Loading...
HomeMy WebLinkAboutDrainage Reports - 10/04/1991Final Approved Report OPOF _✓W_ Date y FORTCOLMS u i i FINAL DRAINAGE REPORT i for i FAIRBROOKE FOURTH AND FIFTH FILINGS iFort Collins, Colorado May, 1991 I prepared by iNORTHERN' ENG =NEER=NG SERVICES , =NC . ' 420 South Howes, Suite 106 Fort Collins, Colorado (303) 221-4158 Northern Engineering Services, Inc. ' August 12, 1991 Mrs. Susan Hayes Stormwater Utility City of Fort Collins 235 Mathews P.O. Box 580 Fort Collins, Colorado 80522-0580 ' re: Fairbrooke Fourth Filing, Fairbrooke Fifth Filing Fort Collins, Colorado Project No.s 9113.00, 9114.00 Dear Susan: Northern Engineering is pleased to submit this Drainage Study for your review. It represents a study of the existing and proposed runoff characteristics of a site which has been previously approved by the City as Charleston P.U.D.. Soil erosion has also been included as an item of study in this report. The two filings of Fairbrooke are being included in one study because of their proximity to one another and because they are being concurrently developed. Your interest and input during the initial design of this project have been greatly appreciated. If you should have any questions or comments as you review this report, please feel free to contact me at your earliest_„gMAypnience. Sincerely, oN;�'�Q�t f.✓ T CJ C �i �� �►- t, = -ot25033 Michael F. Jones/1'.E.O.t"•(e� ION At 420 S. Howes • Suite 106 • Fort Collins, Colorado 80521 • (303) 221-4158 I .E Final Drainage Report for FAIRBROOKE FOURTH AND FIFTH FILINGS Forth Collins, Colorado August, 1991 I. GENERAL This report summarizes the results of a stormwater and erosion study conducted for the proposed development of Fairbrooke Fourth and Fifth Filings, located in Section 21, Township 7 North, Range 69 West of the 6th Principal Meridian, in Fort Collins, Colorado. Methods outlined in the City of Fort Collins' Storm Drainage Design Criteria and Construction Standards were used in the calculations for the stormwater runoff portion of this study, while the City's Erosion Control Criteria was used as a guide in preparing the erosion control plan. Additional references were made to the Urban Drainage and Flood Control District's Urban Storm Drainage Criteria Manual as needed. Summary calculations and other supporting material is contained in an appendix to this report. The Rational Method was used to calculate stormwater runoff from the site, while calculations based on the Modified Universal Soil Loss Equation (MUSLE) were used in the erosion study. II. SITE DESCRIPTION The project site is included in the Fairbrooke Master Plan as Tract B. (See Appendix.) It has also been approved as Charleston P.U.D. in 1985 and as Charleston P.U.D., First Replat in 1987. After the 1987 approval, a four-plex dwelling unit was constructed on the north side of Charleston Way near the east entrance to the r project. Two patio homes have also been built south of Charleston Way on a private drive. The tract containing the existing patio 1 homes is not included in the current project, but the existing four-plex has been included for platting purposes only. Fairbrooke Fourth and Fifth Filings Final Drainage Report page 2 II. SITE DESCRIPTION (Continued) The site is bounded on the east by a single-family development (Fairbrooke First Filing), to the south by the Pleasant Valley and Lake Canal, and to the west and north by Somerville Drive and Cedarwood Drive. The land slopes gently downward from northwest to southeast and is sparsely covered with weeds and wild grass. Charleston Way has been constructed through -the site and conveys runoff to the east into Cedarwood. (See attached Drainage and Grading Plan.) ' A small portion of the site drains southeast onto the backs of the adjacent lots in Fairbrooke First Filing. This area has been identified as Sub -Basin H1 in this study. A nine -foot wide grass lined swale was approved to intercept flows along the south boundary of Charleston First Replat and to convey them to a curb chase on Cedarwood. This swale was never built. Instead, a retaining wall was constructed adjacent to one of the developed lots approximately in the center of the swale easement and a six- inch perforated pvc pipe was laid next to the property line to carry flows from the southwest. (See Grading and Drainage Plan.) The remainder of the site contributes flows to the south gutter of Cedarwood Drive, where it flows eastward to a storm sewer inlet approximately 200 feet from the intersection with Charleston Way. This inlet has been sized to accept developed flows from the project site, based on a runoff coefficient of 0.50. III. PROPOSED IMPROVEMENTS The proposed development of the site will place 25 new single- family lots on approximately 5.6 acres, including the existing four-plex. Cul-de-sacs will extend north and south from Charleston Way to provide access to some of the lots. The five lots facing onto Cedarwood Drive are to be platted as Fairbrooke Fourth Filing, while the remainder will be included in the Fifth Filing. Proposed over -lot grading will convey runoff flows from the Fifth Filing into the interior streets and from there into Cedarwood. A small area of the back lots to the south and east will continue to drain towards neighboring lots, but these flows ' Fairbrooke Fourth and Fifth Filings Final Drainage Report page 3 III. PROPOSED IMPROVEMENTS (Continued) will be substantially reduced from existing. Runoff from these 1 rear lots will be collected in a concrete pan and conveyed to the southeast corner of the Fifth Filing. From this point, a concrete pan is to be constructed in the existing 10-foot wide drainage easement which extends to Cedarwood. A curb chase is to be constructed where this pan empties into the street curb. Runoff from the Fourth Filing will be directed into Cedarwood 1 Drive to the north. These flows, along with those from the Fifth Filing, will be conveyed to the storm sewer inlet east on Cedarwood. The Master Drainage Plan for Fairbrooke used a runoff ' coefficient of 0.50 for this area. Since the calculated composite runoff coefficient for the site is somewhat less at 0.46, the site should work within planned drainage parameters. Flows will leave the site undetained and eventually reach a regional detention pond at the southwest corner of Prospect and Taft, where capacity has been provided for this site. (See attached Fairbrooke S.I.D Drainage Report.) Monitoring wells -have been placed adjacent to the Pleasant Valley and Lake Canal and a log of groundwater depths is being kept by the developer. Prior to construction of the second phase of the Fifth Filing, groundwater conditions will be evaluated and a determination made regarding any protective measures, such as foundation drains, that may be deemed necessary. IV. EROSION CONTROL It is anticipated that the project will be built in three phases, beginning with the Fourth Filing, then the area of the Fifth which lies north of Charleston Way, and finally the area south of Charleston. The first phase should commence in August of 1991 and will consist of over -lot grading only prior to placing buildings on the lots. The developer plans to grade the lots individually as they are built out and, therefore, be able to eliminate the intermediate step of seeding prior to the finished lawns being established. It is recommended that. if the lots are to stand any longer than thirty days between grading and start of house construction, that seed and dry mulch be applied to prevent wind. or rainfall erosion from becoming a problem. It is also recommended that gravel filter ' Fourth and Fifth Filings Final Drainage Report page 4 IIV. EROSION CONTROL (Continued) ' dikes be placed in the street gutters immediately downstream of any construction areas and that the condition and effectiveness be monitored. This should be done on all three phases of the project. The Fourth Filing is anticipated to be completely built out by January of 1992. The second phase of the project is expected to commence in September of 1991 and be built out by spring of 1992. The only public improvements proposed will be the north cul-de-sac of Rutledge Court. Due to the small amount of surface disturbance, no major erosion protection structures are planned. It is recommended that several gravel dikes be temporarily placed in the gutter downstream 1 of the cul during construction and that these structures be maintained and monitored for effectiveness during that time. Lot grading is proposed to be done individually, as above. The third and final phase of the project is expected to begin in the spring of 1992 and be completed by the following fall. The proposed public improvements will consist of the south cul-de-sac of Rutledge Court. Again, gravel dikes should be placed in the gutter of Charleston Way to filter runoff during construction of the cul. Due to the extensive over -lot grading necessary for this phase of the development, the developer proposes to seed and mulch this area within two weeks of completion of the grading to control wind and rainfall erosion. The proposed seeding and mulch must comply with current City standards for erosion control, as set forth in Section 11 of Storm drainage Design Criteria and Construction Standards. The proposed schedule for construction would have the proposed seeding and mulching take place during "Cool" seasons, so the proposed grass planting is chosen accordingly. Should the construction schedule be revised, the developer can alter the seed mix to suit the season in which actual seeding takes place. For the expected construction, it is recommended that a mixture of 55 % Fairway Wheatgrass, at 7.2 drilled pounds per acre and 45% Smooth Brome at 16.1 drilled pounds per acre. FA I RBROOKE FOURTH / FIFTH F I L =NG SITE HYDROLOGY Basin Design Exist. Dev. Point Area Q2 Q100 Q2 Q100 (Ac) (cfs) (cfs) (cfs) (cfs) ------------------------------------------------------------ Site, hist. 3 6.92 4.86 17.92 Site, dev. 3 6.92 5.41 18.70 H1 1 0.97 0.67 2.44 D1 1 0.36 0.18 0.63 D1, FBK6 2 0.51 0.26 0.89 D2 4 2.93 2.29 7.92 D3 5 1.89 1.48 5.11 D4 6 0.94 0.73 2.54 NOTES: 1. Historic Sub -Basin H1 contributes flows to east and south as sheet -flow; no existing point release. 2. FBK6 refers to portion of 4-lot area of Charleston First Replat which contributes flow to pan at Design Point 2. 3. Sub -Basins D-2 and D-3 are portions of site which contribute to street flows at Design Points 4 and 5. 4. Top of foundation elevations to be a minimum of six inches above noted finish grade. 5. Detention is provided in the existing Fairbrooke Regional Detention Pond. 6. Minimum building opening elevations for lots 5 trough 12 are to be six inches below the top of foundation. 7. See Drainage Report for erosion control methods, scheduling and other information. 8. Prior to construction of the second phase of the Fifth Filing, groundwater will be monitored adjacent to the irrigation ditch and a determination of protective measures, if any, will be made with the assistance of a qual.ified soils engineer. APPENDIX 1. Runoff Calculations ................................... 1 2. Erosion Control ....................................... 6 3. References ............................................ 9 4. Fairbrooke Master Drainage Plan ....................... 15 5. Charleston First Replat Drainage Plan ................. 21 ►, r-1 0, -z s -7zzc� o,25'" C/n G _ ry�� T I : o. 3 7 r e _o L- z�� 5- Z,5 �e c= b,zs �N z �� c. - sow s : •� -sue v ti i-�r3'�oiZrc. Go�va,-7� oas Ccq,u�� N�en, C437) OIZ5) `, Z, S v73 1vA3 it �- I �A1�LFSTLO�Y� ,rj� � ��ve�vp� �,al.tar�•lo►s4 , 3. 5�� l�as�� �-z .CGo.�-�n.�13.,�•o sa,7"(H .5�r3-��54�-3 5 • ��i Coiv'�7..� 3 F�'w � O P^_.,cf • �-� 1C : !o ", O. � S Ac iZ '(� -Q�-7 r4IITS �. �`V14-0P&-n� Sr 2. �.. D, P.i IN<I o . S o M �ativ r� 2. �. Ge,b A u1 0 ,� 0 E � S-T �} L o -� s �13L cT") ®, S-�ticz.1 y �,31 Ac c_ a.95. Zz7 75 S, Lea w we.zo (TLp-(r o N. - — - - ' KA C3 - WN 4,4 -� z pint .5o 4A-51.•N: i� �. ►,�, r L3 z - -- - 1 ELOA - ' T O. p�Pt o 1G r= 51-14 DITIO d / �. �vND cpZ No Text No Text C"o <32 0 CF F to rz,1 1 w 4; L-J Aa 1 JJJ _ , o.3 LS Co c) : i�o�.�.rJzz'.. ' v �a,a /A, LO CS] li'j S._ B� cv+4.F�E✓� �an9 i 1 zi No Text RAINFALL PERFORMANCE STANDARD EVALUATION ------------- PROJECT: --------------------------------------------------I ►rL}71Z-c:o STANDARD FORM .A. 'I COMPLETED BY:. r DATE_ ----------------------------------------------------- DEVELOPED ERODIBILITYI Asb Lsb I Ssb Lb -------�--- I Sb I PS SUBBASIN ZONE I (ac) (ft) I (%) (feet) --------- a r8 F a- ----- ----- M p -------i----� o' q3 I S z 3s -------- '2 . It a -------I-------I-------I 3951 z l- l I l .D• 3 I F�o0 1, 39 I 1 tl/q 16o7 D--Z M o� I� 2,93I Z3o � z• �- I�, I �. 7 � I �G 175,�t + l I __ I I DI/SF-A:1989 I EFFECTIVENESS CALCULATIONS PROJECT: F 1-d 4 $ - --- COMPLETED BY: F STANDARD FORM B DATE: 13.9 1 ..Erosion Control C-Factor P-Factor Method Value Value Comment �/k1 ----------------------------------�Qs ---- 1 ,o C. Nam: A) * at � 8s'��.It 3 b M S IM Uey r4 V s. C--k+' SAN / MJl.cy I capI� D 9 Awl Co4zD,v45 00G t,DO 1Ayti2T-W 7 p 47tio0"V P%&"T 1,00 t6o I) 72147one. ?,I/ "G2a$/e� $G 8A,f%A. (�AOJ/V� .(� 99 ,,V CoN-(Roy �'InVJ4•" ----------------------------------------------------------------------I MAJOR, PS SUBAREA 1 BASIN (%) BASIN (Ac) CALCULATIONS ----- >7z ------ ----- F8 q.- ------ o,93 ----------- Cu=CL.3���/w f 647) Lc5 t (-)4) $S71 -I srTa 75, `I ------------ DI/SF-B 1989 2,93 +(Z,s3)sM t I4)H;5�1 ZA �i,•}���ot��.�z,53�(.ov>'I'r!i��(I.0)�'tZ o,o9g PW&l d 0 4 3 i3 E CONSTRUCTION SEQUENCE 0 PROJECT:- ") - m'moolgz s SEQUENCE. FOR 19 ONLY COMPLETED BY: STANDARD FORM C DATE: 5. 31-`j Indicate by use of a bar line or symbols when erosion control measures will be installed. Major modifications to an approved schedule may require submitting a new schedule for approval by the City Engineer. ' YEAR MONTH ---------------------------- ' OVERLOT GRADING WIND EROSION CONTROL ' Soil Roughing Perimeter Barrier Additional Barriers Vegetative Methods ' Soil Sealant Other RAINFALL EROSION CONTROL STRUCTURAL: Sediment Trap/Basin ' Inlet Filters Straw Barriers Silt Fence Barriers ' Sand Bags Bare Soil Preparation Contour Furrows Terracing ' Asphalt/Concrete Paving Other cu29 DIc2S VEGETATIVE: Permanent Seed Planting) ' Mulching/Sealant Temporary Seed Planting Sod Installation Nettings/Mats/Blankets Other, I r�[q► r9�ti I A !s t o l,y I o J l l IA Ikl I�l � B��( 1�0 s tie R yl�i t o VL D im i COU r �V VTPAk, At� STRUCTURES: INSTALLED BY MAINTAINED BY VEGETATION/MULCHING CONTRACTOR DATE SUBMITTED HDI/SF—C:1989 APPROVED BY CITY OF FORT COLLINS ON Q et F,c.iti,4 p4r-%5e 7M: a- 5I ILQ : vt.,105 0F ouc:n, 1=l C,rzkhpI1a4 rGa )114E-1-4c.l;.�L 4, I"DrL Go c�" = UnIaya� DI STJt lc-� `r (�703b"-O7z.1+1 i/�q .ti14-ci Z �F, GT7 1 3,I�G pc g TY,2.cac, ; Fic, 3.z Cam--` 7. GT / § 3:Z. 1 P 5 3 -5 ��►-� jrac+Ie>� Fri-D SJQ-14 Rl�� P ` /0 -( IAe--FtZZ)) -'tTt-I �_ k5 4- 1 4--z C/- r+ICLr) 1 1 1 1 1 City of Fort Collins STORM DRAINAGE DESIGN CRITERIA • 3.1.6 Runoff Coefficients The runoff coefficients to be used with the Rational Method referred to in Section 3.2 "Analysis Methodology" can be determined based on either zoning classifications or the types of surfaces on the drainage area. Table 3-2 lists the runoff coefficients for the various types of zoning along with the zoning definitions. Table 3-3 lists coefficients for the different kinds of surfaces. Since the Land Development Guidance System for Fort Collins allows land development to occur which may vary the zoning requirements and produce runoff coeffi- cients different from those specified in Table 3-2, the runoff coefficients should not be based solely on the zoning classifications. The Composite Runoff Coefficient shall be calculated using the following formula: C = (MC,A,)/At Where C = Composite Runoff Coefficient CI = Runoff Coefficient for specific area A, At =Area of surface with runoff coefficient of C, n = Number of different surfaces to be considered A, = Total area over which C is applicable; the sum of all A,'s is equal to At Table 3-3 ' RATIONAL METHOD RUNOFF COEFFICIENTS FOR COMPOSITE ANALYSIS Cheracterof Surface Runoff coefficient Streets, Parking Lots, Drives: ' Asphalt................................................................................................ 0.95 Concrete............................................................................................. 0.95 Gravel................................................................................................. 0.50 Roofs.......................................................................................................... 0.95 ' Lawns, Sandy Soil: Flat<2%............................................................................................. 0.10 Average2 to 7%.................................................................................. 0.15 Steep>7%...........................................................:.............................. 0.20 Lawns, Heavy Soil: Flat<20/6 .......:................................................ ..................................... 0.20 ' Average 2 to 7%.................................................................................. 0.25 Steep>7%......................................................................................... 0.35 ' 3.1.7 Time of Concentration In order to use the Rainfall Intensity Duration Curve, the time of concentration must be known. This can be determined either by the following equation or the 'Overland Time of Flow Curves" from the Urban Storm Drainage Criteria Manual, included in this report (See Figure 3-2). Tc=1.87 (11 — CCd D1/2 S.1 ' Where Tc =Time of Concentration, minutes S = Slope of Basin, % C = Rational Method Runoff Coefficient ' D = Length of Basin, feet Ct = Frequency Adjustment Factor Time of concentration calculations should reflect channel and storm sewer velocities as well nc nvurlonri flnu, fimnn 3.1.7 Time of Concentration In order to use the Rainfall Intensity Duration Curve, the time of concentration must be known. This can be determined either by the following equation or the "Overland Time of Flow Curves" from the Urban Storm Drainage Criteria Manual, included in this report (See Figure 3-2). Tc=1.87�,) —CCD1/2 S Where Tc =Time of Concentration, minutes S = Slope of Basin, % C = Rational Method Runoff Coefficient D = Length of Basin, feet C, = Frequency Adjustment Factor Time of concentration calculations should reflect channel and storm sewer velocities as well ' as overland flow times. 3.1.8 Adjustment for Infrequent Storms The preceding variables are based on the initial storm, that is, the two to ten year storms. For ' storms with higher intensities an adjustment of the runoff coefficient is required because of the lessening amount of infiltration, depression retention, and other losses that have a proportionally smaller effect on storm runoff. These frequency adjustment factors are found in Table 3-4. ' Table 3-4 RATIONAL METHOD FREQUENCY ADJUSTMENT FACTORS ' Storrs Return Period Frequency Factor (Yeafs) G 2to10 1.00 11 to25 1.10 - ' 26 to 50 1.20 51 to 100 1.25 ' Note: The product of C times Cf shall not exceed 1.00 3.2 Analysis Methodology The methods presented in this section will be instituted for use in the determination and/or verification of runoff at specific design points in the drainage system. These methods are (1), the Rational Method and (2) the Colorado Urban Hydrograph Procedure (CUHP). Other computer methods, such as SWMM, STORM, and HEC-1 are allowable if results are not radically different than these two. Where applicable, drainage systems proposed for construction should provide the minimum protection as determined by the methodology so mentioned above. 3.2.1 Rational.Method For drainage basins of 200 acres or less, the runoff may be calculated by the Rational Method, which is essentially the following equation: Q = CtCIA ' Where Q = Flow Quantity, cfs A = Total Area of Basin, acres Cf = Storm Frequency Adjustment Factor (See Section 3.1.8) ' C = Runoff Coefficient (See Section 3.1.6) 1 = Rainfall Intensity, inches per hour (See Section 3.1.4) 3.2.2 Colorado Urban Hydrograph Procedure For basins larger than 200 acres, the design storm runoff should be analyzed by deriving synthetic unit hydrographs. It. is recommended that the Colorado Urban Hydrograph Procedure be used for such analysis. This procedure is detailed in the Urban Storm Drainage Criteria Manual, Volume 1, Section 4. MAY 1984 3-5 DESIGN CRITERIA low ■■■■■ ■OMME 1 1 1 1 1 DRAINAGE CRITERIA MANUAL 5( 3C 1- 20 Z W U W IL 10 Z W IL O 5 W ¢ 3 Z) O V 2 c W 1- 1 RUNOFF mill i■ �.,""_ �l•�� mil;•■■� 5� •2 •3 •S 1 2 3 5 10 20 VELOCITY IN FEET PER SECOND FIGURE 3-2. ESTIMATE OF AVERAGE FLOW VELOCITY FOR USE WITH THE RATIONAL FORMULA. *MOST FREQUENTLY OCCURRING "UNDEVELOPED" LAND' SURFACES IN THE DENVER REGION. REFERENCE: "Urban Hydrology For Small Watersheds" Technical Release No. 55, USDA, SCS Jan. 1975. 5 -1-84 URBAN DRAINAGE & FLOOD CONTROL DISTRICT E3 1_5, ' , .. e 91+LBL TP.APP 51 ENTERt y 02 .h M. 52 53 / 1- . b �I 03 PROMPT 54 RCL 06 . 94 STO 00 55 X<?Y 95 •Z ?' 56 YtX N = /Aaa�s w5 s n 06 PROMPT 97 STO 01 57 ENTERt Be •N ?• 58 RCL 04 PROMPT 9 SORT 59 N c g 10 STO 02 * 61 1.486 Y ^► ppe 11 'S ?' 62 12 PROMPT 63 RCL 02 13 STO 04 caN Ugh 14*LBL 01 65 RCL 05 • ' IF Q o'1 5 Y '+' - 15 'Y ?' 66 * lr,a rL►e--n< +6 PROMPT 67 STO 97 ,;Tn @, 68 .h. . r, prL 93 l y c a 1 69 ARCL 00 /�V,, nl r►1►.4 q s ,a * 79 XEA 03 1 RCL 9F� 71 "Z . ' 72 ARCL 01 I, n A Q/35��~ _ RCL 9' 73 XE9 03 74 •N: ' N� " STO 85 75 ARCL 02 h RCL 93 76 XEO -03 'S: ' 27 RCL 01 * 77 78 ARCL 04 28 29 RCL h'.' 79 XE9 03 'Y. bar t� 30 + 88 31 RCL 93 81 ARCL 03 32 * 82 XE9 93 33 STO 06 83 'A' 34 RCL 01 84 ARCL 07 TZ p X12 85 XEO 0335 Q G . 3i 86 RCL 07 37 + 87 RCL 95 38 SORT 88 i 39 RCL 03 89 •y. . 99 ARCL X 40 * 91 XEO 83 92 P.PV 42 * 93 GTO 01 43 RCl 00 +LR- 9; 44 + 4` FNTERt 4k QF 97 5 Q. 47 X<`Y 98 RTN 48 99 END 49 Ti1 P�, S ' 50 2 1 1 f 1 1 1 1 1 1 1 1 1 1 10000 9000 8000 7000 6000 5000 4000 2000 -1000 00 e00 700 x eo0—_ ; 500 p 400 Q300 200 MAY 1984 100 90 so 70 60 50 40 30 20 10 From BP r — L EQUATION: 0 • 0.56(A) s" JP1 0 IS NOUGHNEBB COe1FICIENT IY YAYNIwO FORMULA APPROPRIATE TO MATERIAL IN BOTTOM OF CNAMn" A H NECIPROCAL OF CROSS SLOP[ REFERENCE+ H. A. I PROCEEDINGS It". not Im EQUATION 11A1 EXAMPLE (set DARNED timum GIVEMI A 0.03 i • 14 i /r1-•-I[CO Iwo, a •2.0 CFS rn f/ ll � 30 U- .10 .08 .07 .05 .04 2.0 IN 80 70 60 50 LL .40 ? 3 Z - .30 -- :_ — .02 ^ cy---- \ .3 N 20 R W INSTRUCTIONS -�--� .OI all 1. CONNECT i/n RATIO WITH slot[ 1!1 •1 .0 H. AND CONNECT DISCHARGE 101 WITH = O3 008 DEPTH Ill. THESE TWO LINE! MUST Q 'U INTERSECT AT TURNING LINE IOU y, .02 S .007 COMPLETE SOLUTION' Q .01 I1 V .006 E. FOR !HALLOW _ __ J V-SHAPED tL .005 CHANNEL p AS SHORN USE NOMOGRAPH WITH I. T .004 T W a 3. TO DETERMINE 0 ii p .003 J DISCHARGE 0, IN �, D ,w PORTIOw 01 CMANNEL HAVING WIDTH E: :[T[RMINE D::TH J 100 TOTAL DISCHARGE IM .002 [:Ting ![CTIOM e. THEN USE NOMOGRAPH TO OETENY//ISSNE1 00 IN SIC' -OFF O FOR 11I1H J'J-4) A,to OETERYIM[ OISCHARGE T J IN COMPOSITE SECI.::O- J Y FOLIO: INSTRUCTION ! 1 }F f�1� TO OBTAIN DISCHARGE IN .001 SECTION a AT ASSUMED •l�lJ-J'1 DEPTH J I OBTAIN 0A FOR SLOP[ RATIO 1, AND DEPTH l THEN 0,. G, . OP Figure 4-1 NONOGRAPH FOR FLOW IN TRIANGULAR GUTTERS (From U.S. Dept. of Commerce, Bureau of Public Roads, 1965) 4-3 Z IL (n .10 W IL W oe W .07 06 p .05 m .04 V .03 Q ~ .02 a W C 01 DESIGN CRITERIA 1 MAY 1984 .9 .8 .7 LA- Cr .6 U. Q Z . 0 5 U D 0 W .4 Cr .3 .2 rel 0 2 4 6 8 10 12 14 SLOPE OF GUTTER M) Figure 4-2 REDUCTION FACTOR FOR ALLOWABLE GUTTER CAPACITY Apply reduction factor for applicable slope to the theoretical gutter capacity to obtain allowable gutter capacity. (From: U.S. Dept. of Commerce, Bureau of Public Roads, 1965) 4-4 DESIGN CRITERIA PAGE 23 I,+ � 1 I o I col000 I I I et Ln Ln I 10 0 0 co 0 0 1 1 _ 1 O I CL Ct O Ct C C C 0 0 0 1 1 I O I C• C• C• C• Lo Ln Lo Ln Ll U; ' t C• I 000 CO OOOOOO I C I 0 C1 Ct Ct 01 C1 Ct C1 Q1 C1 Oi Cl O CD CD 1 1 I .O 1 et C• C• � C'C• C' et�et C'C•Ln Ln L.n 1 M 1000000 CC OOOOOOO 00 1 CD1 1�-00 co C1 O Ct O C1T C1 m Ci m at C1 C1 01 Ct C1 1 O 1 et C" et C• C• o- f co co cc co co co C...' 00000000000000000000 1 1 I O I CMC' LO t0 t0 tp to r.,r� PI r-_t\ r.,r., � r., r., r., r.- 00000 co 1 1 1 I O I C•�ItTC•C•etC•C• C'et et C• C• C'et C• et et et C• mr 4 et 444 co co co co co co 00 00 00 co co 00 co co co co co co co O co co 0000 1 1 1 O 1 0 N M C' Ln to Ln 1 0 1 0 tp t0 t0 l0 r\ n f\ n n ^ n r- 0 0 0 O 1 CL 1 M C• C' C• Ct C• er C- -01 C' C• et et et Q' C• C• C• C• eh et C• C• tt ; C• cc I 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O 1 O 1 to O N M d' C-Ln Ln Lo U1 t0 t0 t0 t0 t0 t0 t0 ko t0 t0 (-I ?-I` r1� r., r.,O i 0 i mmr-crC•C•C•C•etetcccetccceretvicercerccet U I 10 0 0 0 cc 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Ln 1 O i etM rN MM er•C•C lc:r LO Ln Ln Ln Ul) to Ln Ul Ln t0 t0 t0 t0 t0 t0^ Mm et C•et et c et C•C'C"�C•C C'C•ct C•eY C'et C•et C'd•et 10000000 C 00000000000000000000000000 J 1 O I Ot000 O.-r.-+NNMMMMet et C• C' C•Ch C• C' U, to Ln Ul tO to O 1 1 U 1 t0 1 M m M C• C• C• C• V -*- C• et et C' C• C• C' C• et C' C• et C• eF et i 00 co co 000000 O 00 c000000o O 00 OO co co O co co co co co co co C i 0 1 ONLn r-_ co Ct OO.-+.-+.-+NNNNNMMMMM-trC'C'C•C- W 1 vLn 1 N M M M M M C' C' et et C• C' C' C• et C• C• C• C• C' et -cr C• C' C' C' I I 0000000000c0O=cococccoOOOOOOOOOOOOO ' O 1 a. Ln I .-1 co 14 M C'Lrl of tO tO t-_ r-I f� co co O O cc 0O10n CnCCOOO W I O: • I I J C• I N N m c M M cn M m M M C4 M C4 M C4 C4 C4 M M CM; M C' C' e t• 7 e t N 114 1 0'000000000000000000000000000000000000 � 1 1 0 1 O 1 L0 to co O.•-I N M et d Ln Ln In tD t0 t0 t0 t0 r-- r., 1�� co co 0 C1 rC1 O I of I r NNMMMm cn MM Mcn en M M M C4 f"'f M_ cl; C4 M M C" C4 C4 Z I I 00 0000 00 00 00 00 00 00 00 00 00 co 0 0 0 0 0 0 00 000 0 Q 1 H 1 In 1 r .-1Inn04=0.--1NN M M M C• C' et C' C' LO Ln Ln%Q t0 t01�1-1 tN 1 1 1 M I. N N N N M M M M M M M M M M M M M M M M M M M M M W I 1 00O0000O00O00Oc000000C00OOOOOOOOOOOO Q I O I MNto co cn (I- +NNML•9 m et C C• • eet C• t Ln Ln Ln LO tp t0 L0 L0 1 M I 1r r+NNNNNNNNNNN NNNNNNNNNN C I 1 0000000000rw000000000Q0000OOOO000000000000 O 1 1 U- I to 1 Ln LO C% N M et Ln t0 n n n Co Co Co C1 C1 C% 4M M C1 O O O O O 10 C I 1 W 1 N I CL O O .- 4 .-+ rL ...--1 r .--4 . N .--1 .--1 N N N N N N d 1 I r- 000pO 0 co O co co co O co co co co co O 000000 O co O O 00 co 1 O 1 :r Ln O M Ln 1.0 co 0 0� 4= O O .-1 .-1 .-1 .--r N N N N M M M L`•) M M iN I 0 C1 O O O O C O O .-+ .--1 .--1 .-1 .� .•+ ...-+ '-+ .--I r-1 '-I .-r .--1 .-r r-1 r-I I 1 1� n 00 00 00 00 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 000 1 1 1 Ln 1 ONO.--r Z7 U1 rwl r%0 01 C$O O14 .-1 Nr+.-.NNNMMMMM 1 1 1 ►•1 I t0O 0 C1 C1 CL C1 C1 CO1 C1 C1 00 00 O O 00 O O O O 00 I 1 r, r., r., r, ' r, 1� r� r� r., 0 00 0 0 0 0 0 0 00 0 00 0 1 CD L0 MO et 1�C10.-�N M M et et Ln Ln Ln Ln t0 t0 to t01-I 1., t0 t0 t0 I c Lc r-: n r� r_ p O O O O O O O O O O O O 0 O O O O OO I I n n r\ ^ f\ n n l\ n r\ n n r\ n n r-. f\ n r\ r\ r\ f\ f\ n f\ f\ 1 1 t Ln 1 CLOC•t0^OOr-I^n%0 t0 t0 LO C'C' L•" f MNNC1 tp C'.-L M L0 1 • I . . . . . . . . . . . . • 1 O I O N N N N N N N N N N N N N N N N N N N'-I r-1 .-•1 N O O 1 I f\n nr-I nn nn nn^nnn^nf-,n r-,nf\r\n^^n I S 1 1000000 C 0000000000000000000 I O C7 H I O O O O O O C O O O O O O 0 O O O O (D O O O 0 O O O 1 JZLr_ I �NMetlnLDr�wmC) -4"m-I:•LO%Df\OQtOLOOLnOLOa 1 U- W 1 Ln I J I TABLE 5.1 1� I I I I 1 I I I I 1 FINAL DRALNAGE REPORT FOR FAIRBRO01::E:. G. 1. D. CITY OF FORT COLLINS COUNTY OF LARIMER STATE OF COLORADO Novembere,lC?83 Prepared by: Parsons & Associates Consulting Engineers 432 Lint-, Lane Plaza Fort Collins, Colorado 80524 Project Number 03..18 WOR 0 FINAL STORM DRAINAGE REPORT FAIRBROOKE S.I.D. i FORT COLLINS,'COLORADO GENERAL This report, in combination with the Drainage Map accompanying this report, the Fairbrooke S.I.D. Design Plans, the _Brown Farm Preliminary Master Drainage Plan (Sheet 18 of 18) prepared by R. V.-Lord and.Associates, Inc., August, 1971, and Volume II "Preliminary.Design Report --Diversion of Storm Water Runoff Through Irrigation Canals from Mulberry.Street to Spring Creek --Fort Collins, Colorado", prepared by Resource.Consultants, Inc,, July, 1980, is intended to describe the procedures and results of a . drainage study of stormwater runoff generated by this project and adjacent properties. The proposed development along with the required.drainage improvements are analyzed in accordance with the guidelines established by the City of Fort Collins' Storm Drainage Criteria Manual. INTRODUCTION The purpose of this study is to determine the quantity of stormwater runoff.generated from the development of the various tracts within the Fairbrooke site, along with adjacent upstream property, the manner by which this runoff will be accommodated by the Fairbrooke project, and how this relates to previous studies.as outlined above. SITE DEri(::Rir71l0N The site is lociAted in the nothrar- 1/2 of Section 21, Township 7 North, Range 69 West, of the 6t:.h F: incipal, Meridian, Stare of Colorado, County of Larimer, Cit.y of Fort Collins. The Fairbrooke project consists.of 99.42 acre.. mware or less and is bounded by Prospect Street on the north, Ta-rt Hill Road on the east, 'The Brown Farm development and Aspen Heights P:U.D. on the south, and the Foothills' West development to the west. The site is presently undeveloped and is used primarily for agricultural purposes. The.existing drainage pattern is to the north E.,nd east at slopes ranging from 0.8 to 10 percent. The Pleasa;-,t Valley and Lake Canal flows through the property -from north to OLlth. PROPOSED LAND USE The project is planned to consist of tracts on which varying proposed land usages.will occur. Several of the tracts will have townhomes and patio homes with densities ranging from 6 to 7 1/2 l-) units per acre. Other tracts are proposed for apartments on which the density will vary from a to 12 units per acre. The remaining tracts will be used for a day care center, a church and a detention pond. HYDROLOGIC ANALYSIS The Rational Method has been utilized to generate stormwater runoff 'flows for the 2- and 100-year developed return period storms for the various tracts in Fairbrooke. The Drainage Map defines the basin boundaries and the design points, and Table 1 summarizes the results 'of the hydrologic analysis of these sub -basins. In addition, offsite stormwater from the Brown,Farm development contributing runoff the the open channel along the south side.of Fairbrooke west of Hampshire Road and the runoff in Hampshire Road have been ' estimated. It should be noted at this point that the calculated flows in Fairbrooke are, approximate due to the fact -that the interior drainage patterns (street layout and building locations.) within the individual tracts have not been established. The calculated runoff 'quantities, however, assume fully developed conditions using a runoff coefficient of 0.50 concurrent with the existing RL L& RP zoning. The -P atter.ns of flow and the basin.,configurations as contained herein should be maintained.when actual development occurs so as to not adversel y.affect the improvements s proposed with the Fairbrooke Special 'Improvement pistrict. DETENTION The detention pond for Fairbrooke Special Improvement District will be designed by the City of Fort Collins Storm Drainage. Division, and is not included as part of this report. W 2 d • Y ~ ~ — z = a C/J r- k o� o N W0`$ O N it u. p a air M oo M F `i W US r LL 1 O y a I W w a 3E m W p o 0 m s m w a LL I r oil lllIE-111 ER I �9NIIIII IENIN111111111110 0 OEM MEN ZL FINAL"DRAINAGE REPORT FOR CHARLESTON P.U.D. FORT COLLINS, COLORADO JUNE, 1987 Prepared by: Parsons & Associates Consulting Engineers 432 Link Lane Plaza Fort Collins, Colorado 80524 (303) 221-2400 Project No. 85.12 CAR 'L FINAL DRAINAGE REPORT FOR CHARLESTON P.U.D. This report summarizes the procedures and results .of a drainage study of §tormwater runoff from the proposed.Charleston Planned Unit Development (P.U.D.). The project site consists of 6.27 acres of undeveloped land which is bounded by Somerville and Cedarwood Drives, the Pleasant Valley and Lake Canal, and Fairbrooke-First Filing, a residential subdivision. The site is part of a larger area, the Fairbrooke Special Improvement District (S.I.D.), which already has an approved drainage system. Stormwater runoff from Charleston P.U.D. will mainly be carried as gutter flow in Cedarwood Drive to a point where it--will-enter-the existing storm sewer system of Fairbrooke F.irst.Filing. Calculation of the Rational Method...C.oef.ficient, C.,.._ shows a slight increase from that assumed for the S:I.D.. The new grading configuration has changed the time of concentration from what was calculated in the S.I.D:-. This has-- caused a slight increase in the site runoff. _ Detention requirements for Charleston P.U.D. are provided in the regional detention pond which has been provided as part of the S.I.D.. No on -site detention has, therefore, been provided. CONCLUSION The proposed land use change and subsequent regrading have resulted in a slight increase in the 2-year design runoff. The existing downstream drainage facilities, per Fairbrooke First Filing, were doubled in inlet capacity from what was originally proposed in the Fairbrooke S.I.D.. The Fairbrooke S.I.D. required 2-4' inlets; Fairbrooke First Filing doubled the openings to 4-4' inlets. We feel that the slight increase in site run-off (0.7 cfs) from what was projected in the Fairbrooke S.I.D. will be handled by the existing oversized downstream drainage facilities in Fairbrooke First Filing. Therefore, no off -site modifications will be needed. Prepared under the direct supervision of: Donald M. Paksons, P.E. Colorado Li ense # 13131 '9�g�MY�'� o;0sp a, 13131 M C'o rv,. �J`��ONAI �.i6•�PO�r 411.1 •....•��. OF CT _,,o•� �I I . a OL W Noon 1 CHARLESTON P.U.D. DEVELOPED SITE HYDROLOGY - c Q2 Q100 Design Pt. Basin Area 1 A 0.25 Ac 0.50/0.63 0.27 1.00 1.1 4.1 ' 2 B 0.93 Ac 0.54,Ac 0.50/0.63 0.50/0.63 0.50 3 C 0.20 Ac 0.50/0.63 0.20 0.68 4 D E 0.68 Ac 0.50/0.63 0.85 4.9 4.1 ' S 5 g 1.24 Ac 0.50/0.63 0.50/0.63 1.00 0.26 1.0 7 G 0.14 Ac 0.82 Ac 0.95/0.95 2.50 5.4 ' 8 9. g I 0.27 Ac 0.95/0.95 8 0.4 0.90 1.7 2.0 1 0.31 Ac 0.95/0.95 10 g 0.68 Ac OFF -SITE EXISTING SITE HYDROLOGY TOTAL AREA: 6.27 Acres RATIONAL "cos: 0.2 ON -SITE RUN-OFF: Q2_ 31.7ccfs, Q1000= 13.3 cfs OFF -SITE FLOWS: Q2 DRAINAGE BASINS STATISTICS GROSS PLATTED AREA.: 6.27 Acres GROSS AREA "Cos: 0.53, NET PLATTED AREA: 1.65 Acres NET AREA locos: 0.50 (Per Drainage Criteria) NO ON -SITE DETENTION BASINS: 7 within the net platted area zjr • s 4 I II ; o. 1 1 + t (r • , � I fi` , jj I M M { ! s I El� O ,]eft 1 al ci v 54 N J 0. <fOci a { Ls 0 G 41 I r a, q (Jc%Ii��I�����(���i9 I z ! I TA I s o .fu I I M I ! I I .1• I J I I , I r kle;°��(�I��j�(��► mill I oacl Ial o f e , I I E;; a a� olMoo �!�ooVal 40LN ! •� i I i Nil fil O - < O 54 A. I to , t- I I ! I !