Loading...
HomeMy WebLinkAboutDrainage Reports - 03/16/2004Find roved Report _Date 3 /� PINE STREET LOFTS FT. COLLINS, COLORADO DRAINAGE & EROSION CONTROL REPORT MARCH 5, 2004 PREPARED FOR: P.V.C. REDEVELOPMENT, LLC 1 708 WALNUT STREET BOULDER, CO 80302 PREPARED BY: WELSCH DESIGN CONSULTANTS; INC. 1 708 WALNUT STREET BOULDER, CO 80302 303-447-0833 PROJECT No. 270 415� lot Kb ' ONAL &k r. PINE STREET LOFTS DRAINAGE & EROSION CON I ROL Ri.,:iow, TABLE OF CONTENTS GENERAL LOCATION & DESCRIPTION 2 DRAINAGE BASINS AND SUB -BASINS 2 DRAINAGE DESIGN CRITERIA 2 DRAINAGE FACILITY DESIGN 2 WATER QUALITY & EROSION CONTROL 4 FA.I r jrj:Akjj9] k, p WELSCH DESIGN CONSULTANTS, INC. PINE STREET LOWS DRAINAGE- & EROSION CONTROL. REPORT' GENERAL LOCATION AND DESCRIPTION The site is located in the Old Town area of the Ft. Collins at 251-253 Pine St. Specifically, the site is a triangular -shaped lot bounded on the northeast by Jefferson St., the southeast by Pine St. and the west by an alley. Currently, the site is developed and is currently vacant and owned by the Poudre Valley Creamery Co. The existing improvements on and immediately around the site are comprised entirely of building structures and pavement. DRAINAGE BASINS AND SUB -BASINS The site is located in the Old Town basin and Stormwater Inventory Map #8G. The existing topography around the site (the existing building occupies almost the entire property) slopes to the north and northeast at grades of less than 1 %. Stormwater runoff from the site ultimately flows to the Poudre River located approximately 0.25 miles northeast of the site. There are no offsite flows onto this property. A small portion of the existing parking lot and building on the west side of the alley drains east to the alley and then north to Jefferson St. The site is not located in the floodplain per the City of Ft. Collins and FEMA floodplain maps. Copies of these maps are included in the appendix. DRAINAGE DESIGN CRITERIA All drainage improvements are designed per the City of Ft. Collins stormwater drainage requirements. All existing drainage patterns around the site are maintained with the proposed improvements. The existing site imperviousness is grandfathered in per the Stormwater Utility Department's comments dated January 2, 2003. DRAINAGE FACILITY DESIGN The alley pavement is currently in poor condition and in many areas runoff drains to the edge of the existing creamery building rather than down the center of the alley. For these reasons, the alley pavement will be reconstructed with an inverted crown to convey runoff down the center of the alley and away from the proposed and existing buildings that border the alley. Existing curb grades on the southwest side of Jefferson St. convey runoff to an existing curb inlet located in a sump approximately 75 feet northwest of the centerline of Pine St. Field observations indicate that this inlet only receives drainage from the area located between the Pine St. and the alley intersections with Jefferson St. Runoff on Jefferson St. northwest of the alley and southeast of Pine St. flow away from the site. This inlet drains into a 15" pipe that flows WELSCH DESIGN CONSULTANTS, INC. 2 PINE STREET LOFTS DRAINAGE. far E RO'510N CON..I ROL R[:C:'Ofz r southeast into an existing manhole located off the northeast corner of the property. Pine St. runoff currently drains into a system of grate and curb inlets located on either side of the street. There are two grate -top surface inlets on the northwest side of Pine St. The first is located at the intersection of the alley and Pine St. A 12" pipe flows into it from an inlet on the opposite side of Pine St. and a 15" pipe flows into it from the southwest. The outflow pipe is a 15" pipe that flows to the second grate -top surface inlet located approximately 40 feet southwest of the Jefferson St. flowline. This inlet also has a 12" flowing into it from an inlet on the opposite side of Pine St. These flows exit the second inlet via a 20" pipe that flows to the manhole mentioned above and then continues to the northeast across Jefferson St. A curb & gutter inlet will be added to the 15" pipe at the south corner of the property to collect runoff that will gather at a low point that will be created by the proposed curb improvements to Pine St. Another curb & gutter inlet will be added at the northwest corner of the reconstructed parking bay where another sump will be created with the proposed improvements. This inlet will tie into the existing inlet that currently receives flows from this area via a chase drain in the existing median. The chase drain will be removed with the construction of the proposed improvements and the existing grate inlet at that location will be replaced with a manhole since it will no longer receive runoff flows with the proposed improvements. City Staff commented that the City requires one foot of freeboard from any entrance to a major drainage way. This comment was directed at the proposed garage entrance onto the alley. The concern is that the proposed curb improvements on Pine Street may create a flood routing problem at the intersection of the alley and Pine St. and potentially result in runoff reaching the garage entrance. The proposed improvements will not be able to meet the requirement of 1 foot of freeboard, but analysis of the drainage in the area indicates that this will not present a problem with the garage. The high point in the alley is the top of the concrete apron at the invert of the alley at Pine Street. This point is also the high point of the drainage basin that drains through the alley to Jefferson. The elevations • of the proposed reconfiguration of the alley at the access point to Pine Street will route any excess storm water flows through Pine St. and not down the alley. The combined effect of these conditions results in a very minimal amount of runoff in the alley at the point where the garage access ties into the alley. We currently are providing 0.41 feet of freeboard from the conveyance in Pine St. to the high point at the south end of the alley where it intersects with Pine Street. This is measured from the top of the alley apron (Elev. 4977.00) to the high point on the proposed curb island (Elev. 4976.59) which is the point where any ponding flows at the alley entrance will route and continue down Pine Street. The entrance point to the underground parking garage is slightly north of the high point and is 0.11 feet below the high point in the alley (Elev. 4976.89). Pine Street experiences very limited 100-yr flows (=2.47 cfs) and we feel that a variance from WELSC9 t DESIGN CONSULTANTS, INC. 3 PINE STREET LOFTS DRAINAC. . s` Et4C)SIpN CC) N`I ROL. RLPOIF V the one foot requirement is justified given the minimal flows within Pine Street and that the existing grades do not allow much relief from a drainage standpoint. The solid garage door is set at the highpoint of the driveway access and drainage of the exposed drive will flow towards the alley. We are reconstructing the entire alley from Pine St. to Jefferson St. The existing alley slopes into the existing building on our site. The new alley will be constructed with an inverted crown to provide positive drainage to Jefferson St., which does not currently exist. We request a variance for the one foot freeboard requirement given the limited flows that both Pine St. and the alley will experience and that we are improving the existing drainage through the alley overall. Runoff flows from the building roof drains will be distributed around the site. The roof drains on the Pine St. side of the building will be collected in a pipe inside the garage. This pipe will also receive a small amount of runoff from the small portion of the garage entrance drive that is uncovered and will be tied into the proposed manhole above the crowns of the existing pipes to guard against surcharges into the garage. The purpose of collecting the Pine St. roof drains in this pipe is to eliminate point -discharge flows across the wide proposed plaza area along the Pine St. frontage of the building. Roof drain flows along the alley and Jefferson St. will discharge to the pavement. WATER QUALITY & EROSION CONTROL The proposed improvements include landscaped areas in the Pine St. right-of- way. These areas will be curbed to minimize erosion and will also have a small positive effect on the imperviousness of the site, which is currently completely hardscaped. Nuisance flow such as snow melt from automobiles in the parking garage will be collected by an inlet and routed through a sand and oil interceptor that is connected to the building's sanitary sewer service. This is an "in -fill" redevelopment and the proposed site layout does not allow enough space to provide a 40-hour water quality extended detention pond. However, the design features listed above will improve the quality of the runoff from the site over the existing conditions. Given these circumstances, a variance is requested to waive the 40-hour water quality extended detention pond requirement. Wind and Rainfall Erosion Control The site is less than 1 acre (12,576 SF) in size and is therefore exempt from the wind erosion control requirements. The site is in an urban area and is completely surrounded by existing pavement. The existing building on site will be demolished and the new building will encompass virtually the entire property. Once the existing building is demolished, the site will be excavated for the construction of the new building which has an underground parking garage. Due to the fact that the entire site is being excavated below the street grades around the site, it is very unlikely that there WELSCH DESIGN CONSULTANTS, INC. 4 PINE STREET LOFTS DRAINAGE & Ff' OSION CON ..I..Rcn. RLP(_)R.1., will be any erosion runoff from the site during rain events. In addition, the demolition and excavation of the site is expected to take a very short amount of time. For these reasons and the site's very small size, a waiver from the standard rainfall erosion control calculations is requested. There are some street improvements proposed around the perimeter of the site which include the installation of two curb inlets on Pine St. Those inlets and the existing curb inlet on Jefferson St. may experience a small amount of erosion runoff during construction. However, the Pine St. inlets are being installed adjacent to the existing pavement and Jefferson St. is not expected to be disturbed except for the replacement of the curb across the frontage of the property. Therefore, very little erosion runoff is anticipated to these inlets during construction. If erosion runoff does become a problem during construction, gravel curb inlet filters will be installed per the City of Fort Collins standards. WELSCH DESIGN CONSULTANTS, INC. 5 PINE STREET LOFTS DRAINAGEr & EF?osioN CoNrizoi- REPOR!' APPENDIX WELSCH DESIGN CONSULTANTS, INC. LLI I-L w ((NIVO 1 f A jcg 4, Uj) HION31 cn (NO 3ZIS m LU 3dld w L) CL - EL 3dOIS (S=10) o NOIS30 J, z z w LU 13381S LU < ' W Z < LLI LLJ 0 >- C3 uj EldOls Cl D w 0 C,: (Sjo) D o R§()Z 00 2'' 0 (ov) U LL, 7 Of 0 0 z M (vo) :K Z F- LLI F- Ct U) -i z < (D (HH/Nl) I W Z — m 0 Lu it 0 (N I IN) 31 U 0 F- U) Lo 'o w ma) o P-: (P q C) 0 (?J0 1 �o cq 'o cq cq 'oH/N cli N (Mvy) 31 Lo Lo Lo z Z) (ov) vo cli. 'o 'o ll� C) C) 0 LLI JJONnH 6a) 0) ci a3 ci (ov) co C14 ll� U) V38V cD CD 0 LL 0 U- 0 N0163C] < w VM:IV w INIOd LU 0 z NEAS30 C14 m C14 L Lu * L) 0 w U) F- CO LU 0 LU ul LU z z LU -i w < cn I , cq co IT co w 0 '0 Al LU (NIW) U < < LU -i (Schg) A k HION91 (NO 3ZIS CO Lu Eldid w LU CL E 229 NOIS30 (Sjo) D z Lu 13MJIS z Lu M 0 w cc C— < W z < LU LLI +®« LU D 0 CD (S-qo) D ip to Z o >- 0) no 2'* t (OV) U QLLJ �= =0m z NO) 3 Z < <Lu Z < WHINO I w Q Z Fn m 0Lu (N I VW Ol u 0 U) 00 '0 § OR C) N ®H/Nl) I CR CR § (N IVY) 01 tO 0 z :3 (OV) vo ". 7 C) C) a u LU LO a) 6 LO a) 6 m 0) 6 =IJONnH (OV) 00 0) 00 V3UV o C) 0 0U. LL 0 F- N01630 w V38V w iNlOd C14 CY) F- co CN w a NOIS30 w Q L) a Lli 0 LU U) LU U) LLJ LU z zw < m to k _ \ w \ \\ Wa&\ LU \ /cG>6» § c,\ \ ) Emz WO A2 > a \ CO/ a2 2 m $ IL \ e e@s / mgo\ wOIS « \ m±o\ z -z_ waa2LU \)\ loll \� �\/ a m3o J§\)§ �, o 0m R z <Lu ¥§/mac &4o0 we C�{§` ==e0 w&t §[{ ®� © \ ) § r r . �w&t zc ,q \ �a/a \ ® c, m / as o G J %§ ,eee < _ § s» ® mG r / / @e . } ( ) \ / § E » i < W M O W V' O rn rn M o F- tO N W Z n N Z 0) N IT r 0 W F 00 Cl) co O N Y ¢ 00 W >Or` W S Z — v v U < y U M > n o i < 0 LO o W o WW (n a. N O J co O -ITZ U Cl)O o 0-' O co(/1 O W W .... 0) F r J Z Z ¢ O O F N o OD 0 0 W W v O O N� U m Z w LL U � W —t v ado c Z y O V W o 0 0 E O Z QWN Z� E r vi o0 2 ¢F-- d U) O J OD o O O O Q d O wLO ¢ U °O W y O Jj O O Q U Z p'< O O � W U- LL IL O O J F O W d W F- w rn ° w LU a F- X w Cl) a D w w xt f- U z - O a U W 0 V% O J a ALLEY - JEFFERSON CHASE DRAIN Worksheet for Rectangular Channel Project Description Worksheet CHASE DRAIN Flow Element Rectangular Cht Method Manning's Forme Solve For Discharge Input Data Mannings Coeffic 0.013 Slope 010000 ft/ft Depth 0.50 ft Bottom Width 2.00 it Results Discharge 5.50 cfs Flow Area 1.0 ft' Wetted Perimi 3.00 ft Top Width 2.00 ft Critical Depth 0.62 ft Critical Slope 0.005490 ft/ft Velocity 5.50 ft/s Velocity Head 0.47 ft Specific Enerc 0.97 ft Froude Numb, 1.37 Flow Type supercritical Project Engineer: Sean J. Welsch e:\270pin-1\data\270fio-1.fm2 Welsch Design Consultants Inc FlowMaster v6.0 [614e] 12/26/03 02:30:30 PM 0 Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA (203) 755-1666 Page Yof Project Description Worksheet Circular Channel Flow Element Circular Channel Method Manning's Formu Solve For Discharge Input Data Mannings Coeffic 0.010 Slope 010000 ft/ft Depth 0.50 ft Diameter 6 in Results Discharge 0.73 cfs X 3 Z,IG Lrs --4> /0/ AL G,4PAe rT `/ 0,1" 6" PVC PIPES IN CHASE DRAIN Worksheet for Circular Channel / H / S LA LG , /5 /-02 A JJ5 /N 6 c i'I-fr , il'+E OF5/GN /5 3 1--A2A GLi5L Flow Area 0.2 ft' Wetted Perime 1.57 ft Top Width 1.49e-8 ft Critical Depth 0.43 ft Percent Full 100.0 % Critical Slope 0.009288 ft/ft Velocity 3.71 ft/s Velocity Head 0.21 ft Specific Energ, 0.71 ft Froude Numbe 1.8e-4 Maximum Disc 0.78 cfs Discharge Full 0.73 cfs Slope Full 0.010000 fUft Flow Type 3ubcritical Project Engineer: Sean J. Welsch e:\270pin-1\data\270f10-1.fm2 Welsch Design Consultants Inc FlowMaster v6.0 [614ej 12/26/03 02:31 :36 PM © Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA (203) 755-1666 Page Yof }' 1; // PINE ST. - NW CURB - EX. 100-YR CONDITION Worksheet for Gutter Section Project Description Worksheet Gutter Section Type Gutter Section Solve For Spread Input Data Slope 010000 ft/ft Discharge 2.62 cfs Gutter Width 0.00 ft Gutter Cross Slol083300 ft/ft Road Cross Slop 014000 ft/ft Mannings Coeffic 0.013 Results Spread 11.96 ft Flow Area 1.0 ft' Depth 0.17 ft Gutter Depress 0.0 in Velocity 2.62 f /s Project Engineer: Sean J. Welsch e:\270pin-1\data\270f10-1.fm2 Welsch Design Consultants Inc FlowMaster v6.0 [614ej 12/26/03 02:34:43 PM © Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA (203) 755-1666 Page A of A' 7 It CITY OF FORT COLLINS .SjorI►ttwaler Bavinx 0Dry Greek Basin .. h. '. fuJMi • sr erarnbi tz.Eveo €fir ecr. 9 a si n 01d Town No4h B �n ` WVV,neVineasin Id Town B .1rs+; ! 7 -5 u Clatfcin sas, V..4• ie M. a i �. Spring Cre:c'k Basin {}-' Fossil Ctotk B;tsr► rt . .r J Foothills Basi r Nle;Cldlands Mail Crock B: m 0 a fS� z 1? EYWEOR L n 1141mr.=7 Legend Parcels UUCANGIMUSI sIr331 .r.3ntw%nN s t '.:II-K •tVa Fgbo'aN-um]u's dcaaaa p 9 N marr jv y'1 ■. �Ci.-l.y I aasa' Ldke5 and VNaleraif l� dl35y [y�4CUNAY[Q Clly Limits '.YNWNTAN AYL LNWN7AW AVC ` r WO a 1 c ( 1 a LUAKSTx� 7L KSI czi 0 S A L i`fpeYre fif ` r I LOUVEST ' r M M araled �aY AwlMi-Cs►rriYnl {LJ1BBFill713NInc_ _ ®O http://gisims2. fcgov.com/servlet/com.esri.esrimap.Esrimap?ServiceName=overview&Client... 7/l /2003 !/ A 050 l .j i 1 `fl T 71l 7;•�.. t r wv.�.a.i�naRlus-c.vrr�aatarabo. ri � _•w_• _ill _...t Legend Parcels RaiTxjs }6 Slreel Cenlerines ^i Pradacl ✓arrido, - FEM4 Fbodp bins - � vtN •t gil �a r•)J Acr ■ =1A41g�9 na 'owtns: -l1A Vaa:or 4>. N1 Yco Aerial Phalo City Urnil- http://gisims2.fcgov.com/servlet/com.esri.esrimap.Esrimap?ServiceName=overview&Client... 7/l /2003