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Home My WebLink AboutPOTTS PUD PRELIMINARY - 6 92 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTI "PRELIMINARY' DRAINAGE IlWESTIGATION (CIA POTTS' - P. U. D. A PROPOSED 26 UNIT MULTI -FAMILY RESIDENTIAL COMPLEX FORT COLLINS, COLORADO Prepared for &RCHOVEC HE ONE 150 East 29th Street Suite 200 Loveland, Colorado 80538 February 3,1992 Project No. PLA-071-92 PREPARED BY: WON3M Engineering Associates 150 East 29th Street, Suite 225 Loveland, Colorado 80538 Telephone: (303) 663-2221 Civil and Environmental Engineering Consultants Client: ARCHITECT uRE ONE By: DRM Project No. PLA-071-92 Date: Jan. 31, 1992 Calculations for Drainage Investigation for POTTS' - P.U.D. located in the SE1/4 of Section 15, Township 7 North, Range 69 West of the 6th P.M., City of Fort Collins, Larimer County, Colorado Total Site Area = 1.669 ± acres The proposed development of the site is to consist of the construction of 26 multi -family residential units to be located in 5 separate structures. EXISTING CONDITIONS - RUNOFF COEFFICIENT From Table 3 - 2 of City Design Criteria manual Rational "C" Factor = 0.20 for Unimproved Areas Therefore, at Existing Condition use "C"an = 0.20 PROPOSED DEVELOPMENT - RUNOFF COEFFICIENT Rational "C" Factor = 0.15 for Lawns and Landscaped Areas It = 0.95 for Roofs, Decks, Patios, etc. " It = 0.95 for Asphalt and Concrete Streets, Drives, and Parking "C"avg : Lawns and Landscaped Areas = 34,050 sq.ft.± = 0.78 acre ± Roofs, Decks, Patios, etc. = 20,077 sq.ft.± = 0.46 acre ± Streets, Drives, and Parking = 18.587 sq.ft.± = 0.43 acre ± Total Site = 72,714 sq.ft.± 1.67 acre ± "C" avg = ((34,050 x 0.15) + (20,077 x 0.95) + (18,587 x 0.95)) - 72,714 = 0.575 Therefore, at Proposed Condition use "C"avg = 0.58 TIME -OF -CONCENTRATION Existing Conditions: Time of Concentration (Overland) = To(min.) = 1.8 [ 1.1 - (Cf x C) ] �L(ft.) _ 3qS(%) Distance, L = 200'± Slope, S = 2' =.175' = 1.1 % Elev. Diff. = 5042 - 5040 = 2' Cf Q 2 Yr. Storm = 1.00 Cf Q 100 Yr. Storm = 1.25 2 Yr. To = 1.87 [1.1 - (1.00 x 0.20)14200 _ 341.1 = 23.05 min. 100 Yr. To = 1.87 [1.1 - (1.25 x 0.20)14200 - 341.1 = 23.33 min. Time of Concentration (Channel): Grassed Swale w/ 140' length ® 0.8%, Tch = 1.55 min. (Refer to attached Fig. 3 - 2) Tc = To + Tch = 23.05 + 1.55 = 24.6 Therefore, at Existing Condition use, To = 30 minutes Page 1 of 4 Client: ARCHITECT uRE ONE Project No. PLA-071-92 By: DRM Date: Jan. 31, 1992 TIME -OF -CONCENTRATION (cont. for Potts'- P.U.D.) Proposed Conditions: Time of Concentration (Roof to Ground) = 5 minutes Time of Concentration (Ground to Street): Tc(min.) = L(ft.) + [Vel. (ft./sec.) x 60 min./sec.] Based upon Velocity for Grassed Swale from Fig. 3 - 2 Vel. = 2.2 ft./sec. Time of Concentration (Street Flow): T(min.) = L(ft.) + [Vel. (ft./sec.) x 60 min./sec.] Based upon Velocity for 2% Gutter Slope from Fig. 3 - 2 Vel. = 2.8 ft./sec. TTotal = TRoof + Tc + Ts Tc=165+[2.2x60]=1.25min. Ts=125+[2.8x60]=0.74min. TTotal = Ts +Tc + Tr Therefore, T = 1.25 + 0.74 + 5.00 = 6.99 min. Tc = (L + 180) + 10 = (340 + 180) + 10 = 11.88 min. USE 10 minutes as Time of Concentration RUNOFF Runoff, Q = C x I x A x Cf Runoff from Site at Existing Conditions:: I2 @ 25 minutes = 1.65 in./hr. Iioo @ 25 minutes = 4.85 in./hr. Qz = 0.20 x 1.65 x 1.67 x 1.00 = 0.55 c.fs. Qioo = 0.20 x 4.85 x 1.67 x 1.25 = 2.02 c.£s. Runoff from Site at Proposed Conditions: I2 @ 10 minutes = 2.50 in./hr. I100 @ 10 minutes = 7.25 in./hr. Q2 = 0.58 x 2.50 x 1.67 x 1.00 = 2.42 c.f.s. Qioo = 0.58 x 7.25 x 1.67 x 1.25 = 8.78 c.f.s. The estimated difference in total runoff volume based upon the 2 and 100 Year Storms is estimated on the following page. Page 2 of 4 DETENTION VOLUME DETERMINATION FOR "RATIONAL METHOD" Time Q100 Prop. Vol. Ca 0100 Q dis. @ 2 Yr. Vol. dis. Vol. Diff. (min.) (c.f.s.) (cu.ft.) (c.f.s.) (cu.ft.) (cu.ft.) 10 8.78 5267 0.55 331 4936 15 7.26 6538 0.55 496 6042 20 6.30 7555 0.55 661 6894 25 5.57 8354 0.55 827 7528 30 5.02 9044 0.55 992 8052 40 4.24 10170 0.55 1323 8848 50 3.63 10897 0.55 1653 9243 60 3.15 11333 0.55 1984 9349 At 02 Existing Q = CIACf = 0.20 x 1.65 x 1.67 x 1.0 = 0.55 At 0100 Proposed Q = CIACf = 0.58 x I x1.67 x 1.25 CACf = 0.58 x 1.67 x 1.25 = 1.21 Therefore, the Detention Volume desired is 9,349 cu. ft. at a release rate of 0.55 c.f.s. This is based upon detaining the difference between the present site conditions with runoff generated by a 2 Year Storm event and the proposed site conditions with runoff generated by a 100 Year Storm event. ARCHITECTURE ONE POTT'S - P.U.D. Proj. No. PLA-071-92 Page 3 of 4 Jan. 31, 1992 DRM Client: ARCHITECTURE ONE Project No. PLA-071-92 By: DRM Date: Jan. 31, 1992 SIZE INLET IN PARKING LOT From Fig. 5-3 with 0.8 depth of flow over grate Q/sq.ft. = 3.95± cfs/sq.ft. with 1.34 sq.ft. of opening Q = 1.34 x 3.95 = 5.29 cfs w/ No. 12 Grate & Frame SIZE PIPE Reduction Factor for sump condition = 80% Q allowable = 0.80 x 5.29 = 4.23 cfs >> 2.42 Therefore, Standard "Area Inlet"is OK Q = 1.486/n A R*2/3 S*1/2 Consider 8" dia. Pipe @ 0.50 % Q = 1.486/0.013 x 0.35 x 0.30 x 0.07 = o.85 cfs>>0.55 Therefore, 8" dia. is OK DETERMINE ORIFICE SIZE Orifice Equation, Q = CA42gh A = Q = C42gh Q = 0.55 c.f.s. (form Page 3) C = 0.65 h=41.50-37.33=4.17ft. A=0.55=[0.65x4(2x32.2x4.17)]= 0.109sq. ft. A=w*2 w=CIA w = �0.109 = 0.33 ft. = 4 inches Therefore, Use 4" x 4" Orifice Opening DETERMINE DETENTION VOLUME High water Elevation = 41.50 Area @ 39.50 = 100 sq.ft. Area @ 41.50 = 11,000 sq.ft. Inlet Grate Elevation = 39.50 Area @ 40.50 = 3,800 sq.ft. Vol. _ [(100 + 3900) 21 + [(3900 + 11000) + 2 ] = 9,450 cu. ft.> 9,350 OK Page 4 of 4 DRAINAGE CRITERIA MANUAL RUNOFF C 50 30 I— 20 Z W U cc W o. 10 Z w 0. O 5 N w oyc 3 O v 2 Cr w I- 3 1 �■■■■� IIII / I /1DWANE �M■ ►A I ,�■ I I I AMNON� �� Imam �� IEmsMEN I ■� �WA- MMII� �� /�=/IMFA F �AWA MM NO INNONNIN MMO �jMWAM EVIM III■■�I�� 2 .3 .5 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 8 FLOOD CONTROL DISTRICT l M 0.7 f- w 0.6 z 0.5 Cr > 0.4 0 x a 0.3 w 0 ? 0.2 0 z 0 a 0.1 0.( EXAMPLE > 3 5 p 4 I 2 FLOW INTO INLET PER SO. FT. OF OPEN AREA (CFS/FT2) Figure 5-3 CAPACITY OF GRATED INLET IN SUMP (From: Wright -McLaughlin Engineers,1969) MAY 1984 5-11 DESIGN CRITERIA Engineering Associates February 3,1992 Project No. PLA-071-92 Mr. John Freeman, Architect ARCHITECTURE ONE 150 East 29th Street Suite 200 Loveland, Colorado 80538 Dear Mr. Freeman, The enclosed report represents the results of the Preliminary Drainage Investigation for POTTS' - P. U. D., a proposed multi -family residential complex to be located on a 1.7 ± acre parcel at the Southwest corner of the Matador Apartments - Phase IV in the City of Fort Collins, Larimer County, Colorado. This investigation was based upon the proposed site development plan; proposed site grading plan; on -site observations; and available topographic information. The investigation was performed in accordance with the criteria established in the City of Fort Collins "Storm Drainage Design Criteria and Construction Specification Standards" manual. Thank you for the opportunity to be of service to you. If you should have any questions, please feel free to contact this office. Respect f y Submitted, Dennis R. Messner, P.E. MESSNER Engineering Associates DRWmkm Enclosures Civil and Environmental Engineering Consultants 150 E. 29th Street, Suite 225 Loveland, Colorado 80538 Telephone: (303) 663-2221 TABLE OF CONTENTS Letter of Transmittal Table of Contents Scope Site Description Existing Conditions Proposed Development Erosion Control Measures Conclusions and Recommendations EXHIBITS Vicinity Map Existing Conditions Exhibit Grading & Drainage Exhibit Landscape Plan/Erosion Control Exhibit Calculations ii SCOPE The following report represents the results of a preliminary drainage investigation for a proposed 26 unit multi -family residential complex to be located on a 1.67± acre parcel of land situated in the Southeast Quarter of Section 15, Township 7 North, Range 69 West of the 6th P.M., Larimer County, Colorado. The site is located at the Southwest corner of the "Matador Apartments - Phase IV" in the City of Fort Collins.The investigation was performed for ARCHITECTURE ONE. The purpose of this investigation is to determine the effects of the proposed development on the area's existing drainage conditions and to determine the improvements, if any, and the appropriate sizing for proposed improvements so that it may be incorporated with the construction of the project. The conclusions and recommendations presented in this report are based upon the proposed site development plan; proposed site development construction plans; on -site observations; and the available topographic information. The analysis was performed in accordance with the City of Fort Collins "Storm Drainage Design Criteria and Construction Standards" manual. SITE DESCRIPITION The site is irregular in shape and contains approximately 1.699 acres. The site's East-West dimension varies but is considered to average approximately 175 feet. Its North -South dimension is approximately 450 feet. The site abuts the easterly right-of-way of the Larimer County Canal #2. The site is located approximately 350 feet south of West Elizabeth Street and 700 feet west of City Park Avenue. The site is located In the SPRING CREEK DRAINAGE BASIN. EXISTING CONDITIONS The site is presently vacant and undeveloped. The ground cover consists of native pasture grasses and a few volunteer trees. The ground slopes toward the northeast and is relatively flat with grades ranging from 0.75% to 1.5%. The "Soil Survey For The Larimer County Area" prepared by the U.S.D.A., Soil Conservation Service, indicates that the upper layer soils are a sandy clay loam. "The Survey" indicates that the soils have a slow to moderate runoff potential and have slight to moderate wind and water erosion potential. The area surrounding the site is virtually fully developed. As previously stated, the Larimer County Canal #2 forms the western boundary of the site. The area to the west of the canal is a single-family residential subdivision known as Fairview. To the north of the site are a Taco Bell restaurant and a Diamond Shamrock convienence store. The areas immediately adjacent to the site on the north consist of parking lots for the Taco Bell and a C.B. & Potts restaurants. The area adjacent to the site on the east consists of the Matador Apartment complex. The site does not receive runoff from the surrounding properties. The runoff from the area to the west is intercepeted by the Larimer County Canal #2. Runoff from the area to the north flows to the north and east away from the site. Runoff from the area to the east flows to the north and east away from the site. Runoff from the site flows overland to the C.B. & Potts' parking lot. The flow is detained within this parking lot and discharged through a controlled release into the Diamond Shamrock drainage system. This eventually discharges into a 15" dia. storm drain that flows east in West Elizabeth Street. 1 PROPOSED DEVEL. OMENT The proposed development of the site is to consist of constructing 26 multi -family residential units along with the associated access drives and parking. The runoff generated on the major portion of the site is to be routed overland to the access drive. The drive has been preliminarily designed to be graded to a low point situated approximately in the middle of the site. A storm drain inlet is to be constructed at this point in order to intercept and collect the runoff. An orifice plate is to be placed over the inlet end of the pipe outfalling from the storm drain inlet. The orifice plate will act as a control device to limit the rate of flow discharging from the site. The runoff will be detained and will pond in the access drive and parking areas due to the restricted release rate. A 15" dia. storm drain pipe is to be installed to route the flow to the C. B. & Potts' parking lot. The minor area in the northeast corner of the site that is not routed to the internal detention area will flow overland into the C. B. & Potts' parking lot. This routing will retain the original drainage pattern and will provide for drainage of the proposed use. EROSION CONTROL MEASURES Erosion control considerations have been made based upon the short term, i.e., during construction activities and the long term, through the life of the facility. The long term measures that are to be incorporated into the project in order to reduce erosion are the proposed methods and materials to be used to provide a surface covering for the parking areas, walkways, driveways and the landscaped open areas. The structures and hard surfaced areas will provide a covering to deter erosion. The landscaping to be established will be a combination of plantings and ground covers to deter erosion. (Please refer to the proposed "Landscaping Plan") The short term erosion control method to be incorporated into the construction requirements for the project is the placing of "Curb Inlet Filter Gravel" at the proposed storm drain inlet to be constructed onsite. It is not considered as necessary to provide any wind erosion measures due to the protected nature of the site. The schedule for construction activities is anticipated to be: April 15 - June 30, perform earthwork grading operations, install utilities and construct access drive; May 1 - August 15 construct initial 6 unit structure; July 1 - April 1, 1993 construct remaining structures; July 15 - April 15, 1993 instal landscaping in conjuntion with completion of each structure. This schedule is proposed as the conservative time line with the anticipation that actual construction will proceed on a faster schedule. In any case the site will be "open" and subject to water caused erosion for an extremely short period of time. 2 CONCLUSIONS AN , RECOMMENDATIONS 1. The proposed development will retain the existing drainage patterns. 2. The site is located in the SPRING CREEK DRAINAGE BASIN. The site is not located within the floodway or flood plain. 3. All development is to be performed in accordance with City of Fort Collins Standards and Specifications. 4. Onsite detention of stormwater is to be provided. The runoff volume difference between the existing and proposed conditions is estimated to be 2,656 cu. ft. when based upon the difference between the runoff from a 2 Year Storm with the site considered at the existing condition and the runoff from a 100 Year Storm with the site considered at the proposed conditions. Therefore, a detention volume of approximately 9,350 cu. ft. has been designed to be provided onsite and the flow is to be released at a rate of 0.55 c.f.s. 5. The City of Fort Collins Standards for temporary erosion control measures are to be incorporated with the construction activities. 3 EXHI :ITS VICINITY MAP Tom• _ _/NE GRr E! I '• __r ,. .,•• I'• t° '. i i�.n` :I t 5022J r 1. SC r r❑�j R ,❑ r e,sl PU 1 �99. 1 l re . YFeWiI� �•r., — — - yi �Ll dounlain \'iiw i i ��% i, 1 ..' l i�ve l�� 4985 � _i 'Sch431 •9�iW�`.—= r ; C La',Porte Ave \ �, 15058'•.�� •,�l _ LL �L &h'1 �P ❑ A Puadre Grandvee ' _:'r' s' rMOUNTA`Id`J I \2 EIr; '.. r Aigh h ii +�A LJ500 . ` - - I Munici z,� • -per':>, Ei Sch ( i �. — 5' = oo-- LJI `j 7I Golf Course • Skeldon, . �...... y. 1. IS.; / •' 5069- . ' Lp 6 - _ ..I! Trailer \�`i �I Z J I� } Alzl Park E �j \ �• ' = . - ra�o ,. Eirl_ ❑� oil �. t fir:. �-ST Erg 5 •'• •��• oI= ti•L• ^'I z.�' ...R.. /UNR'ERSITY 4 n � r Be FHig _r -�•-r__/�, ��. OSP OTi ,_�.�.: •�• 3�I� ��r._ _ L...1• R �0 1 5065I c� 056 % 5028 �� . - n 15. Vicinty Map for POWs' - P. U. D. located in SE 1/4 Section 15, Township 7 North, Range 69 West of the 6th P3L Fort Collins, Colorado No Text