNNIAL:HIGH'SCHOOLREMODEL AND.ADDITION ."June .14, 2002 'Impervious.Area: Existing Old Town.Master-Plan.mandates.a 50% impervious for the basin. --The existing imperviousness for the site is 56% (to be-grandfathered in) --The proposed imperviousness is 68%. -Back of curb impervious area increases by approx. 0.37..acres Historic release rate: --A 2-yr historic release will be required -.D.4 cfs is the calculated historic rate. Detention pond requirements: -The Locust Street Outfall is designed to convey runofffrom the 100-yr event considering existing conditions. -The required detention volume for existing conditions would be 0.15 ac-ft. -The.required water quality capture volume for existing conditions is approx. 0.039 ac-ft. -The proposed conditions require a pond volume of 0.20 ac-ft and WQCV of 0.046 ac-ft. -A pond would be required to detain the difference in volume.from existing conditions versus the -proposed conditions, or 0.06 ac-ft. This is the equivalent to a 50-ft by.50-ft pond with 1-ft of depth. ' Release point: -The intended release point for the site will be the south-east comer. An outfall will connectto.the existing inlet. -1 i' ?1 ' (All calculations ate ptelitnntary.and not to be used for actual design.) I m<e = zo rt 5' WALK rmmm m 7 71 - i 1 0000. I 1 1 I 1 w 1 Atf. 1 BLgG. cN 1 1 0.87 o.2s h1 1 1^ PROPERTY 90014DAR) 1 ` H-1 r 1 — 0.92 0.se 1 _ 0.77 - ,- LEGEND BARN AREA )OL[Xw BARN DERGNATION 100-W. 'C^ ' COEFFIUENT 2-W. 'CC ' FOEEENYENT BARN BOUNDARY DERGN PUNT EASDNG 1' CONTOUR EMSTING 5' CONTWR H-3 — 0.63 1.110 o.so LDGBLDG. \ BASEMENT / FF=4990.7 MAIN BUILDING A FF=5004.9 1 1 1 20.000' --/48O DRY WELL t_;- INLET FL-4984.08 UTILITY BOTRW-4977AB EASEMENT Fi:•� i 1 �pkM FACILITY 2' CHASI L WO DRY WILL ///��� V INLET FL-4984.09 BOTTOM-49J9.34 4 '_TY BOUNDARY -- el H-4 0.25 0.70 _ _ - _ TYPE 16 COMMATON _ INUT .2J _1 - _ _--_..-- BOTTOM-4978.81 1 8' COBCRETE PAN �•'�1-� � � � � � � � � � � � � � � � W. � � W. t � m m m m m m m m m m � m �.�•� W. � W. � � � � � � � � � W. � � � � � � � � � � W. s � � W. W. � W. � � W. _ _ - - RIM-4982.35 _ "�� - -- .INV_4WB.85 NW _ INV=49J8.80 NE _ __ INV 49)B,JJ 5 ___ . -------------- GTBITERLINE a i9' UBVEWAY -- 1 _ - TYPE IB COMBINATION INLET 49B1.W i CENTERLINE aF BOTTOM =4978.87 {} 20' ALLEY CENTERLNE OF 20' ALLEY I 'wt H I/ ZN m O 'J^ O O Zw Q F a DO 9, x N w z W o J Q � m w � = a co a 0 0 U o[ s 0 wJ W Z Z CL W g LL 11 t 9F SCALE NRI Y: 0 wx T& I'-x I - M.v1�1NOLTE Woo M41 M Lit to to o..mvm y r sr �ruwuv 00 (Q w In too ..mo W mM ra --1TITto � w isTail RN —mow �r e ©��e©uvmoelve0 1 �:❑0 / ) 1- `_/, PROPOSED ACTIVITY BUILDING / LEGEND X BASIN DESIGNATION %ILX yp a-K 'CC j ONFrOENT PROPOSED STORM DRAIN PIPE BASIN AREA 1W-p. 'CCI' C06BOENT _____� O O PROPOSED STORM mAIN INLET t mea tl M1 M � M BASIN BUINDARY ____ EXISTING 1' CONTOUR ADESIGN PUNT _-Y EXISTING 5' CONTOUR DRAINAGE ARROW —5124 PROPOSED 1' CONTOUR —51.w— PROPOSED 5' CONTOUR 1 I - EXISTING I I I I I EXISTING BUILDING EXISTING 1EXISTING BUILDING BUILDING I 1 -Y� - - _ ALLEY - 4985_ I " UI I TI ADMINI TIDN o,o I I I I I I= I E%IHNG scN a BUI ING -T 7 7� L P-3 0.58 an TENT N I $IPON[ \ V/ Z 0' d VJ � z w m C J O z O = a U w 'R NQ v LL U % 2 52 0 J Qw Z w Z c L r LL Z z o w 6O M1 LdLd U d a I s� JI _..__ ]00-Yr Pou l@v g-Eatiou N$ Req fired Volume = � - - _ — 4g' with Water Only Volume � /71 LAUSL AVENUE % 4883.3s 3615 0.083 _ w I :,6N.„ .61.'A.,5/.' MA ROM 600' flatl MI VA116 Cit of Fort Collins, Colorado Y6 JB wouMaP4. SI'l'L PLAN ADVISORY RRVIEO APPROVAL , AR+mm ,m tm ,.BY QL tl, HN.1 ,� OIEDF➢ B1: -� .tli-1 „e, e� We.e fiY r t/.' CKvµIIID d d �.+Ky SR RAY Mmxn IM -GG" MCI" B-e rw. a s..®uao fi' 1'sY PIPL A1E M MBNR SECTION A -A N1mn MMP.FD fin M A 016ACF InPr a^tlom .� A ru>{ wrRETE SPIN (rn.) Rraao en x N.T.S.