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Home My WebLink AboutLARIMER COUNTY COURTHOUSE OFFICES - SITE PLAN ADVISORY REVIEW - 37-98C - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTNJCXTE Preliminary Drainage & B E Y O N D E N G I N E E R I N G Erosion Control Study Larimer County Administration Building REFERENCES. 1. Storm Drainage Design Criteria and Construction Standards (FC-SDDCCM), City of Fort Collins, Colorado (Revised January 1997). ._ 2. Drainage Criteria Manual (Manuao, Urban Drainage and Flood Control District, Wright - McLaughlin Engineers, Denver, Colorado, March 1969. 3. Old Town Basin Master Drainage Plan, City of Fort Collins, Colorado, prepared by Resource Consultants & Engineers, Inc., January 1993. 4. Old Town Basin Master Drainage Plan Update, City of Fort Collins, Colorado, prepared by Anderson Consulting Engineers, Inc., February 2001. (Draft Report) 9 NAROI74\Drainage\Word\Fc0174_DrainageReport.doc • 9 E Y O N D E N G I N E E N I N G 6.0 CONCLUSIONS Preliminary Drainage & Erosion: Control Study Larimer County Administration Building 6.1 Drainage Concept The proposed drainage concepts presented in this study and shown on the final drainage plans adequately provide for the conveyance of developed runoff from the proposed development. 8 N:\Fc0174\Drainage\Word\Fc0174_DrainageReport.doc NOXTE Preliminary Drainage & Erosion Control Study 6 E Y O N O E N L I N E E N i N G Larimer County Administration Building 5.0 EROSION CONTROL 5.1 General Concept The Larimer County Administration Building is in the Moderate Rainfall and Moderate Wind Erodibility zones per City of Fort Collins zone maps. Until the disturbed ground is vegetated, the potential exists for erosion problems during and after construction. In accordance with the City of Fort Collins Erosion Control Reference Manual for construction sites, the erosion control performance standard shall be 96.0% during construction and 99.0% after construction. 5.2 Specific Detail The Site is situated such that, during construction, disturbed areas drain overland and to the existing curb and gutter systems. Therefore, erosion control measures such as silt fencing and inlet protection will be necessary. These areas may or may not require regular maintenance depending on the conditions during the construction phase of development. Following completion of the overlot grading all areas that will not be paved shall be mulched and seeded. G 7 N:\Fc0174\Drainage\Word\Fc0174_DrainageReport.doc rNkOL)= Preliminary Drainage & Erosion Control Study BEY ON D E N G IN E E R ING Larimer County Administration Building Developed runoff in basin 204 (0.48 ac) travels overland through landscaped areas and the eastern part of the south parking lot on the south side of the building. The flows are routed by curb and gutter to the east and -then to the north to D.P. 204. A 5' Type `R' inlet captures the water and routes the water to the on -site storm drain system. The roof area for the Administration Building is delineated as Basin 300 (0.79 ac). Rainfall is captured by roof drains and carried by an internal storm drain system. This system releases the water into the on -site pipe system at SD-MH2 and SD- MH3. 6 NAFc0174\Drainage\Word\Fc0174_DrainageReport.doc NO= Preliminary Drainage & Erosion Control Study B E Y O N D E N G I N E E R I N G Larimer County Administration Building Basin 103 is located on the east side of the Site along Mason Street. The developed runoff in Basin 103 (0.56 ac) traverses landscaped areas and the half street, which enters existing curb and gutter that routes flows north to D.P. 103. This storm water will be captured by a 10' Type `R' inlet designed by RMC for the proposed Oak Street Outfall project. Developed runoff in basin 200 (0.63 ac) flows overland through the south parking lot. The flows are caught by curb and gutter that route the storm water to the southeast comer of the basin, D.P. 200. A 5' Type `R' inlet captures the water and routes the water to the on -site storm drain system. Developed runoff in basin 201 (0.66 ac) flows overland through the west parking lot. The flows are caught by curb and gutter that route the flow to the northwest comer of the basin, D.P. 201. A 5' Type `R' inlet captures the water and routes the water to the on -site storm drain system. Developed runoff in basin 202 (0.20 ac) flows overland through the northernmost part of the west parking lot. The flows are caught by curb and gutter that route the flow west to D.P. 201. A 5' Type `R' inlet captures the water and routes the water to the on -site storm drain system. Developed runoff in basin 203 (0.11 ac) flows overland through the loading dock area on the east side of the building. A trench -drain that routes the flow west to D.P. 201 catches the developed flows. This drain outlets into the proposed on - site storm drain system. 5 N:\Fc0174\Drainage\Word\Fc0174_DrainageReport.doc NOLTE Preliminary Drainage & BEY ON D E N G IN E E R ING Erosion Control Study Larimer County Administration Building 4.0 DEVELOPED DRAINAGE CONDITIONS 4.1 General Concept The proposed Larimer County Administration Building has a minimal effect to the area of imperviousness throughout the Site. Including all the proposed on -site drainage basins, the Site has a 76% imperviousness while the current Site consists of 77% impervious area. In general, developed runoff from the proposed Site improvements will sheet flow across parking areas to curb inlets at various locations. Roof drainage will enter a storm drain system that routes water from the inlets to the proposed Oak Street Outfall. Developed runoff along the Site's West side of the building will sheet flow across landscaped areas to a curb and gutter system that leads to inlets that are proposed as part of the off -site storm system. There is no detention requirement currently associated with this Site. The developed runoff from this Site will enter the proposed off -site storm drain system and ultimately enter the Poudre River. 4.2 Basin Descriptions Basins 100 through 103 contain areas adjacent to the Site and contain half street areas as well as landscaped and sidewalk areas. Developed runoff in Basin 100 (0.57 ac) flows overland through sidewalk and landscaped areas to curb and gutter P to D.P. 100, which is situated at the basin's eastern end. Basin 102 envelopes the northern one-third of the Site from the building face to the midpoint of Mountain Avenue. The developed runoff in Basin 102 (1.47 ac) sheet flows across landscaped areas and enters existing curb and gutter that routes r' the runoff east to D.P. 102. Multiple grate inlets will be designed to accept this I flow that enters the off -site drainage system through a 30" RCP. The grated inlets are being designed by RMC as a part of the proposed Oak Street Outfall project. 4 NAFc0174\Draina¢a\word\Fc0174_DrainaeeReport.doc ITable 2.4 Summary of Peak Discharges for Fully Developed Conditions with Existing Drainage Facilities in the Old Town Basin and Master Plan Drainage Facilities in the Canal Importation Basin. SWMM ID Location Peak Discharge (cfs) 2-Year 1 5-Year 10-Year l 25-Year 50-Year I00-Yea CSU Model 230 Elizabeth Street at Shields Street 138 11 209 272 . 367 476 614 206 Laurel Street, West of Washington Street 13 21 28 40 55 77 209 Laurel Street, West of Loomis Street 10 17 22 29 36 47 392 College Avenue at Locust Street 35 44 51 81 105 130 Old Town North Model (With Howes Street Outfall) 733 Mulberry Street, West of Loomis Street 40 70 97 144 201 284 419 Mulberry Street, West of Meldrum Street 47 74 98 138 185 250 413 Myrtle Street at Meldrum Street '41 65 . 85 123 172 250 450 Canyon Avenue, North of Olive Street 0 0 0 i 0 0 4 449 Magnolia Street, East of Canyon Avenue 1 33 123 300 518 826 690 Pond 605 Release to Mason Street, North of Olive Street 2 6 27 82 168 287 692 Pond 605 Release to College Ave, North of Magnolia St 22 41 104 211 318 443 693 Pond 605 Release to College/Mulberry Pond (#604) 0 0 7 34 106 226 686 Pond 604 Release to College Ave, North of Magnolia'St 1 1 2 3 5 1 11 685 Pond 604 Release to Magnolia/Remington Intersection 2 3 5 9 15 32 682 Pond 604 Release to Myrtle/Remington Intersection 42 73 102 169 249 374 638 Peterson Street at Locust Street 0 4 8 14 24 .60 812 Plum Street at Whedbee Street 37 52 67 93 132 169 727 Myrtle Street at Riverside Avenue (street flow) 63 119 180 332 514 8 927 Myrtle Street at Riverside Avenue (storm sewer flow) 61 79 95 106 110 111 724 Mulberry Street at Riverside Avenue 41 71 98 159 231 318 851 College Avenue, South of Olive Street 22 41 104 211 320 450 852 College Avenue, North of Olive Street 21 36 80 I 145 208 283 860 College Avenue, South of Oak Street 22 39 81 147 212 288 861 College Avenue, North of Oak Street 18 31 61 102 139 181 577 Mountain Avenue at Shields Street 79 123 163 246 354 515 435 Mountain Avenue at Loomis Street 11 37 75 151 245 380 442 Mountain Avenue, West of Howes Street 25 35 43 55 70 90 445 Mountain Avenue at Mason Street 76 115 147 194 251 349 543 Mountain Avenue at College Avenue 90 141 182 247 347 537 962 Mountain Avenue at Mathews Street 121 188 245 336 455 1 694 422 Mountain Avenue at Peterson Street 68 1 132 187 .277 405 644 460 Laporte Avenue, West of Shields Street 30 47 61 88 123 172 464 Laporte Avenue at Loomis Street 44 71 96 136 187 255 631 Laporte Avenue at Howes Street (street flow) 68 124 175 286 456 700 633 Laporte Avenue at Howes Street (storm sewer flow) 113 127 127 127 127 127 447 Maple Street, West of the Howes Street Outfall 7 10 12 16 21 30 458 Howes Street Outfall, North of Maple Street 64 119 173 288 458 705 459 Howes Street Outfall, North of Cherry Street 196 299 387 537 735 1038 508 Cherry Street at Wood Street 18 28 37 53 74 103 473 Cherry Street West of Whitcomb Street 33 50 67 100 140 195 474 Cherry Street at Meldrum Street 36 59 81 119 166 226 548 Cherry Street at the Howes Street Outfall 39 65 91 136 187 260 Old Town North Model (With Howes Street Outfall and Locust Street Outfall) 967 Mvrtle Street at Riverside Avenue 1 34 93 1 156 i- 298 503 798 7:\0PEN\Cofc14\cof64 tbl24.wpd ANdERSON CONSUI]iNG ENGINEERS, INC. j 3 S DRAFT REPORT OLD TOWN BASIN MASTER DRAINAGE PLAN UPDATE (Partial Baseline Analyses) PREPARED FOR: City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80521 PREPARED BY. Anderson Consulting Engineers, Inc. 2900 South College Avenue, Suite 3B Fort Collins, CO 80525 (ACE Project No. COFC14) February 16, 2001 ANdERSON CONSU1TINq ENGINEERS, INC Civil • YTIater Resources 0 Environmental " - '/ ,, I. r A I M. IV. \r LU I 1 4 �.UU \LIIII \ -ERVI'-: PROJE--, DRAVANG NAME: FC0174-SWMMMA':4 EXCERPTED FROM: CITY OF FORT COLLINS OLD TOWN BASIN MASTERPLA UPDATE,ANDERSON CONSULTING ENGINEERS, INC. (02/16/01) 3 488 U @4 1- 4- > V, 9 it 3 054,3 6 R41. 3 "3 4 V 3 .6 40 FF22 7 i5 23,4 >1 ec ....... OAK ST 3 55 n: 1 4 V W wit -'ni 1Ii { 1. i+rA� `� i ia. r 4 U "N I I W 5 4.5 W' 1g, rl"� Em 5 0 . ............... . . ......... *V A if 4 --7' N.T.S.I Al E Y 0 N D E N 0 1 N E E R I N 0 sot N" P001T DANE KM A. FORT COU.Nk 00. 0525 6702WILM TEL 9702n2415 FAX MAOLTE-COM f 34 LARIMER COUNTY ADMINISTRATION BUILDING SHEET NUMBER Old Town Basin Subbasin and Conveyance Map EXHIBIT 3. OF 1 SHEETS PREPARED FOR: LARIMER COUNTY DATE SUBMITTED: 10/26/01 JOB NUMBER FC0174 I 4•L. i4-. i.rr4 JAIL. J/[J/U. eA IT. rv:\r CV I I C000\uvII� �E°'JER: fC5' SERVICE: PROJECT DRAWING NAME: =»174_SWMMMAP.GWG EXCERPTED FROM: CITY OF FORT COLLINS OLD TOWN BASIN MASTERPLAN UPDATE, ANDERSON CONSULTING ENGINEERS, INC. (01/29/01) a EPTHI fm a Jt i. 1- �k7fIC .i.w4. ri4 ..L • . � 'ARM1.O9yea FL 1"`�F�`JY��W�v711��f�� #3��1'��8`L�: �-'�.A�fFr,"s./3'.�i��"`•S�$�a�4►O� •sa >- �'eyp '� ;' - ♦ i `TiLi 1!v rl � �t1E'T F �k^� li ♦f� t �.'f �'��'i� ♦ '�� ♦♦� � ♦ ♦ `�'''i� I '� ,, sr,'.,' gin. L 1 LARIMER COUNTY ADMINISTRATION BUILDING SHHET NUMBER NJ(:XTE 11 • Town ■ • • • • • EXHIBIT• •: PREPARED FOR: • DATE SUBMITTED: Ili NCCTE Preliminary Drainage & Erosion Control Study BEYOND ENGINEERING Larimer County Administration Building 3.0 HISTORIC DRAINAGE BASINS 3.1 Major Basin Description The existing Administration Building lies within the Old Town Master Drainage Basin. This basin is located in the central part of Fort Collins. Historically this basin has traveled through streets to the Poudre River during major events. There are currently small storm drain systems in place to capture nuisance flows and route them to the Poudre River. Resource Consultants & Engineers, Inc. prepared the Old Town Master Drainage Plan, in January 1993. This report outlines the floodplain associated with the Poudre River and Larimer #2 Canal. There is currently a Draft Report for the Old Town Master Drainage Plan Update (Partial Baseline Analyses) prepared by Anderson Consulting Engineers, Inc. that delineates the flood plain that incorporates the current urban development in the area. Referencing this report dated February 16, 2001; the Site does not lie within the flood plain. Exhibit 2 reflects the flood plain boundary in relation to this Site. Exhibit 3 is the sub -basin and conveyance map for the area and shows the runoff routing. This information relates to Table 2.4. Rocky Mountain Consultants, Inc. (RMQ are designing the Oak Street Outfall, a large storm drain system, which is going to route the Old Town Drainage Basin storm water to the Poudre River. These improvements are referred to in this report as the Off -site improvements. A 48" storm pipe is designed along Mason Street and runs south to Oak Street. From this point, storm water enters a 78" storm pipe that conveys it to the east. Inlets have been designed at the intersection of Mason Street and Mountain Avenue as well as Mason Street and Oak Street. 3 N:\Fc0174\Drainage\Word\Fc0I 74_DrainageReport.doc NOLTE Preliminart, Drainage & Erosion Control Study B E VON D E N G IN E E B ING Larimer County Administration Building 2.0 METHODOLOGY 2.1 Compliance with Standards The final drainage report that follows was prepared in accordance with the requirements and procedures for storm drainage design set forth in the City of Fort Collins Storm -Drainage Design Criteria and Construction Manual (i.e., FC- SDDCCM) and the Urban Storm Drainage Criteria Manual (i.e., Manuao. 2.2 Analytical Methods The Rational Method was used to analyze the respective design storm (i.e., 2-year and 100-year) runoff (Refer to Appendix A). This method is widely accepted for drainage design involving small drainage areas (<160 acres) and short times of concentration. It is ideal for storm sewer sizing and simple detention pond sizing or design situations where only the peak flow rate and/or the total volume of runoff are needed. The Rational Method relates peak discharge to the runoff coefficient, rainfall intensity, and drainage area. The rainfall intensity and runoff coefficients were taken from the FC-SDDCCM In addition to the methods mentioned above, this preliminary drainage study was prepared using several software packages, including the following Haestad Methods software: StormCAD and FlowMaster; and Urban Storm Drainage Criteria Manual software: UD Inlet and Gutter Conveyance. 2 NAFc0174\Drainage\Word\Fc0174_DrainageRepomdoc i;. :.m. unit: w/"/„ - tin: rv: \rcuir+\cKuu \nvn\ SE' iER: F-5' SERVICE: PROJECT -?AVANG NAME: FC0174_VICMAP.DC Le-:e-P y�all P * flity 1 ufal ibr ur Sri T S. • ncion In 71 r 3 _ gg .: _._._...Y3 NOL� LARIMER COUNTY ADMINISTRATION BUILDING SHEET NUMBER VICINITY MAP 1 BEYOND ENGINEERING EXHIBIT 1. OF 1 SHEETS w NLMP PONE ORE Km A FORT COLUq CO. W525 JOB NUMBER 070=4W Ta 0702W415 FAX W"MTECOy PREPARED FOR: LARIMER COUNTY DATE SUBMITTED: 10/28/01 FC0174 rqC& ` Preliminary Drainage & e E Y'O N D E N G I N E E R I N G Erosion Control Study Larimer County Administration Building 1.0 INTRODUCTION 1.1 Site Location The proposed Larimer County Administration Building (Site) is located near Old Town Fort Collins at 200 West Oak Street. The Site is bordered by Mountain Avenue on the North, Mason Street on the East, Oak Street to the South, and 'Howes Street to the West (See Vicinity Map). More particularly, the Site (3.67i acres) is located in Section 11, Township 7 North, Range 69 West of the 6`h Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. 1.2 Existing Site Description In general, the northern portion of the Site, slopes north and east along grades that are, on average, very flat. There are currently 3 buildings that occupy the Site. The two buildings to the south and west of site are multiple level brick buildings encompassing 34,239 ftZ (0.78 acres). There is also a 24'x56' pre -manufactured building on the north side of the Site. The center of the Site consists mostly of asphalt parking and sidewalks. There is a pedestrian -way around the entire block with a 10' to 14' tree -lawn. There is no on -site detention and the Site sheet flows all storm water to the surrounding streets. The terrain, in its existing state, is approximately 76% impervious. 1.3 Proposed Project Description The Larimer County Administration Building will be one five -story, predominantly brick building. The proposed building is 34,418 ftZ (0.79 acres) and the parking area will have 128 parking spaces and 6 handicap spaces. The parking is located on the south and west sides of the building. The north one-third portion of the Site will be heavily landscaped with a meandering pedestrian walkway. A truck docking area has been designed for the east side of the building. Vehicle access for the Site will be from Howes Street and Mason Street. 1 N:\Fc0174\Drainage\Word\Fc0174_DrainageRepon.doc NO' Preliminary Drainage & BEYOND ENGINEERING Erosion Control Study ' 'Larimer County Administration Building TABLE OF CONTENTS PAGE 1.0. INTRODUCTION............................................................................................................. l 1.1 Site Location.........................................................................................................1 1.2 Existing Site Description......................................................................................1 1.3 Proposed Project Description...............:....`::.:................:...:...................:::...:........1 . . 2.0 METHODOLOGY............................................................................................................2 2.1 Compliance with Standards..................................................................................2 2.2 Analytical Methods...............................................................................................2 3.0 HISTORIC DRAINAGE CONDITIONS.........................................................................3 3.1 Major Basin Description.......................................................................................3 4.0 DEVELOPED DRAINAGE CONDITIONS....................................................................4 4.1 General Concept....................................................................................................4 4.2 Basin Descriptions................................................................................................4 5.0 EROSION CONTROL.....................................................................................................7 5.1 General Concept.....:.........................................................................................7 5.2 Specific Detail.......................................................................................................7 6.0 CONCLUSIONS...............................................................................................................8 6.1 Drainage Concept..................................................................................................8 REFERENCES.................................................................................................................9 APPENDIX A - Developed Site Hydrology • Developed Runoff Calculations • .Hydraulic Calculations APPENDIX B - Erosion Control Calculations APPENDIX C - Charts, Tables & Graphs BACK POCKET - Drainage and Erosion Control Plan (Sheet C8) 1 - N:\Fc0174\Drainage\Word\Fc0174_DrainageReport.doc LARIMER COUNTY ADMINSTRATION BUILDING PRELIMINARY DRAINAGE & EROSION CONTROL STUDY for ................... ................... 21:1"lil1er Cioun. . ............... .. 2555 Midpoint Drive, Suite D Fort Collins, Colorado 80525 Nolte Associates, Inc. 1901 Sharp Point Drive, Suite A Fort Collins, Colorado 80525 (970) 221-2406 October 29, 2001 LARIMER COUNTY ADMINSTRATION BUILDING PRELIMINARY DRAINAGE & EROSION CONTROL STUDY 1st Submittal BE YON D E N G IN E E R ING