Loading...
The URL can be used to link to this page
Your browser does not support the video tag.
Home
My WebLink
About
OLD TOWN NORTH - 50% PDP - 28-99A - SUBMITTAL DOCUMENTS - ROUND 3 - DRAINAGE REPORT
Job No. 1646-01-98 Shear Engineering Corporation Designer: meo Old Town North 12/1/2000 8:02 AM Detention Volume Required Foi 100 -Yr Storm for Cumulative Runoff Method for Sizing Detention Ponds Release Rate = 0.38 c s acre from hydrologic model update by L & A Land use Assumptions SFH Roa s Open MFH 100% 0.69 - C2 % % % % C2 Percentage C2*Percentage 0.65 0.95 0.20 0.70 40% 25% 10% 25% 0.26 0.24 0.02 0.18 Design Storm Release Rate 100 year cfs Runoff Coetticient Area 0.87 - CI00 acres 14.29 37.61 [Initial Time 5.00 minutes Time Increment 5.00 minutes Contributing Areas West 5.88 ac East 31.73 ac Total 37.61 ac Inflow vs. Outflow 500000 450000 400000 C, 350000 U 3 300000 0 LL `0 250000 L E 200000 O 150000 100000 50000 0 h 5 by �y t°b yc, ob 1y %1D qb Time (min) —�— Release Volume (cO --F Inflow Volume (co POND CUHP.xls Prelim Cuhp Page 1 of 5 14 Table 3.1. Summary of Results of the Developed Condition Hydrologic Analysis Node Description DrainageI. Peak Discharge (cfs) 2-Yr 5-Yr 10-Yr: 50-Yr ..:.I. 100-Yr. Area (ac) 615 Total Flow at the Poudre River 3,107 710 1,440 2,000 3,590 4,410 614 At the Poudre River (Existing Channel) 620 390 720 930 1,530 1,810 612 Mulberry Street (Existing Channel) 599 380 710 920 1,500 1,770 611 At the Poudre River (Proposed Channel) 2,488 450 980 1,370 2,470 3,040 610 Mulberry Street (Proposed Channel) 2,469 460 980 1,380 2,490 3,060 603 Vine Drive 1,882 460 980 1,340 2,400 2,920 602 Lemay Avenue 790 240 460 600 990 1,180 600 College Avenue 155 160 290 380 590 700 Results of the developed condition analysis along the proposed channel alignment (and the existing channel upstream of the airport) are graphically presented in Figure 3.1. This figure shows the 100-year hydrographs at major road crossings along the main channel. The attenuation which was noted between Vine Drive and Mulberry Street in the existing condition analysis is no longer present due to both the developed nature of the local watershed and the substantially more efficient conveyance system. Figure 3.2 shows the 100-year hydrographs along the existing channel. downstream of the airport. A summary output file for the 100-year developed condition event, which includes a printout of the main channel hydrographs at all major road crossings, is contained in Appendix C. Full output for each of the return period events, which includes hydrograph listings for all subbasins and conveyance elements, is provided on the enclosed diskettes. Table 3.2 provides a comparison of 100-year discharges for the revised Master Plan (current) model and original Master Plan model [3]. The table indicates significant differences between the two models. This is primarily due to two factors: (a) the original Master Plan assumed that approximately 2,900 cfs would be conveyed from the Upper Basin to the Lower Basin during the 100-year event, while the current model assumes that all runoff from the Upper 18 Job No. 1646-01-98 Shear Engineering Corporation Designer: meo Old Town North INPUT FOR OUTLET STRUCTURE DETERMINE ORIFICE SIZE Design Release Required Q= CA(2gH)A0.5 Storm Rate WSEL A = Q/(C(2gH)A0.5 yr cfs ft H (ft) = 3.88 100 14.29 61.88 C = 0.65 Q (cfs)= 14.29 A (sf) = 1.39 R (ft) = 0.666 D (ft) = 1.331 Use 1.39 ft diameter orifice = 16.68 inches LOWER ORIFICE DIAM. (ft) LOWER ORIFICE INV. (ft) LOWER ORIFICE COEF. (Cl) UPPER ORIFICE DIAM.(ft) UPPER ORIFICE INV. (ft) UPPER ORIFICE COEF. (Cu) Pipe Diameter (ft) PIPE SLOPE (ft/ft) MANNINGS n 1.39 WEIR LENGTH (ft) 0.00 58.00 WEIR INVERT (ft) 0.00 0.65 WEIR COEF. (Cw) 0.00 0.00 TOP OF BERM (ft) 62.00 0.00 INIT. DELTA (ft) 1.00 0.00 DELTA HEAD (ft) 1.00 OVER FLOW yes 2.50 WEIR LENGTH (ft) 200.00 0.0040 WEIR INVERT (ft) 61.90 0.012 WEIR COEF. (Cwo) 2.60 *OUTPUT* Pipe Area (sf) 4.91 P 7.85 ft HYD. RAD (FT) = 0.625 ft R"2/3 = 0.7309 Outlet Pipe Capacity = 28.10 cfs LOWER ORIFICE AREA (A) = 1.5175 sf UPPER ORIFICE AREA (A) = 0.0000 sf )RIFICE EQtN: CA(2gH)"1/2 TEIR FLOW EQTN. CwLH-3/2 TOTE: HEAD OVER ORIFICE = HEAD OVER CENTER OF ORIFICE POND CUHP.xls Outlet Page 4 of 5 12/1/2000 8:02 AM APPENDIX II Stuffer Envelope Conceptual Drainage and Erosion Control Plan (I Sheet) Table D.2. Subbasins for Which On -Site Detention is Required, and Their Allowable Release Rates. )eveloped::Gondtuon Subbasin ID On -Site Detention Facility ID:.:. Allowable Release Rate (cfs) 2-year Event ;: 5-Year. Event ' 10=Yeaz Event 4012 872 33.7 34.7 35.6 4063 850 273.6 277.1 280.4 408 851 3.1 5.3 7.3 410 852 7.4 12.7 17.5 416 853 21.2 34.7 45.7 417 854 12.4 20.2 26.6 419 855 31.7 51.4 67.0 420 856 16.6 30.6 43.8 421 857 13.8 23.2 31.2 422 858 22.1 35.8 46.8 423 859 24.5 39.8 51.6 425 860 19.7 32.1 42.1 426 861 1.2 2.2 3.1 4282 862 84.6 87.6 90.2 4293 863 38.8 41.0 43.2 432 864 3.7 6.4 8.9 4332 865 61.6 63.8 65.8 A 2A2 RCIA 399.5 403.0 405.8 437 867 6.9 11.3 14.7 438 868 6.2 10.1 13.2 440 869 28.4 46.0 60.0 446 870 4.0 6.6 8.8 447 871 5.2 8.6 11.5 454 873 30.5 49.6 64.2 456 874 8.1 14.4 20.1 ' Includes the 100-year runoff for the developed portion of the subbasin. U:\LA-ASSOCTLP-CITYNCOFC9606.TD2 As a result of this decision, all new development within the Lower Dry Creek Basin would be required to provide detention such that in the developed condition, runoff during the 100-year 1 event would be reduced to the 10-year historical release rate for the site. Table 4.2 is provided as a summary of subbasins for which on -site detention would be required and the allowable unit runoff rate associated with the 10-year historical runoff for each of these subbasins. The basin's response to developed conditions with the selected on -site detention alternative is shown in Figures 4.1 and 4.2. Results of the developed condition with 10-year detention analysis along the proposed channel alignment (and the existing channel upstream of the airport) are graphically presented in Figure 4.1. Figure 4.2 shows the 100-year hydrographs along the existing channel downstream of the airport. Full output for each of the return period events, which includes hydrograph listings for all subbasins and conveyance elements, is provided on the enclosed diskettes. ( ;u t o , w o,tw, , t 26 Table 4.1. Summary of 100-Year Peak Discharges for the Three On -Site Detention Alternatives. 100-Year Peak Discharge for the Node Description Drainage Area (ac) Given Detention Alternative (cfs) 2-Yr 5-Yr 10-Yr 615 Total Flow at the Poudre River 3,107 1,480 1,620 1,730 614 At the Poudre River 620 1,030 1,030 1,030 (Existing Channel) 612 Mulberry Street 599 980 980 980 (Existing Channel) 611 At the Poudre River 2,488 11000 1,120 1,220 (Proposed Channel) 610 Mulberry Street 2,469 1,010 1,130 1,230 (Proposed Channel) 603 Vine Drive 1,882 1,010 1,080 1,150 602 Lemay Avenue 79Q WO 850 860 870 600 College Avenue 155 560 570 570 The results presented in Table 4.1 indicate a relative insensitivity of the system to on -site detention for the range of alternatives analyzed. For the three on -site detention alternatives, the differences in 100-year discharges along the major flow paths are insignificant at many locations. Only at Mulberry Street and the Poudre River confluence along the proposed Dry Creek Channel do the 10-year detention discharges exceed the 2-year detention discharges by more than 20 percent. 4.3 Selection of the Preferred On -Site Detention Alternative Based on the results presented in the previous section, the Stormwater Utility selected the 10-year detention scenario as the preferred on -site detention alternative. Optimization of the basin's resources was the primary factor in making this selection. In choosing this alternative, it was noted that the incremental increases in discharges between the 2- and 10-year detention alternatives would not substantially affect the sizing of regional drainage facilities in the basin. At the same time, the 10-year detention scenario relieves on -site facilities of a significant burden, as compared to the 2-year detention alternative. c_ �7 Basin will be diverted to the Dry Creek Diversion Channel and does not enter the Lower Basin; and (b) the original Master Plan did not model the Lower Basin with the level of detail necessary to accurately estimate the magnitude of runoff potential associated with fully developed conditions. Table 3.2. Comparison of 100-Year Discharges for Developed Conditions as Reported in the Original Master Plan (31 and as Estimated by the Current Hydrologic Model. 100'=Year Developed C onditton 1�iscnarge (cts) I ocation„ LL Ongtnal Master Plan Revised Master Plan' Poudre River ConfluenceR27 4,410 Mulberry Street` 3,060 (1,770) Vine Drive 2,920 Lemay Avenue 1,180 College Avenue 700 Downstream of the 0 Larimer & Weld Canal ' Current hydrologic model b Combined discharge for the existing and proposed channels Discharge along proposed channel (discharge along existing channel) NR = Not reported 21 K 80 2400 rn 1800 r U 1200 600 0 _ Proposed Dry Creek at Poudre River Proposed Dry Creek at Mulberry Street — — Dry Creek at Vine Drive Dry Creek at Lemay Avenue 1 1 — Dry Creek at College Avenue 1 1 1 1 I 1 1 II 1 I 1 L- 1--- -- I---i----.i...-_..�_.-1=sue--- ----------------- : 0 1 2 3 4 5 6 7 8 9 Time (hours) Figure 3.1. Developed Condition 100-Year Hydrof hs along the Proposed Dry Creek Channel (Existing Dry creek Upstream of the Airport). 1200 ve14 800 600 ►. 6 w 400 200 - Proposed Dry Creek at Poudre River - ----• Proposed Dry Creek at Mulberry Street — ---- — — Dry Creek at Vine Drive --- Dry Creek at Lemay Avenue - ---- Dry Creek at College Avenue +--r-----�-� --I-- ---- �- -- I�- 1 2 3 4 5 6 7 8 g Time (hours) Figure 2.1. Existing Condition 100-Year Hydrographs along the Proposed Dry Creek Channel (Existing Dry Creek Upstream of the Airport). .b� � Z " i�:� jf�. �y •' ,a, :1ri.i 1' ,r�:S,, 1 ,. 1te ' irl_. .� � a �..� f ,' r.— ' �! t• 1° , . X"4l, - �s it �+r 7 Y ' r'yY I 1 x • Ito 1+ 1 j .: I �...,� f ��t±�i!•� r '�Co i�, y. }l sJ, - r y9�.9 I .�i. ' • � .t�,'�t �i 7 ^ • £ '��t � ( 1 i ♦ f .j il... 4 !&• w. r•. Y. � 71.a ! •.� a � ��� 1.• ..fii -! �t �I [[ �p �• 1�. LL 'llY1 . �' Y va ♦t5 5 Cr M� ; . � j „�' l� M : -f � ; '- r w �;,� t4`'•'+E ; f • � � +/,,,, ^ . 1.•l 1. A.--,�� � �•i. It � lr y �V, l it • i. cif f' ! - . • • t! rf 7 tic . / • �. ..1• �• �'f ( 'ly 5 •it ♦ � let � �) ® �! f' rt 'rI A •'i�r� y i�l lJ `tf • •d� t7i. u� . a(t ^^ii ,:• 1T:. !ty _ '� I p. ,S _-,�A r' • •fit !hy �, y• �1 � � •L+1 A-,1 Ii�N{,�l 6.7 LA ti��p ni�l1 t �`1 ♦r t �•, i'.�. r ' ♦. �. ,+♦. s tlY.1"wTl7Tw �4�T.•Gf1-.� .l +i •: ., 1r li�f� :. • � • �� �. 'jl• -iTS i '• '„•. of � ' �i n. �y r (�`S�•!, `�'� of `J• }J"aw. �,w. `i r♦ +.�,�-'7 ` r • • f � � � 4• �i .• t 1ST q . ,y 4:.' �•� ��.r ,� •1 �'.",lo �•1•rl l'��i �.. , . API I ••% `q�•;' Si(� •K\ 1 aV y ylrCiS !'1�;�'st tJ � ... :��}� � �r+'S4. r?• �•`hMc, Iy..S. �r I Y' ��., ILEI,! 1t. �u'- s r 9 r, ''Z •i � /A f • �.�ifaiafr,a''f(�1�1,,: '���. �I 1�, « •`� • r ;) "�7w7 w..,f �'[!� " • ' : ,� y ..�.,��t..r=JP_r,-♦' �{y. i�. =�Y•7��Jr �. •. 11�I�j t}'i.I ♦r Z_�yj� 'i.I�y Y,M^il:f``L.f N;5 ,'y IQIM{`.I',•y�. lr d �,+ 'l 1f_(. 1 /•. J•y 1,Y•':"lay ice•'i1. �^"_. t•1 r'!. �,l •�4•' ' ,.1 .I lot • • % �n yfA�1. y.Lvi �, ,''+ w� .t :it Ji.' ,�'; .vy 'ri.vP ~ 1,t�''iwju4•`"•i r'" "1 .� 1:!•+" ,r.^� F'. r �� 1� SJ•f•••� } � �, r, !1 - F'lP �f r 4 n. i � 1 � a �y�t� L~� •� y r F•r 1 fit{. ~ ,r .(r � : • �•• • , •t • � • S' to .,.. tJ..r �, a WW I \T, � •art „���j • T },���1c�.' '�j.��' .+ � ♦1 , t "ir1'�'I�y� ���� ..�r� � 1VJiSC.V.74'6? \� �Q' v 11'♦ 4�'f "t• 1 N r��•l=t+jTY�'f!`;tit• e` r r� {a •rn. ��1',_r� Ia9•�iki-�,.,(t',i�a�r{ f'���(1f�j��. {• .`1 ww j r. ��� ,, ly. `i a ��i }', a '' • L ♦ t{ '' •Yc)1,;� • u , . � •� �. L<S ' Lt y� I t 31k- ri•, '1,";'�. a:wl r "1 . � n . f , � � r,. _ �i •Ti.. t'tY•�.'�} ,{�y,1�a= 4 ,�( ��` �" ��� . ; tt i , * � � •�' i�'7.(, • �� �y .5 + �4 � ` � ,�91;•.': • i�',r.. � • ' • � 'y� a� y� i . _ M1 S� ��� -';k f �i;.. `� 1 +t / ♦ , ( • • ! ( (pKeaiKf1�11}•`•T µ' • r!.'' l' • .r3tltA 1� r ; �. `♦^ �� • •r 1�1�� y• a- +` M�.•Ci1r ,l rri ♦. �jl ..:�" ;t i �i�>��T�T ��r •+ i'' 'r4ti4iff:��1'� 7p��/j� � :� N �'r• i ay�c.c.lJ.}t D ��; xb ' ��,� ..'�.- ,^}y��,. � .v/i`�7�• (i ,�A.. .: 1� X'�f� �� t � .�"!� 1 � lt�!(�.f a� , i t '1 .. r r ;1 � �r'y '��'�• ,) � ,��'�,��. •�E�y . 4/ l;}. �j••i •�"•'t'l�f�'`0' 't .� ,�, ,• ii t����..I j, ,. ',� ]h'�'� w 4..1) r. •7 dt Z%VJ7t -�Yi[M ,. , ' i T'I�:i��J��,'Sf.'n.�jW.4'i•�in..i�� �'',f i+' %•' '"1.�.t t'• ,•'��'q� ,S�•. t�, 1r { yr. •.�,. v� ,vr•.r.rc.� r •r _; •.�%rh,M ;iJ°•�• �'i'Y/ q ♦ • • ��. �� Ly ;. `�' 1. r •1 • i-'A' • i!'. •:^i„,''ten I 7s Apt,• •.� •• • • eta t e ,:•. ,I .n i i C ,, r '�� ,f� � ,�i•¢, •.9 Sty. , W Job P� r, i -: `.'c•.. P a0 ` •. ] ° ` . i { \. •` I e i. a', till ��• � :�. e \ .. �e V \'• 35 so<, -•.._ iI •l ens"III 11\ F , rk • r 1 1 - EVE JGl 1 � NBRIAR �♦ 1, _ 1 Trai . .. - Parks =_ ':BASIN 497 l CA./AL tARI/d .R I •' _ I DRY, r(l/ RIVF N \ ER �• j `.� 77 , j I _ ``_ (�/'J1_ Ilummcr_�©lack Hollow �I � •- ..� v tir+ _ ' v:AmyS \/:••^'_- �♦: I % _ .Icy« Sqh: .lunCtin : 5�_ • �. I : _ — EASr�„ VINE' !" DRIVE k In Y.un._ BURL/NGTONND TNERN i.- � I rII y flr•r / 1 ,5etd,ns Idndcrsonvillc II �I JC_J�jll�r�"TrPa � III, qR I uckingf �(�, •� TT i/�I•/ 1. Imo— \�1.["11.. 1111`3' nh orl Ave l��` , a985 I .�i, p' : _ also+ „ ,r, t i', NNTOWN \ 1TVll Sc ` AJ 1 Parkll I'.' v9 7:♦ < I .... . (( / "S •. r FOQT! COLLINS �_ J�_� t t ,` ❑ �, �C`1, '•�; �\ i� IS `�. :i i III' ,(ti�j't AR ARA 'O Au— ir _ r_ El I ■ LJ 0 01� d'�� I 1d2r`.♦f�.`�c��• , —,I I Y���.rn—p—\�a.^I.', TII - _ o II j I / I \,�(\, y ` 1 1 I r ♦\ Ladcr C J 11❑J �II Tfail par.0 Pilk 3 _ �"� Arrhetd. „ F\uw. Figure 1.2. Vicinity Map for the Lower Dry Creek Basin I I. INTRODUCTION 1 1.1 General Dry Creek, located in north Fort Collins, Colorado, is a major tributary to the Cache la Poudre River. The creek's confluence with the river is located in the City of Fort Collins south of Mulberry Street and west of Summit View Drive. The watershed encompasses roughly 75 square miles, with about 62 square miles actually contributing runoff [1]. It is approximately 22.5 miles long and 5 miles wide, with the long axis having a north -south orientation. The northern terminus of the Dry Creek watershed is located approximately nine miles southeast of the Town of Virginia Dale, Colorado. The watershed is roughly bounded on the north by Bobcat Mountain and Boxelder Creek, on the west by a ridge which is located directly east of U.S. Highway 287, and on the east by Boxelder Creek and County Road 15. The elevation of the watershed ranges from 7,100 to 4,900 ft, msl. A location map of the entire Dry Creek drainage area is provided in Figure 1.1. For the purposes of this study, the City of Fort Collins has divided the Dry Creek watershed into two separate and distinct areas, an Upper and Lower Basin, with the dividing line being defined (except as described below) as the Larimer & Weld Canal. This canal transects the watershed in a roughly west -east direction approximately two miles north of Mulberry Street. The Lower Dry Creek Basin encompasses approximately 4.9 square miles. The distinction between the Upper and Lower Basins has been made in order to reflect the impact of the proposed Dry Creek Diversion Channel. As proposed by the City of Fort Collins, this channel would begin at the Larimer & Weld Canal and divert all of the upper basin flows (up to the 100-year event) to'. the Cache la Poudre River in an alignment to be located along the west side of the Union Pacific Railroad. Consequently, the diversion channel would serve to hydrologically separate the Upper and Lower Basins. The Lower Dry Creek Basin includes in its entirety, the Evergreen/Greenbriar Basin. The Evergreen/Greenbriar Basin is, in and of itself, a separate major drainage basin as defined by the City of Fort Collins. The Evergreen/Greenbriar Basin encompasses approximately 1.2 square miles and is bounded by College Avenue on the west, Dry Creek on the south, Lemay Avenue on the east, and (except for the Crestview Subbasin) Country Club Road on the north. Reference is made to the Evergreen/Greenbriar Master Plan for the definition of all subbasins and hydrologic modeling efforts associated with that basin [2]. The northern boundary of the Evergreen/ Greenbriar Basin defines the northern limit of the Lower Dry Creek Basin between College and Lemay Avenues. It is only in this area that the Lower Dry Creek Basin extends north of the Latimer & Weld Canal. A vicinity map of the Lower Dry Creek Basin is included in Figure 1.2. 1 N J FINAL REPORT HYDROLOGIC MODEL UPDATE FOR THE LOWER DRY CREEK BASIN MASTER DRAINAGE PLAN MOWN 6". IN 3-11X 1,A City of Fort Collins Stormwater Utility 235 Mathews Street Fort Collins, CO 80524 PREPARED BY: Lidstone & Anderson, Inc. 760 Whalers Way, Suite B200 Fort Collins, CO 80525 (LA Project No. COFC96.06) September 10, 1997 r r 4S,�pIly J. ,}Q_• O nnuuu�w APPENDIX II Portions of the Final Report Hydrological Model Update for the Lower Dry Creek Basin Master Drainage Plan; Prepared by Lidstone and Anderson; Dated September 10, 1997; Project No. COFC96.06 Job No. 1646-01-98 Shear Engineering Corporation Designer: meo Old Town North 12/1/2000 8:02 AM LOWER ORIFICE UPPER ORIFICE PRIMARY WEIR HEAD HEAD HEAD SUB ELEV. OVER LOWER OVER UPPER OVER WEIR TOTAL LOWER ORIFICE UPPER ORIFICE WEIR FLOW FLOW ORIFICE FLOW ORIFICE FLOW ft ft cfs ft cfs ft cfs cfs 58.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 59.00 0.31 4.37 0.00 0.00 0.00 0.00 4.37 60.00 1.31 9.04 0.00 0.00 0.00 0.00 9.04 61.00 2.31 12.02 0.00 0.00 0.00 0.00 12.02 62.00 3.31 14.39 0.00 0.00 0.00 0.00 14.39 61.95 1 3.26 14.29 0.00 0.00 0.00 0.00 14.29 OVERFLOW SPILLWAY HEAD ELEV. OVER WEIR Total WEIR FLOW Flow ft ft cfs cfs 58.00 0.00 0.00 0.00 59.00 0.00 0.00 4.37 60.00 0.00 0.00 9.04 61.00 0.00 0.00 12.02 62.00 0.10 16.44 30.83 Storm sewer From Irrigation Ditch Slope 0.0040 ft/ft From To Pipe Invert Slope Invert in out Length in out ft ft ft/ft ft Ditch MH 1 16.00 4552.90 0.0040 MH 1 MH 2 187.00 4553.16 0.0040 4552.96 MH 2 MH 3 373.50 4554.11 0.0040 4553.91 MH 3 MH 4 548.58 4555.81 0.0040 4555.61 MH 4 HW 32.34 0.0040 4558.00 Crnrm GPwpr Crossino with Existina Water and Sewer Lines Crossing is downstream from Proposed MH 2 Invert Dist to Ex. Pipe Storm Top of Ex. Pipe Ex. Pipe Top in crossing Invert Storm Inv Diam Ex. Pipe ft ft ft ft ft 4554.11 77.61 S/L 4554.42 4557.21 4549.53 1.25 4550.82 4554.11 95.86 W/L 4554.50 4557.29 4549.00 1.00 4550.04 Storm Crosses Sewer 105.61 DS from MH 11 Inv out MH 11 4549.73 ft Inv in MH12 4549.19 ft Dist between manholes 286.96 ft/ft Slope between manholes 0.0019 ft/ft Assume W/L same depth as S/L since it has to go under the ditch Ex. Pipes assumed to have 0.04 foot wall thickness POND CUHP.xls Outlet Page 5 of 5 Job No. 1646-01-98 Shear Engineering Corporation Designer: meo Old Town North Average End Area Method for determining Pond Volumes Invert 58.00 ft First Even Contour 59.00 ft Increment 1.00 ft Top Elevation 62.00 ft Stage E ev Area Volume Cum. Cum. Req' (A2) (V1) Volume Volume Volume ft ft sq ft cf cf ac-ft cf 0.00 58.00 0 0 0 0.00 328403 1.00 59.00 17120 8560 8560 0.20 328403 2.00 60.00 70172 43646 52206 1.20 328403 3.00 61.00 160798 115485 167 991 3.85 328403 4.00 62.00 205742 183270 350961 8.06 328403 Design Required Required Required Release Storm Volume Volume WSEL Rate year cf AF ft cfs 100 328403 7.54 61.88 14.29 Stage Storage 400000 350000 300000 250000 c+ E 200000 0 150000 100000 50000 0 58.00 59.00 60.00 61.00 62.00 Elevation (ft) -.- Volume Provided -0-Required Volume Elev East West Area Area 59.00 0 17120 60.00 0 70172 61.00 28896 131902 62.00 53119 152623 12/1/2000 8:02 AM POND CUHP.xls Stage Storage Page 3 of 5 Job No. 1646-01-98 Shear Engineering Corporation Designer: meo Old Town North 12/1/2000 8:02 AM Inflow Inflow Release Storage Storage Time Time Intensity Rate Volume Volume Volume Volume min sec iph cfs cf cf cf ac-ft 5 300 9.95 323.93 97180 4288 92893 2.13 10 600 7.72 251.33 150800 8575 142225 3.27 15 900 6.52 212.27 191040 128 33 178177 4.09 20 1200 5.60 182.31 218777 17150 201 227 4.63 25 1500 4.98 162.13 243194 21438 221757 5.09 30 1800 4.52 147.15 2648 77 25725 239152 5.49 35 2100 4.08 132.83 278941 30013 248928 5.71 40 2400 3.74 121.76 292224 343 00 257924 5.92 45 2700 3.46 112.64 304140 38588 265552 6.10 50 3000 3.23 105.16 315469 42875 272594 6.26 55 3300 3.03 98.65 325529 47163 278366 6.39 60 3600 2.86 93.11 335198 51450 283748 6.51 65 3900 2.72 88.55 345356 55738 289618 6.65 70 4200 2.59 84.32 354146 60026 294120 6.75 75 4500 2.48 80.74 363327 643 33 299014 6.86 80 4800 2.38 77.48 371922 68601 303321 6.96 85 5100 2.29 74.55 380223 72888 307335 7.06 90 5400 2.21 71.95 388525 77176 311349 7.15 95 5700 2.13 69.34 395264 81463 3138 11 7.20 100 6000 2.06 67.07 402394 85751 316 443 7.27 105 6300 2.00 65.11 410208 90038 320169 7.35 110 6600 1.94 63.16 416849 94326 322523 7.40 115 6900 1.89 61.53 424565 986 33 325951 7.48 120 7200 1.84 59.90 431304 1 229 11 328403 7.54 Detention Volume Required = 328403 c Detention Volume Required = 7.54 ac-ft POND CUHP.xls Prelim Cuhp Page 2 of 5 APPENDIX I Preliminary Drainage Calculations Page 11 Conceptual Drainage and Erosion Control Report Old Town North; Ft. Collins, Colorado IX. REFERENCES 1. City of Fort Collins "Storm Drainage Design Criteria and Construction Standards"; May 1984, revised May 1997 2. City of Fort Collins 'Erosion Control Reference Manual"; January 1991 3. Major Drainageway Planning Dry Creek; Prepared for City of Fort Collins, Larimer County and Colorado Water Conservation Board; Prepared by Gingery and Associates; Dated April 1980 4. Final Report - Hydrological Model Update for the Lower Dry Creek Basin Master Drainage Plan; Dated September 10, 1997; Prepared by Lidstone and Anderson, Inc; Project Number COFC96.06 5. FIRM map - Community Panel number 080102-0004-C; dated March 18, 1996. 6. Final Utility Plans prepared for Evergreen Park by VTN Colorado Inc; Plan approval Date by the City Engineer 03/27/74; VTN Project No: 172242. Page 10 Conceptual Drainage and Erosion Control Report Old Town North; Ft. Collins, Colorado VII. EROSION CONTROL: A. General Concept Erosion control measures will be specified on the Final Drainage and Erosion Control Plan. These measure will consist of the following; a. Silt fence along the property lines b. Gravel inlet filter at all storm sewer inlets c. Haybale barriers in all swales d. Wheel cleaning station at all construction entrances e. Haybale barriers around any inlets f. Buried riprap at all storm sewer outfalls g. Any other measure deemed appropriate at the. time of final design 2. Maintenance of erosion control devices will remain the responsibility of the contractor and the owner until the project is complete. VIII. CONCLUSIONS A. Compliance with Standards 1. The conceptual grading and drainage design for Old Town North complies with the City of Fort Collins storm drainage design criteria and the recommendations of the Final Report — Hydrological Model Update for the Lower Dry Creek Basin Master Drainage Plan. 2. The erosion control measures shown on the erosion control plan comply with the City of Fort Collins standards and generally accepted erosion control practices. B. Drainage Concept 1. The conceptual drainage design for Old Town North will be effective for the control of storm runoff with a considerable reduction in potential downstream effects. Page 9 Conceptual Drainage and Erosion Control Report Old Town North; Ft. Collins, Colorado a. Due to the project location within a currently defined floodplain, and due to the design constraints of existing drainage and irrigation facilities, the detention pond will be formed by berming along the north side of the Lake Canal. The elevation of the top of the berm will require that units adjacent to the pond be elevated to meet flood protection elevations. b. Release will occur through a headwall with an orifice plate to the Lake Canal. Release to the Lake Canal will be restricted 0.38 cfs / acre. Approximately 37 acres of the site will contribute to the pond. The remainder of the site will contribute to the proposed Dry Creek Channel located in Phase 2 of the project. The stormwater will be conveyed underground to the existing irrigation structure located in the Dry Creek Drainage. c. Preliminary pond grading has provided approximately 8.0 acre-feet VI. WATER QUALITY A. General Concept I. Water quality measures will be specified on the Drainage and Erosion Control Plan. Water quality measures will be provided in accordance with the latest details from the Urban Drainage and Flood Control District and the City of Fort Collins Water Quality Criteria. 2. Maintenance of water quality measures will be the responsibility of the contractor and the owner until the project is complete. The Homeowners Association will be responsible upon completion of the construction. Page 8 Conceptual Drainage and Erosion Control Report Old Town North; Ft. Collins, Colorado V. DRAINAGE FACILITY DESIGN A. General Concept The grading of the site will be done to convey as much of the stormwater runoff to the proposed detention pond. If any portion of the site cannot be graded to drain to a detention pond, the release rate will have to be reduced to compensate for the undetained flows or the flows considered in the design of the Dry Creek channel. 2. The detention pond will be located along the southern property line of the site. 3. Any swales that have slopes less than 2.0 percent will have 3' valley pans installed at the flow line of the swale. 4. The detention pond will be designed using the following criteria; a. Bottom slopes of 1 % or greater b. Provide valley pans for trickle flows and areas with a slope of less than 2% c. All side slopes will be 4:1 maximum d. Provide one (1') foot of freeboard for the 100-year storm event. e. Finished floors or lowest opening elevation of any building adjacent to a detention pond shall be set a minimum of 1.5 feet above the maximum Water Surface Elevation (WSEL). f. Release rates from the site will be in accordance with the recommendations of the Final Report - Hydrological Model Update for the Lower Dry Creek Basin Master Drainage Plan. B. Specific Details - Detention There are approximately 37 acres of the site that will contribute stormwater to the detention pond. Based on the allowable 0.38 cfs / acre release rate noted for this area in the Final Report - Hydrological Model Update for the Lower Dry Creek Basin Master Drainage Plan, we have estimated a volume requirement of 7.54 acre-feet. Page 7 Conceptual Drainage and Erosion Control Report Old Town North; Ft. Collins, Colorado 8. Detention will have to be provided in accordance with the .recommendations of the Final Report - Hydrological Model Update for the Lower Dry Creek Basin Master Drainage Plan. 9. Improvements within the area known as the "Product 6 Corridor" as defined with the Poudre River floodplain study, are not to increase the 100-year water surface elevation by greater than 0.10' a. The portion of the proposed southern access, between Vine Drive (existing) and the south side of the Lake Canal, lies within the "Product 6 Corridor". The design of this access will be provided so that there will be no rise in the Poudre River 100-year water surface elevation exceeding 0.10'. C. Hydrologic Criteria 1. Runoff calculations at various design points are based on the "Rational" method. The 2, 10, and 100-year storms will be analyzed with the Final Drainage and Erosion Control Report. All runoff calculations will be performed using the current rainfall IDF curves dated March 16, 1999. 2. Detention is proposed with this subdivision to accommodate the recommendations of the Final Report - Hydrological Model Update for the Lower Dry Creek Basin Master Drainage Plan. Detention pond release rates are defined in the report as 0.38 cfs / acre. This is taken from Table 4.2 in the Final Report. A copy of this table is included in Appendix II. D. Hydraulic Criteria 1. Storm sewer inlet design will be based on the inlet curves provided in the City of Fort Collins Drainage Criteria Manual. 2. Storm sewer design will be based on Manning's Equation with Manning's coefficients as suggested in the City of Fort Collins Drainage Criteria Manual. Page 6 Conceptual Drainage and Erosion Control Report Old Town North; Ft. Collins, Colorado B. Development Criteria Reference and Constraints 1. The alignment of Dry Creek in this area will ultimately be changed with the proposed re -alignment of Vine Drive. A grass -lined channel will ultimately be constructed along the south side of the future Vine Drive alignment. The channel section will parallel the south ROW line. Box culverts will be provided where Dry Creek crosses the future Vine Drive alignment and Redwood Street. Site grading along the channel will have to match the required channel section for the estimated design flows. 2. The design flow for the channel is 600 cfs. This design flow is based on discussions with the Stormwater Utility staff and on the assumption that the Upper Dry Creek Diversion Channel is constructed to divert flows around the Lower Dry Creek Basin. This design flow will have to be verified. 3. Redwood Street is currently platted. It was designed with the Evergreen Park development to the north. The actual street does not currently extend to Vine Drive. Street improvements currently terminate at the south end of the Meadows at Redwood. However, utilities have been installed in Redwood Street to Vine Drive. This results in a major design constraint issue for the conveyance of Dry Creek floodwater across Redwood. a. The existing approved design for Redwood Street obtained from plans prepared for Evergreen Park by VTN Colorado Inc; Plan approval Date by the City Engineer 03/27/74; VTN Project No: 172242. 4. The Josh Ames Ditch is currently utilized as a drainage conveyance for properties to the west, including some properties on the west side of North College Avenue. a. The Josh Ames Ditch release flows into the proposed detention pond. b. An overflow weir will have to be built into the detention pond weir that can safely pass the offsite flows brought in via the Josh Ames Ditch. 5. All proposed grading along the south property line will have to match the existing topography along the north side of the Lake Canal. 6. All proposed grading along the west property line will have to match the existing topography at the commercial sites. 7. All proposed grading along the east property line will have to match the proposed grading for the extension of Redwood Street along with the grading required to install the box culverts under Redwood Street for the Dry Creek realignment. Page 5 Conceptual Drainage and Erosion Control Report Old Town North; Ft. Collins, Colorado b. Development within the Poudre River floodplain is not allowed. B. Sub -Basin Description 1. The site slopes from the northwest corner of the site in a southerly manner to a low point located near the center of the south property line. 2. There is approximately seven (7') feet of fall across the site. C. HISTORIC CONDITIONS i. Historically runoff from the Old Town North site flows overland towards the Lake Canal. Until recently, stormwater was intercepted by the Josh Ames Ditch and conveyed over the Lake canal via a pipe. This no longer occurs as the conveyance pipe has been removed. The main existing concrete structure remains in place but is heavily damaged. 2. Currently, all storm runoff upstream of the Lake Canal is conveyed directly to the Lake Canal. Refer to the discussion under "Major Basin Description" concerning the intersection of the Lake Canal with the main Dry Creek channel IV. DRAINAGE DESIGN CRITERIA A. Regulations t. This conceptual report and the Conceptual Grading, Drainage and Erosion Control Plan for Old Town North were prepared in accordance with the requirements of the current City of Fort Collins Storm Drainage Design Criteria and Erosion Control Criteria and the recommendations of the Final Report - Hydrological Model Update for the Lower Dry Creek Basin Master Drainage Plan. 2. Approvals from the Lake Canal Company will be required for any storm drainage improvement proposed that affects the Lake Canal. a. The Lake Canal Company has requested that the stormwater from the detention pond be conveyed east underground and released into the canal at the existing concrete structure located in the Dry Creek channel rather than directly into the canal at the center of the pond. b. A preliminary profile has been designed that verifies that it is possible to convey the stormwater as requested. Page 4 Conceptual Drainage and Erosion Control Report Old Town North; Ft. Collins, Colorado 2. Old Town North has a platted area of approximately 45.01 acres. The site is currently vacant and is covered with native vegetation. 3. The Lake Canal runs along the south property line of the site. 4. The Josh Ames Ditch is located on the property and currently conveys stormwater from the west side of College Avenue across the property into the Lake Canal. III. DRAINAGE BASINS AND SUB -BASINS A. Major Basin Description 1. The entire site is located in the Lower Dry Creek Basin as delineated on the City of Fort Collins Stormwater Basin Map. a. The limits of the 100-year floodplain for Dry Creek were taken from FIRM map — Community Panel number 080102-0004-C; dated March 18, 1996. The limits of the 100-year floodplain for Dry Creek was also verified with the maps taken from the report prepared by Gingery and Associates titled Major Drainageway Planning - Dry Creek; Prepared for City of Fort Collins, Larimer County and Colorado Water Conservation Board; Prepared by Gingery and Associates; Dated April 1980. b. Development within the Dry Creek floodplain will require that all finished floors be elevated a minimum of 1.50 feet above the 100-year water surface elevation. Finished grades are shown for all the lots. 2. This portion of the Lower Dry Creek Basin is developed with a combination of residential, commercial and retail uses. There is some remaining open space at this time north of the site that will be developed in time. 3. The site is defined as sub -basin 410 in the Final Report Hydrological Model Update for the Lower Dry Creek Basin Master Drainage Plan. 4. There is a major irrigation structure placed in the Lake Canal in the Dry Creek channel. This crossing is located near the northeast corner of the proposed Old Town North development. The Dry Creek channel was essentially blocked with the installation of the structure. 5. Portions of the site are located within the limits of the 100-year floodplains of the Cache la Poudre River and Dry Creek. a. The limits of the 100-year floodplain for the Cache La Poudre River were taken from FIRM map - Community Panel number 080102- 0004-C; dated March 18, 1996. Page 3 Conceptual Drainage and Erosion Control Report Old Town North; Ft. Collins, Colorado . I. INTRODUCTION 1. This report presents the conceptual drainage and erosion control design for the proposed Old Town North site. II. GENERAL LOCATION AND DESCRIPTION A. Property Location 1. Old Town North is located in the south ''/z of the southwest ''/< of Section 1, Township 7 North, Range 68 West of the 6th P.M., Larimer County, Ft. Collins, Colorado. 2. More specifically, it is located on the north side of the Lake Canal, east of North College Avenue and north of Vine Drive and south of Conifer Street. 3. The site is bounded on the north by the future re -alignment of the Vine Drive ROW, on the east by Redwood Street, on the south by the Lake Canal and on the west by several commercial sites. The Cache La Poudre River is located south and east of the site. a. The proposed Vine Drive alignment is represented in the most current City of Fort Collins Master Street Plan. It is more specifically defined in the City of Fort Collins North College Avenue Access Management Plan. B. Description of the Property Old Town North is a proposed commercial / residential subdivision in the City of Fort Collins, Colorado. The project will be developed in 3 phases. Phases 1 and 3 will consist of the residential portion of the development. Phase 2 will consist of commercial development in the future. Phase 3 will occur after the delineation of the Dry Creek floodplain is updated. a. Phase 1 is within the currently defined Dry Creek floodplain. Phase 1 is outside the limits of the currently defined Dry Creek floodway. This will be the limit of development on this site until the Dry Creek floodplain is reviewed and amended to account for improvements made in the basin since the current floodplain was mapped. Page 2 Conceptual Drainage and Erosion Control Report Old Town North; Ft. Collins, Colorado TABLE OF CONTENTS I. INTRODUCTION................................................................................................. 3 II. GENERAL LOCATION AND DESCRIPTION ................................................ 3 A. PROPERTY LOCATION.............................................................................................. 3 B. DESCRIPTION OF THE PROPERTY.............................................................................. 3 III. DRAINAGE BASINS AND SUB-BASINS......................................................... 4 A. MAJOR BASIN DESCRIPTION.................................................................................... 4 B. SUB -BASIN DESCRIPTION......................................................................................... 5 IV. DRAINAGE DESIGN CRITERIA..................................................................... 5 A. REGULATIONS..........................................................................................................5 B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS ...................................... 6 C. HYDROLOGIC CRITERIA........................................................................................... 7 D. HYDRAULIC CRITERIA............................................................................................. 7 V. DRAINAGE FACILITY DESIGN...................................................................... 8 A. GENERAL CONCEPT................................................................................................. 8 B. SPECIFIC DETAILS (DETENTION).............................................................................. 8 VI. WATER QUALITY.............................................................................................. 9 A. GENERAL CONCEPT................................................................................................. 9 VII. EROSION CONTROL: ...................................................................................... 10 A. GENERAL CONCEPT............................................................................................... 10 VIII. CONCLUSIONS.................................................................................................10 A. COMPLIANCE WITH STANDARDS............................................................................ 10 B. DRAINAGE CONCEPT.............................................................................................. 10 IX. REFERENCES....................................................................................................11 Appendix I Preliminary Drainage Calculations Appendix II Portions of the Final Report Hydrological Model Update for the Lower Dry Creek Basin Master Drainage Plan; Prepared by Lidstone and Anderson; Dated September 10, 1997; Project No. COFC96.06 Appendix III Stuffer Envelope - Conceptual Drainage and Erosion Control Plan (1 Sheet) `+ _ CONCEPTUAL DRAINAGE AND EROSION CONTROL REPORT For OLD TOWN NORTH Ft. Collins, Colorado Prepared for: PALLADIAN CONSTRUCTION CO. PO Box 270053 Ft. Collins, CO 80527-0053 SHEAR ENGINEERING (PRINT DATE Prepared By: DEC 12000 SHEAR ENGINEERING CORP SHEAR ENGINEERING CORPORATION Project No: 1646-01-98 Date: December, 2000 4836 S. Colleee. Suite 12 Ft. Collins, CO 80525 (970) 226-5334 Fax (970) 282-0311 www.shearengineering.com Table 4.2. Summary of Subbasins for Which On -Site Detention is Required. Developed Condition Subbasin ID Area (ac)i Unit Release;Rates(cfs/ac) 401 14.2 (8.8)' 0.38b 406 56.9 (24.2) 0.45b 408 19.1 0.38 410 45.6 0.38 416 69.6 0.66 417 82.0 0.32 419 108.0 0.62 420 100.4 0.44 421 43.5 0.72 422 149.9 0.31 423 88.5 0.58 425 65.2 0.65 426 7.6 0.41 428a 35.7 (24.5) 0.39b 429' 16.3 (11.9) 0.54b 432 22.9 0.39 433a 24.9 (17.7) 0.40b 4343 85.6 (37.3) 0.32b 437 54.2 0.27 438 42.0 0.31 440 195.7 0.31 446 25.3 0.35 447 32.9 0.35 454 44.1 1.46 456 24.7 0.81 ' Undeveloped area is given in ( ) for partially developed subbasins. b For the undeveloped portion only. Based on 10-year historical runoff rates. MA