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HomeMy WebLinkAboutDrainage Reports - 09/20/2010CORNED CONSULTING COMPANY P.b. box 646 fORT c0111 s, CdoRxb 80522 P�"*: (303) 482.6650 am MANAgEMENT/ENGINEERiNG MASTER STORM DRAINAGE AND DETENTION PLAN FOR EVERGREEN PARK Fort Collins, Colorado ' Prepared by CORNELL CONSULTING COMPANY 214 ?Vest Mountain Avenue Fort Collins, Colorado 4 CORNET( CONSU)TINq COMPANY Robo\646lorarcollms,cohf?kk)W5220KYE:(303)482.66k! -- MANAfjEMENI/ENCj NEEAiNq TABLE OF CONTENTS Title Sheet i Table of Contents Report 1-16 Detailed Analysis , Hydrograph"Routing to Size Sag Culvert 17-25 Dry Creek Flood Plain Profile 26-27 Appendix Requirements for Drainage Area 1 28-32 t Requirement's for 'Drainage Areas 1 $ 2 33-37 Requirements -for Drainage -Area 3 38-41 Requirements for.Drainage.Area 4 42-45 Requirements for Drainage Area 6 46-47. Requirements for Drainage Areas 5 $ 6 48-51 Attachment Aerial Photograph with Location of Proposed Detention Facilities '�' COR**U CONSU INCH COMPANY POIXA646 for collw%coloaodo80522 fly (303)482-6650,= EVERGREEN PARK NIIASTER DRAINAGE AND DETENTION PLAN I. Background Evergreen Park -is a multi -zoned development located in the northeastern part of the City of Fort Collins, Colorado. The property lies in Section 1, T7N, R691V and is bounded on the west by. U.S. Highway 287, on the north by Willox Lane and on the east by Lemay Avenue. Lake Canal flows west to east through the Section and is the southern boundary for apart of Evergreen Park. The general slope.6T the land is from northwest to southeast toward Lake'Canal at one-half to one percent. All of Evergreen Vark was agricultural -type land prior to development for residential, industrial and commercial uses. Filings 1, 2.and 3 of Evergreen Park are recorded developments within the overall project. Drainage studies were made for those filings, and were approved by the City of Fort Collins prior to acceptance of the final plats. Since the first filing was approved in 1974, the storm drainage criteria and policies of the city have been upgraded in keeping with federal regula- tions and with the "state of the art." Current city requirements are based largely on the Urban Drainage and Flood Control District's "Urban Storm Drainage Criteria Manual' (U.S.D.C.M.) and the master drainage and detention plan reported here is compatible with that ' publication. Storm runoff from the first three filings affect the remaining property within Evergreen Park which is z currently being designed and platted. In order to conform to current requirements for drainage facilities on Filing 4 (now in the final design and platting stages) and on future filings, it was necessary to up- t grade the drainage criteria for previously studied areas, and to incorporate platted and un-platted prop- erty in an overall plan to control peak storm discharges. II. Scope of Work For this investigation, drainage basins were defined from topographic information and field investi- gation. Physical characteristics of the drainage basins such as slope, natural ground cover, percent of impervious surface area and.flow paths were utilized to determine peak storm discharges from each basin using the Rational Method of Storm Runoff Determination. { Storm runoff detention requirements were calculated using the Cumulative Runoff Method as proposed in the ,) Urban Drainage District's (UDD) Urban Storm Drainage Criteria Manual,.and were based upon storage of the 100- year storm discharge;after`total development with a release rate eoual'ta the two-year historical storm discharge. Special attentioji was paid to controlling the 100 year peak flood event* throughout the project '- in order to Drevent-or minimize damage as a result of passage of major storms through the property. The master drainage plan is inter_ded to be an over- a all view of the major drainage system through the project, 7 and individual filings should be designed to accommodate a the master plan for drainage. The grading of streets, lots and detention areas and the sizing of drainage :., facilities for the initial, or on -site, drainage system_ for the fourth and future filings will be submitted separately with the improvement plans for each filing. 3 Hydrologic Investigation For purposes of this study, six (6) drainage basins have been defined as contributing storm runoff to Evergreen Park (see Figure 1). The Dry Creek water- shed upstream contributing storm runoff to the property is discussed in a separate section later in this report. Rainfall Intensity -Frequency Curves for the peak storm events anticipated for the study area were pro- vided by the City of Fart Collins and are included as Figure 2- of this reoor.t: The'100-year and 2-year storm rainfalls were used in this study in order to determine detention. requirements and to allow hydraulic design.to. Prot ect the•public from damage during passage of the maj.or.,':l00-year,, flood event. The Rational Formula for Storm Runoff Determina- tion is: Q = CiA, where: Q = Peak rate of runoff in cubic feet per second. C = Coefficient of runoff, or ratio of storm runoff rate to rainfall intensity. j.•= Avera;ge'rainfall intensity, in inches Per hour, for a storm duration equal to the time of.concentration. A =' Water'shed area in -acres. Several assumptions are made when applying the Rational Formula, but the method is an adequate estimate of peak storm runoff. .The "Time of Concentration (TC)" is the time for storm water to flow from the most remote part of the drainage area to the point of interest. Time of Concen- tration is estimated from Xirpich's Formula (Curves) for the overland flow in the upper reaches of the basin plus the flow time to the point of interest once initial IA 4 MR, runoff becomes concentrated in a street gutter, storm sewer, drainage channel or natural streambed. The concentrated flow time is estimated from the average velocity of flow as given by 14anning's Formula for the hydraulic conditions of the drainage facilities. carrying the runoff. An average rainfall rate (i) of 1 T d t r. d a corresponding duration (equa to C) is e e mine from the Rainfall Intensity-Freouency'Curves to t the rainfall which will yield Deak storm represen discharge for any frequency event. The runoff coefficient "C" varies with numerous factors such as infiltration, interception, detention storage, -evaporation, retention, flow routing, and percent of im4ervious.Iarea. The runoff coefficients chosen for.each basin 'in this study were composite values based•,on area -weighted percentages of different . types of surface, or land -use, within the drainage area. The range of suggested runoff coefficients for each land use are provided in the U.S.D.C.M. at Table 3-1. Median values were chosen.for the coefficient to represent a particular land -use, and the weighted co- eff•ic'ient calculations are included in the data sheets for each drainage area studied (see Appendix). The U.S.,D.C.M. recognizes a need for adjustment of the runoff coefficient for.major, or infrequent storms, to account for higher rainfall intensity. This frequency factor, "Cf," is included in the Rational Formula as Q = CiACf. For the 100-year storms investi- fated for Evergreen Park, "Cf" is equal to 1.25. That represents a 25 percent increase in estimated storm runoff above what the Rational Formula would shore for' normal intensity and infiltration conditions. ■ m IV. Hydraulics Once the design storm runoff quantities are estimated, the detention storage and other drainage facility requirements are determined. The "Cumulative. Runoff Method" of determining runoff storage require ments was.appiied'to evaluate the existing and proposed drainage control lakes, or detention ponds, for Evergreen mark. 'The utilisation of this method generally leads to lar,g.e..storage requirements and a conservative design. As -covered in the design manual, there are several ways in which to temporarily slow- down, or store, storm runoff. On -stream storage,.with lakes, channels and parking -lots providing the majority of the storagq!requirements, is the basis upon which this drainage plan was derived. The 'Cumulative Runoff Method" provides a graph of storm runoff volume versus time for storm water entering and' leaving the particular detention pond. According to current criteria, storage required in a drainage area is to.accommodate the 100-year storm runoff after full development of the basin occurs, while'teleasi•ng the;p6nded water at a rate equal to the two (2)-year historical., or undeveloped, storm discharge amount.. •It could be argued that a two-year release rate is too,conservative; and that the 100- year historical discharge should be the release rate from the property during a 100-year event. That way the excess runoff volume caused by the particular development would be the required storage volume. The greater the storage provided upstream, the less the release rate and the smaller the drainage facilities downstream. For this project, it was determined that the advantages realized by maximizing storage facilities--releasin only the two-year historical runoff rate --and thereby minimizing the drainage facility requirements downstream outweigh the disadvantages. Therefore, this plan incorporates detention facilities to store all major storm runoff and release the 2-year historical store runoff rate from the property: Under other circumstances, a release rate higher than for the two-year historical runoff --up to the 100-year historical runoff. might be more reasonable and beneficial. In the appendiX. are..charts.and calculations for the .design of detention facilities using the "Cumula- tive Runoff Method," for the application of ":annino's Equation to open -channel flow, and for hydraulic analysis of outlet control structures for the detention r. ponds. V. Discussion of Study Procedures The Master Drainage Plan was developed by working with progressive larger drainage areas from the up- stream end of the basin. A detention pond (Lake No. 1) was designed for Drainage :4rea 1 during Filing 1 planning and,design'.,(see Figure 1 for location). ` Storage requirement's were computed using the 20-year storm runoff with development and the 2-year historical storm as a release rate. The.drainage study for Filing €� 1 also proposed a second lake at the southeast corner of Conifer Street and Redwood Street and a storm sewer from that intersection to the lake. Detailed design was.not included for those facilities. Storm sewer systems were also designed in Filing 1 to collect storm runoff. One system was designed to �4 drain runoff from the northerly part of Filing 1 under Blue Spruce Drive into Lake 1, and the other was -laid out to drain runoff from the southerly part of Filing I 7 Ev"'.3" to and under Conifer Street to the south.. Single catch - basins were assumed to accept seven (7) cubic feet per second of storm runoff, and the storm sewer system was sized using Manning's Equation to carry, the total flow from contributing. catch basins. A 25=food wide "V"-shaped drainage ditch within a 25-foot drainage easement was designed to carry over- flow from Lake 1 to the northwest corner of Conifer and Redwood Streets, and the outlet structure for Lake 1 was designed to pass 10 c.f.s. through a Broad Crested Weir 1.7 feet wide and 1.8 feet deep. As shown in the.appendix, the two-year historical storm runoff rate for Drainage Area 1 was determined by this office to:be 20'c.f.s.'from Drainage Area 1, and 20 c.f.s. is the allowable release rate from the basin. Utilizing the Cumulative Runoff Method, the required runoff storage is 13 acre-feet. The active detention storage volume of Lake 1, according to the design for the outlet control (release) structure during Filing 1, was 8.5 acre feet. By lowering the invert elevation of the weir, structure' from 4,966.0 (as proposed) to 4,964.5 feet., the dimensions of the Broad Crested Weir structure required to actively store 13 acre-feet while releasing 20 c.f.s. becomes 1.7 feet wide and 2.65 feet deep. This design allows the grading plan for Lake 1 to remain as designe& for Filing 1, except. for lowering the outlet invert elevation 1.5 feet and raising the bottom elevation of the lake from 4,956.0 to 4;961.0 feet. The bottom elevation was raised since the water table has already been reached at 4,961.0 and the additional depth is not necessary for, active detention. The drainage channel proposed in Filing 1 to handle over -flow from Lake 1 to the storm sewer at the 0 intersection of Conifer and Redwood Streets was a "Vee" shaped open ditch. That type of facility has been designed by this office to fit the vertical restraints of the outlet structure, the natural ground, and the existing storm sewer in Redwood Street.A profile and typical cross-section of the drainage channel appears in the Appendix. Drainage Areas 1 and 2 combined contain 211 acres and are contributary. to -Lake 2 (see Figure 1 for loca- tion). The two-year historic storm discharge was estimated by this office to be 29 c.f.s. from the combined drainage area. The required storage was determined to be 22.3 acre-feet using the Cumulative Runoff Method Tor the 211 acre basin. Lake 1 provides 13.0acre-feet of active storage, leaving 9.3 acre-feet to be stored. Lakes 2 and 3 wer.e designed to store storm runoff from Filing 2 and were platted as Tracts A and B respectively. Tract A had a surface area of approxi- mately 4.0 acres, but the encroachment of Filing 4 into the southern 50 feet of Tract A reduces the surface area of Lakg 2 to 3.4 acres. The part of Lake 2, or Tract A bf Filing 2, overlapped by Filing 4 will be abandoned.-. The lakes as designed for Filing 2 actually have very small active detention storage capacities, since' there are no outlet structures. Apparently, an assumption was made that the lakes were empty when the majoY storm runoff began, and most of the runoff volume was stored before ponding reached the berm over- flow elevation. That approach is not acceptable according to the Cumulative Runoff Method of detention. storage requirements. E This office has redesigned the Lake '- grading and outlet structure to actively store 9.3 acre-feet and release 29 c.f.s., according to the concept of storing the 100-year "fully developed" storm runoff and releasing the historic two-year storm runoff rate (see Appendix). Again a "Vee"-shaped open channel was designed to pass'the overflow from Lake 2 southerly through Filing' 4 to Lake. 5. This open ditch and 25- foot easement has been centered on the back line of the lots fronting Redwood 'Street. Utilities installation should be avoided in the drainage easement where possible, although the infre- quent flows in the ditch will be at low velocity (less than 2 feet per second). The two internal street crossings of the ditch were determined to be feasible using condrete box culverts under the streets at the channel location. The detailed design of the street and utility crossings are a Dart of the improvement plans for Filing.4'. The sanitary sewer Crossings under the open ditch (channel) were investigated also, and fpund to .be a minimum'of 2.5 feet below the ditch invert.' Lake 3 was inadequately designed during the 2nd Filing'of Evergreen Park, ;and made a part of the Replat of the 2nd Filing as Tract B.'..The 3rd Filing of Ever- green Park abandoned Track B of ,the 2nd Filing and replatted a similar area for detention as Tract A in the 3rd Filing Plat (see Figure 1). No additional design for the revised detention area layout could be located by this office. The Lake 3 detention area does not effect the 4th Filing or future filings, of Evergreen Park, and it was officially dedicated to the public on the 3rd Filing Plat. For these reasons, the developer(s) of 10 P. ff � the 4th or later Filings does not intend to make improvements to Lake #3 to provide adequate active detention according to current criteria. However, this office has determined improvements that could be made to Lake 3, in order to provide a design which would allow adequate storage, and in order to be consistent with the -overall master drainage plan for Evergreen Park. The design information relative to Lake 3 follows in the Appendix. Lakes 4 and 5 are being platted as Tracts A and B respectively on the 4th Filing of Evergreen Park by this office (see•Figure 1 for locations). Lake 4 has been designed to store the 100-year developed storm runoff,ftom Drainage Area 4, or the easterly portion of-the.4th Filing and some of the open area south of Filing Three. The two-year historic storm discharge was estimated to be 4.9 c.f.s., and that release rate plotte d against the 100-year developed storm runoff volume versus time on the "Cumulative Runoff Method" graph yields a required storage of 1.9 acre-feet (see Appendix). Again, a wier-overflow structure has been designed to contain.the runoff in the 1.25 acre detention area (Lake 4), and a minimum of grading will be required to direct the release storm water to the 65 foot Dr*'ainage and Utility Ease- ment southerly of Lake 3. Lake 5 is located at the extreme southend of the 4th Filing, and is bounded on the east by Lake Canal and on -the west by Redwood Street (see Figure 1). This detention pond receives (in some manner) and releases storm runoff from Drainage Areas 1, 2, 5 and- 6. It acts in unison with Lake 6, westerly of Redwood Street, to actively detain the 100-year developed storm runoff from Drainage Areas 5 and 6 combined. 11 -- Additionally, the release rate of discharge (29 c.f.s.) from Lake 2, which stores runoff from Drainage Areas 1 and 2 combined, enters Lake 5 via the drainage channel through Filing 4. The outlet structure from Lakes 5. and 6 has been designed to.release that 29 c.f.s. plus the two-year historic stormrunofffrom Drainage Areas 5 and 6 combined (14.c.f.s.) for a total release rate of 43 c.f.s. The two detention areas (LakesS and 6) are joined by a 36 inch diameter reinforced concrete culvert (R.C.P.) under Redwood Street to allow flow between the two lakes in order to fill and empty them simul- taneously. Thg two-year historic storm runoff of 43 c.f.s. wili`be released in a sag culvert from the east bank o£ Lake 5 under Lake Canal into a very large, existing detention area along the old Dry Creek stream - bed. The City of Fort Collins staff has dictated to this office that the released storm runoff from the contributary area within Evergreen Park to the south end of the 4th Filing be released into the Dry Creek streambed downstream of Lake Canal, rather than the canal itself, to prevent flooding or contamination Of the canal.'. The very large"existing detention area along Dry Creek downstream of Lake Canal is ideal for . receiving the released storm runoff. The detailed design for the sag culvert release structure is included in the grading and detention sheets in the 4th Filing utility plans. Drainage Areas 5 and 6 combined consist of 87 acres of property to be developed for industrial and residential uses. The Qranh of the "Cumulative Runoff Method" for Drainage Areas 5 and 6 show a storage requirement of 12.6 acre-feet when the 14 c.f.s. 12 M1I release rate is plotted a,-ainst the 100-year developed storm runoff volume over time. Drainage Area No. 6 contains 34 acres of land in Filing One to be developed as commercial and industrial property. The previously mentioned storm sewer system designed in the 1st Filing to collect storm runoff from the southerly portion (which is Drainage Area No. 6) and release it'southerly of Conifer Street has a capacity of approximately,50 c.f.s. As Conifer Street was designed to fall easterly from College to Redwood Street, any storm runoff in excess of 50 c.f.s. will flow to the intersection of Redwood Street. For this reason, a'graph of the.100-year developed storm runoff over time for"Drainage Area 6 was plotted against a 50 c.f.s. release rate (see Appendix), showing that 2.3 acre-feet o'f detention storage should be provided with parking areas, roof -tops, or otherwise in Drainage Area No. 6 to ensure a maximum storm runoff from that area of.'50 c.f.s. A "Vee" type ditch has been designed by this office to carry the,.50 c.f.s. release rate from the south side p•f Conifet'Street to Lake 6.(see Appendix for details). ;An existing 6" gas main was located horizontally and vertically in the vicinity of the drainage ditch crossing by this office. Its elevation relative to the ditch -flow -line necessitates utilization of a sag culvert to pass the storm runoff under the gas main to provide a one foot minimum clearance between the culvert and gas main. The design of that sag culvert is included in the Appendix. Recalling that the required storage for detaining, the 100-year developed storm runoff from Drainage Areas 5 and 6 is 12.6 acre-feet and that 2.3 acre-feet is to be provided within Drainage Area 6, the required 13 active detention storage that must be provided in Lakes . 5 and 6 (acting together) is 10.3 acre-fee.t. The determination of the active detention depth and corresponding lake surface area is complicated by the sag culvert release facility and Dry Creek deten- tion area downstream of Lake Canal. Preliminarily, 30 and 36 inch R.C.•P.'s were investigated using the criteria outlined at Pa.-e'184_ of the Handbook of Concrete Pipe Hydraulios:by the Portland Cement Association. The head "H' required to pass 43 c.f.s. in the sag culvert under Lake Canal was determined to be 1.43 feet for the 36 inch diameter R.C.P. and 3.20 feet for the 30 inch diameter R.C.P. (with projecting - end type ent.rance). The to;Ll.water depth "TW" was determined by rating the channel of Dry Creek downstream of the outlet from the'sag culvert. With an invert eleva- tion of 4953.5 and'a normal depth of flow of 1.3 feet, the tail water depth was found to be 4954.8 feet, making the lake water surface elevation 4956.23 feet for a- 36 inch culvert and 4958.0 feet for a 30 inch culvert. In order :to evaluate the preliminary design of the sag culvert, it was necessary to look at the storm runoff volumes of all areas"contributary to the deten- tion area existing on Dry Creek downstream of Lake Canal on a time basis. This was done to find the relationship of the storm runoff versus storage in the Dry Creek detention area as a check against the preliminary determination tail water depth "TW" in the sag culvert design. A stage -storage curve was derived for the deten- tion area on Dry Creek., and hydrographs were drawn for each of the contributing Drainage Areas and routed into 14 VI. the Dry Creek detention area. This analysis showed that the maximum tail water elevation will be 4954.9 feet after storm runoff has ceased, while the maximum tail water plus head required to pass• 43 c.f..s. through the sag culvert (30 inch R.C.P.) will be 4957.6 feet at one hour after the beginning of storm runoff. The tail water elevation at the time of maximum discharge will be 4954.2 feet. 'Therefore.,'an active detention depth of 3.4 feet is provided•in'using a 30 inch diameter R.C.P. for the sag cuIvert.under Lake Canal. With 10.3 acre-feet of detention storage required, a total lake surface area. (measured. at the mean elevation of the - active detention depth) of 3.03 acres. The average' Lake 5 surfa:ce area is 0.9 acres at the mean actiye'detention depth (taken at 55.5 contour). Therefore, an average surface area for detention in Lake 6 of (3.03 - '0.90 =. 2.13 acres) must be provided in the industrial property westerly of Redwood Street. Conclusion The Master Drainage Plan as outlined in this report will allow for;'control of major (and minor) storms affecting:Evergreen,Park'. The particular drain- age facilities within the Fourth Filing of Evergreen Park have been designed in detail -and included in the Utility Plans submitted with the final plat for that subdivision. r i r + I � I � I Y � I AREA al I . I I AREA 's2 I • � I AREA *3 LAKE L. I I AREA'FG I r I LAKE'�g I ' LAKE 1�—�---� AREA"4 LAKE "4 • AREA 1*5 1 1 / LAK6'�'6 1 EVERGREEN PARK LAYOUT OF DRAINAGE AREAS SCALE: 1" = 1000' Im ® DETENTION POND u FIGURE I 'ifto 4~ CITY OF FORT COLLINS, COLORADO RAINFALL INTENSITY DURATION CURVE NOVEMBER, 1975 BASED ON DATA AND PROCEDURES FROM NOAA ATLAS 2 — PRECIPITATION - FREQJENCY ATLAS OF THE WESTERN UNITED ST;, VOLUME M - COLORADO Z 5 MA Y err 1Ajrr-tJ-'- Lu pi CL _471 V) LLJ z z 0 CL T 4 EA 120 30 60 90 50 It? rn CITY OF FORT COLLINS, COLORADO RAINFALL INTENSITY DURATION CURVE NOVEMBER, 1975 BASED ON DATA AND PROCEDURES FROM NOAA ATLAS 2 — PRECIPITATION - FREQJENCY ATLAS OF THE WESTERN UNITED ST;, VOLUME M - COLORADO Z 5 MA Y err 1Ajrr-tJ-'- Lu pi CL _471 V) LLJ z z 0 CL T 4 EA 120 30 60 90 50 It? rn 17 The following detailed calculations concern the sag culvert analysis and design for release of stored storm runoff under Lake Canal from Lakes 5 and 6. Drainage Pattern in Evergreen Park Area #1 drains to Pond.#1 Pond #1 $ Area #2 drain to Pond #2 Pond #2 & Area #5, #6' drain to.Pond #5 Pond #5 & Area.#7 drain to Dty Creek Lake To determine -the size of release structure needed from ;pond #5 a 100-y.ear storm was routed through the watershed using straight line hydrographs' derived from the Rational t,ethod peak. First the hydrographs were developed: TC Duration Qp Qp Drainage H L Developed I of Inflow "C" Inflow Outflow Area Area (ac) (ft) (ft) (in/hr) 2.67 x (5) (cfs) (cfs) 1 113 15 3 2'0 0 2A 4.7 64 .40 212 20 2 98 22 3500• 2 4.8 61 .40 188 29 6 34 5 2204 12 6.65 32 .40 90 SO 5 53 12 2800 12 6.65 32 .40 141 43 7 37 6 1500 36 3.'75 ' 96 .25 35 20 Other input is flow time between ponds direction of flow a 1+2 2 5 6 *5 5 DCL time in minutes 17 13 12 10 18 ItJ L`Low PEA..[ ZIZ Gf6 i& Z4 m�...:. �I d a d I i Zo cFs @ 6z m . TInnE GO�+"PogITE y" c7-5 18S cis. I � @ z3.�n,,�. a.eEs�.-�zz .. 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Z-'7 3�- 6o Z4 57 57. $ZOQBO / . 68 3, 15 Go---.Ar� 57 41 Iosago Z.4-3' ' S,SS 9&-886 ' 90 4 I o 9'7 170o ZZ.31 Z 7, as �'oT4L Iwitrt-oU1 27.$9 W, Stage -storage curve for Dry Creek Lake Elev. Area Area A z n n+ 1) Vol. Accumulated Vol. ft2 Ac l/ 3 J 49.5 0 0 0.00 0.05 0 50 12900 0.30 0.71 0.90 0.05 51 74000 1,70 2.90 3.1 . 8 0.95 52 215100 4.94 5'.83 5_88 4.13 53 299500 6.88 7.15 -16 10.01 54 324000 7.44 7.67 70 17.17 ss 34400.0 7.90 8.19 8.19 24.84 S6 370000 8.49 33.03 bj i w w L A° to zo 50 q� Retained Vol. (Ac. ft.) Stage -Storage Curve for Dry Creek Lake Dry Creek Lake therefore reaches an elevation of 55.37 during - the 100 year flood. The following table shows calculations to determine maximum WS elevation of Pond #5 8 To achieve 10.3,'acre-ft of detention as called for in the master plan the detention area must be 3.03 acres. Time Q Ac. voi in dry creek pond pg ury Creek Elev. iw see below n" see pg below rwiu ttZ) waLar surface RSV $ HW 0 0 0 49'.,5 83.5 0.0 53.5 36 22 1.27 51r1f 54.'2 0.9 55.1 60 43 3.15 51.7 54.4 3.4 57.8 96 41 5.58 .52.3 54.4 3.0 57.4 86 0 .27.89 55.4 55.4 0.0 55.4 V = 1. 49. R '301 Q = VA S = 0.0025 Sh = 0.050 n = 0.030 - grasslined Depth A P R V Q 0 ,1; 0 0 0 1. 34 6.80 .0500 0.34 0.12 2 1.36 13.60 .1000 0.54 0.73 .3 3-06 20-40 .1500 0.70 2.1 .4 5.44 27.20' .2000 0.85 4.6' .5 8.50 34.00 .2500 0.99 8.4 .6 11.94 34.21 .3490 1.23 14.7 .7 15.46 34.41 .4493 1.46 221.6 .8 19.06 34.62 SSOS 1.67 31.8 .9 22.74 34.82 .6531 1.87 42.5. 22 777_.7 Use the closed conduit equation to determine head loss in the snag culvert. l H=C0:0252 Kc + 3 Kb + 1 + .185 (n2 L.4I 1 �2U4 - entrance loss i loss in 3, bends outlet loss —I loss from pipe friction KC = 0.46,'Kb 0.15, L 100' for concrete pipe n = .013 for CMP n.=..027 cone ' NP Q 1 30" 0 1. 36" 0 I 30" 0 1 36" 0 22 .88 .40 1.84 .76 43 3.38 1.51 .7.02 2.89 41 3.07 1.38 6.38 2.63 Recommendations: - Use 30" reinforced concrete pipe for sag culvert in- stalled as skown on_next three pages. �.1 a b \tea.. Dllc rc �L..OPE- ,Q Q� ! OITGH i / GoN'ST �o�� EVSE !ca 45' HoeIL. MAE duo ¢T/ i \ j GTt O/.i "cn.7T 7. . GLjL_\,/E�T Pl_/��1 19 0 vS,o IULET tr_Jv Doom BP�TOM r75.5- 30" vErz•r. ESEuo ///... LDKE GAUdL 57.10_ 57.2 GUTOGG WhL.I_ "� I L1oTE : I.J STp-. L.l.,, 6Ln.TE a•T l30'7'H Ei--1D�j Ot= C LJ L.VE2T r- doE OF fo 13de'S Q FSO.G. T3oTH OUTLET 53. g 48.5 !�'� 30• vE.er 0��v i !c"CO Li . E1Jcv.3 r-i'1- A5° Noe�z. P�Euv 8 SEGT"I © �-! ,a,_ �. .5 ToP OF airGH 15 , tC -��GfiO1.J 6-g 1--aoTES 1. TZEIJGL.i To 6E BAC+G FIB-�..Ep STI�UD4iZp Pf�OCTpE , TW.o SET I.r-JTO LJ���SY�Je66� E,c.LYN O F--� i3 �rH SIDES O'er -ii-1E T(LTc.N GK. a 26 8 The following discussion concerns the setting of minimum floor elevations in the flood plain of Dry Creek (southerly most 7 lots) for the Fourth Filing of Evergreen Park. The grading plan for the Fourth Filing ('see Utility Plans) shows . that the required protection has been provided. This determination is based largely on a "worst -case" x analysis of the conditions, owing to the fact that detailed information and hydraulic analysis has not been performed for Dry Creek within the city. Through the analysis that this office has conducted, it has been determined that a division of flow occurs in the Dry A Creek flood plain in that area,west of College Avenue and east of the U.P.R.R. This"analysis showed that of the 2900 cfs design flow in this.area, a portion flows west across the tracks, a portion flows straight south and a portion flows east across College Avenue into the Evergreen Park area. The portion coming into this area coupled with local inflow makes aproper design discharge for this area to be 1850 cfs. Adjacent to the 4th'Filing of Evergreen Park lies the Lake Canal. Haying no viable means to pass Dry Creek flood waters, the Lake Canal poses a significant obstruction to flood flows. Using field elevations obtained by this office it is felt that the effective length -of Lake Canal which flood =, waters will pass across is 1700 feet. The Canal bank naturally varies in elevation so an average bank top elevation " was used for the reach. It was determined that a bank top of 58.16 was average. Two rating curves were computed using ,a different flow formulae, normal depth and weir flow. The normal depth rating showed that the water surface elevation for 1850 cfs would be 58.86. The weir flow rating showed that it would be 58.75. It should be noted that if the entire flow of 3200 cfs were used in this rating the normal depth elevation would be 59.05. _3 27 M Using the worst -case of these two ratings, the water surface elevation of 58.86 was chosen. This means that the water would be flowing 0.70 feet deep. It is noted that the Lake Canal bank near the south side of 4th Filing'reaches one of its highest points in this reach. Its elevation here is 58.80. To further use the worst -case, it is felt that the.depth of flow should be added to this nearby elevation.. The minimum protection elevation for this are should be 58.80 + 0.70 or 59.50 feet. 2s APPEtZIX irainage Area No. 1 Area = 113 acres Verticle Drop = 15 feet Length = 3,200 feet Coefficient of Runoff (C) A. Historic C = 0.2 for Agricultural land B. Fully developed -,Weighted value Type of Area - Acreage Light Industry. 50 Multi -Family Residential 40 Undeveloped 23 TOTAL 113 Runoff Coefficient 0.60 0.45 0.20 (50 x 0.6) + (40 x 0.45) + (23 x 0.20) Runoff Coefficient' (C) = 113 C = 0.47 Time of Concentration (TO - for Historic Condition From Kirpich's No for Small Drainage Basins, TC = 30. mirtutes x 2 (overland flow over grassed surfaces) TC = 60 minute's Rainfall Intensity (1) From City of Fort Collins Rainfall' Intensity - Frequency Curves, for a two-year storm at TC = 60 minutes i2-Yr = 0.90 inches/hour Design Peak Discharge for the Historic 2-Year Storm Runoff (Q) Q2-Yr. = CiACf = 0.2 x 0.90 x 113 ac. x 1.0 = 20 c.f.s. 29 Drainage Area No. 1 Detention Storage Requirements A graph of the Cumulative Runoff 'Method for determining detention storage for Drainage Area ill follows this design discussion. The required storage is 13.0 acre-feet. Outlet Control Structure for Lake 1 A Broad Crested Weir at the outlet will readily control the release rate.. The following approximate dimensions are required to actively store 13:0 acre-feet in Lake 1 while releasing 20 c.f.'s. *.The lake has an average surface area of.4.6 acres for the active detention depth (measured at 4966.0 contour line). Therefore, the depth of active detention must be 13.0'ac-ft a 4.6 ac = •2.85 feet above the outlet invert'. The highest lake water surface elevation should,be 4964.5 +.2.85 = 4967.35.feet above mean sea level, •.since the outlet invert of 4964.5 is most compatible with the downstream channel requirements. For H = 2.85' and Q .(release rate) = 20 c.f.s., and discharge in the Broad -Crested Weir determined by Q = CLH3�2 . Note: "C" values from King's Handbook of Hydraulics, P. 164. ., _3/2 C Q (ft) (ft) (ft) (constant) (C.f.s.) 2.85' 4.81 1.6' 3.28 25.2 2.85' 4.81 1.5' 3.31 23.9 2'085' 4.81 1.25' 3.32 20.0OK Use a weir length of 1.25 feet 30 Drainage Area No. 1 /-op oG we;?- 491oT,5' `-� `0-5 c=: ✓� �i�G�a.O .l --_ �� 0.15F2EE6�ADp ' Z.55, WE'C.O y D6PTK OF 49(6 7. 35 ACTivC DEi--+ 'E�fTio� l Drainage Facilities to. Handle 20 c.f.s. Release Rate A 25-foot wide drainage easement was given by the owner of vergreen Park to the ,City,of Fort Collins to allow construction an open ditch, or channel,, from the lake's outlet southerly along .he east boundary of Block 5, Filing 1 and then easterly along the north boundary of Conifer Street to Redwood Street. .Eventually the storm runoff released from,Lake 1 was to flow into Lake 2 at the southeast corner of Conifer and Redwood Streets. A "Vee"-type channel was called out in Filing 1 to handle the release discharge from .Lake 1. The same typical section was designed to "fit" the verticle controls of the outlet structure, the natural ground in the ditch alignment and the e4isting storm sewer at the intersection of Conifer and Redwood Streets. The channel profile. and typical section is included on the following page. u 5400 w 4500 LL 0 3600 0 Ly NEEMN N •.• w oZLE✓__L r i m, ' Lll 4: G 10 20 30 GO 90 120 TIME (min) 150 ISO CUMULATIVE RUNOFF FOR DETENTION REQUIREMENTS PROJECT EVc�G2�=tJ Pp2G i✓l4ST�7� L7eGlt.1/�C�C P_dVS BASIN. Dt=GItJnF�E G�Eb 1 DRAINAGE AREA 113 1a� TIME OF CONCENTRATION pL1=15 L_= 'ZOO' IC12PGJl b1�rcS TG = ZX 30=(oQ rniU. ASSI. Dza�ti70G6 RELEASE DISCH�RGE"Joesoorc P. )44' Coo �loa X �40G v. 113 = ZO GAS DETENTION VOLUME -=jp 4 - . V O L. , = SOOO 0 ly J v ID q(�-70 &5 1 495'S sEe►-� eoDuo 5 u41�-:� EI.JC b L4112 TO G 61- 12 % 34a'p 400' o, o, 0 INV. OG V' DiTGN GNC. OE i S 0 N ,ir 2' DEEP ' W �TTEO PE2�H6-TG�� a5•'�' H•fo4.suL1c. eeplu S = 0.9$ �?`/p) � V = Z. S�•Fp5 (1:484/n 22/s S'/z� l�=0.0030 V-4.o4 fps Qc 101.I GAS 24, -FPS Gj= /6Co.S Gf3 rl O.oZ-C, QAS'� 1Z. 5' TYPIcdL �EGTIOti1 <ji�E �iLOPE V4¢IES FQ01-� � 1 Qa Z' DEEP To 4 : 1 @ 3.1' OEEG I ut6l� Ex�hT� �ex�sT) 24" CF'(Exi2T 567 ouT LP�nUS HP A'T 3.1' CQEL6P GLowlNCo GLJ LL A2EC. = 39.1 S.G. WETTEo PE=1L1N 6TEe= Z5.0, 4 = 133 cX-, V d) 0. 00-jo 6.8-Fp`° �, s Z10 c.FS Y = g.afps Q= 32(o G'F''r 33 Drainage Areas 1 and 2 Combined Area = 211 acres Vertical Drop = 20 ft. Length = 4,800 ft. Coefficient of Runoff (C) A. Historic; C = 0.2 1 B. Fully developed; C = weighted value Runoff Type of Area Acreage Coefficient Light Industry SO 0.60 Multi-Famiiy 75 0.45 Single -Family 30 0.40 Undeveloped (owned by others) 56 0..20 ='(SO x 0.60) + (75 x 0.45) + (30 x 0.40) + (56 x 0.20) Cweighted 211 C = 0.41 Time of Concentration; for• Historic Condition From Kirpich'•s Nomograph, TC = 45 minutes it 2 TC = 90 minutes - Rainfall Intensity; for Historic Condition At TC = 90 minutes and 2-year storm, i2-Yr _,.0.68 in/hr. Design Peak Discharge for the Historic 2-year Storm Runoff Q2-Yr = CiACf = 0.2 x 0.68 x 211 x 1.0 Q2-Yr = 29 c.f.s. Drainage Areas 1 and 2 Combined Detention Storage Requirements A graph of the Cumulative Runoff Method for determining storage requirements for Drainage Areas 1 and 2 Combined follows on the next page. The total required storage is 22.3 acre-feet, with 13.0 acre-feet of that total provided in Lake 1. Outlet Control Structure for Lake 2 A Broad -Crested Weir at the outlet must actively store 9.3 acre-feet in Lake 2 while releasing 29 c.f.s. The lake has an average surface. area of 3.0 acres for the active detention depth (measured at 4958.0 ft. contour). There- fore, the depth of active detention must -be 9.3 ac-ft. 3.0 ac. =•3.1;feet above the outlet invert. The elevations of lots in the. Fourth Filing dictate that the invert eleva- tion of the weir., -type outlet structure be no lower than 4957.0 feet above mean sea level. Therefore, the maximum lake water surface elevation should be 4957.0 + 3.1 = 4960.1 feet. The.weir length was determined by Q = CLH3/2. For H = 3.1 f�_,•and Q (release rate) = 29 c.f.s.: H H3/- L C Q (ft) (ft)' (ft) (constant) (c.f.s.) 3.1 5.46 1.6 3.32 29.0 OK Use a weir length of 1.6 feet JS Drainage Areas 1 and 2 Combined 49le0.5 iJY OT. E6.2TL1EI•.1 �' WSTE2 sjUL'CA. G, ' ' P'L: �F 6GTIv. µ S. � I LC�)Gd) 1 CE►r-EUTieµ II -I I-nKE 2 I� WE12 I..-EI..3LsTN Drainage Facilities 'to 'Handle 29 c.f.s. Release Rate. A 25-foot wide drailiage easement was given by the owner of Evergreen Park to the Ci:ty,of Fort Collins on the east side of Redwood Street southerly of Conifer Street. The lot layout for Filing 4 dictates that the 25 foot wide easement be centered on the back line of the row of lo-�s'fronting on Redwood Street. This will require half of the easement (12.5,feet) to fall on the rear or side yards of those lots immediately east of the lots .fronting on Redwood Street. 'Yhe drainaae`,channel is for passing the over- flow from Lake 2 southerly to Lake 5 at the south limit of Filing 4. The channel profile and typical section..are included on the following page, 36 C� iJ IOIJ )=0� DZL�11JA�� 'L�Z�5&eD i 2 8100 5400 W 4500 Q LL W 3600 O Z KKKOM 1800 -Z ZNl T- / Gam✓ 1 V ry ' N � F w SI d,LL �6'�� y,4iE 10 20 30 60 90 120 150 180 TIME (min) CUMULATIVE RUNOFF FOR DETENTION REQUIREMENTS PROJECT `�2 c��EE-1 Pa�c t�1QST?2 ��AItJC.ro� PLL� 1�! BASIN s�zAlr-10 v� a,z�a 5 1 2 DRAINAGE AREA 21 c TIME OF CONCENTRATION OVF^ pw L vw' LS A= 2 o L_ = 4 Sop Fr. 'C.z�c.-: G�ss Tc = Z y.45 = ojo •r.,�. �.=hT ✓���vAS�ri c. w.LC oec RELEASE DISCHARGE P•i44• -73d/go DETENTION VOLUME -4 Co00 y- ZI�3,Se0 — �z-j f-•G—�T. LAIe BOT (02.0 62.0 61.G 60.7 &0•5 59.6 59.5 59.7 59.'7 59.% 59.E 59.1 59.o E6ST Ta7p eaA�1K Ka.S wESr roP gU LA! 9JW-3 O-[.v 601.6 1o1.W /ou.40 fOO.b wo.0 7 .'� 59.3 9U.0 tlm1 58'.b 5T2E T hTl EHT LE E _ roo.as o.9s saq.�, 49(00 `�" EAST TOP e,AUK � Li 57.0 4955 . • - _ _ _ Lal<_ _ 5 ems'4, LS5 K�(zU t= I L VEe-T. I" = 5, dT 3.1' VP.�4:1 21�E �iL•oPE A e EA = '5 0). 1 `NETTED �. Ic T»ZIVIBYETL = 25,8 u�oec_uL.IC. I�aPw� = I.52�s/o� V= 1.-7-7 aj = 40 9 e- Lt.T. �..'. ' V' t�IT�H 6ETWE�IJ h1OE gtrOPE �JLaE.IE � �e.�►-� C��TGI�]TIo1...11 Pol..1[�S 2 � 5 38 -ainage Area No. 3 Area = 100 acres Verticle Drop .= 20 feet Length = 3,000 feet Coefficient of Runoff A. Historic Condition; C = 0.2 for Agricultural Land. B. Fully Developed; Weighted Value Runoff Type of Area Acreage Coefficient Single -Family Residential 40 0:42 Undeveloped 60 0.20 'TOTAL 100 40 x 0.42 + 60 x 0.20 Runoff'Coefficient`(C) = 100 C = 0.29 Time of Concentration (TC); for Historic Condition From Kirpich's Nomograph; TC = 25 minutes'.x•2 TC = 50 (minutes _ Rainfall Intensity (i); for Historic Condition At TC = 50`minutes .and 2-year storm, i2-Yr = 1.03 inches/hour . Design Peak Discharge; for the Historic 2-year Storm Runoff Q2-Yr = CiACf = 0.2 x 1.03 x 100 x 1.0 Q2-Yr =' 20 c.f.s. . i n l Drainage Area No. 3 Detention Storage Requirements A graph of the Cumulative Runoff Method for determining storage requirements for Drainage Area No. 3 follows this design discussion. The total storage required is 6.0 acre- feet in order for Lake 3 to store the 100-year fully developed storm runoff from Drainage Area No. 3. Outlet Control Structure for Lake 3 This Lake, or•Detention Pond,.and its contributary drainage basin do•not directly'af€ect Filing 4 or future filings of Evergreen Park.. Howeve.r, a review of its design, and an alternative.design, are included for uniformity in the Master Drainage Plan. The lake has an average surface area of 2.8 acre-feet,for the active detention depth (measured at 4954:0 'foot contour),., Therefore, the depth of active detention must be 6.0 acre-feet .' 2.8 acres = 2.1 feet above the outlet 'invert. The highest water surface elevation should be approximately 4955.0 feet above mean sea level to avoid backing water into Conifer Street at the cross -pan entrance into Lake 3. The outlet invert elevation should be 4955.0 - 2.1 = 4952.9 feet. The Broad -Crested Weir length was determined by Q = CLH3/2 d" For H = 2.1 feet and Q (release rate) = 20 c.f.s.; H _ H3/21 L C (ft) (ft)- (ft) (Constant) (c.Qf.s.) 2.1 3.04 2.0 2.8.9 17.6 2.1 3.04 2.5 2.79 21.2 2.1 3.04 2.4 2.81 20.5 OK Use a weir length of 2.4 feet. Drainage Area No. 3 _55e iH Z )AEA-.12 A, DElv-r" O= - 53'� � a•GT t./E GE'r��:Ttc6.� �2.1 G�gT� • � = LEu[n-rN oc wStZ�Z.4 ��T� Drainage Facilities.to Handl-e:.20 c.f.s. Release Rate A 65 foot wide drainage and utility exists at the downstream end o.f the outlet control structure. Grading from the structure into the easement should be provided,. and the 65 foot:wi(%e easement should be graded to pass the released overflow to Lemay Avenue approximately 300 feet east of the outlef.-. 0 i ' :.. i4 6 ..J u 5400 w u 4500 3500 O z IIIIIIIIINK00M :u* I c Kam. �P 10 20 30 ''GO 90 120 150 180 TIME (min) CUMULATIVE RUNOFF FOR DETENTION REQUIREMENTS PROJECT BASIN DGGt��L+c aLBG ' 3 DRAINAGE AREA 100 Ac TIME OF CONCENTRATION �VcZ �yG 20 L= -5, Z, Lp,.�iH .Y- = G G,JE�j I T' G S = SC IT., N. ' RELEASE DISCHARGE Y /,o X Ic 0 - O cis 3 n s_ Gzv e c a>Nn�c c c P. 144 DETENTION VOLUME ,4-r Go a 35vo Drainage Area No. 4 Area = 30.2 acres Verticle Drop = 3 feet Length = 1,300 feet Coefficient of Runoff A. Historic Condition; C = 0.2 for Agricultural Land. B. Fully Developed; C =.0.42 for Single -Family Residential. Time of Concentration (TC); for.Historic Condition From Kirpich's Nomograph;"• TC = 20 minutes x 2 (overland''flow over grassed land) TC = 40 minutes Rainfall Intensity (i); for. Historic Condition At TC = 40 minutes and 27,year storm, i2 Yr = 1.21 in Design Peak Discharge for the Historic 2-year Storm Runoff Q2-Yr = CiACf =.0.2 x 1.21 x 20.2 x 1.0 Q2-Yr = 4.9 c.f.s. Detention Storage Requirements The Cumulative Runoff Method graph for Drainage Area No. 4 follows this design discussion. The total storage required is 1.9 acre-feet in older for Lake-4 to store the 100-year fully developed storm runoff. Outlet Control Structure for Lake 4 This detention pond is desi.gned to accept storm runoff from the northeasterly 1/3 of Filing 4 of Evergreen Park and much of the.area southerly of Filing 3. The lake has an average surface area of 1.25 acres for the active detention depth (measured at 4955.0 foot contour). Therefore, the depth of active detention must be 1.9 acre-feet : 1.25 acres•= 1.5 feet above the outlet invert. The top elevation of the Drainage Area No. 4 ponded water should not exceed the detention pond limits, which are at an elevation at 4956.0 feet above mean sea level in order to closely match the natural ground. The outlet structure invert elevation should be 4956.0 - 1.5 = 5954.5 feet. 1/2 The Broad -Crested Weir length was determined by Q = CLH For H = 1.5 feet and Q (release rate) = 5 c.f.s.; V 2 L_ C Q H H (ft) (ft) (ft),, (Constant) (c.f.s.) 1,5 1.34 1.0' 3.24 Use a weir length of 1.0 foot. 6.0 OR Drainage Facilities'to Handle 5 c.f.s. Release Rate A drainage "V" type,ditch or swale will be required to be graded from the overflow structure from Lake 4 north- easterly to daylight into the 65'foot wide drainage and utilities easement.southerly'of Lake 3. Additionally,'a 18 inch cor;egated metal pipe (Cb1P) will be required to .join the two portions of Lake 4. The culvert will allow the two areas within,Tract A of the 4th Filing to fill simultaneously and 'provide the necessary storage depth. scoo 8100 7200 6300 yo2 ✓� G ` Ipo uT,C I u 5400 �� �— w u 4500 r, v; O 3600 O' z D �I 2700 1800 10 20 30 90 120 150 18 TIME (min) M CUMULATIVE RUNOFF FOR DETENTION REQUIREMENTS PROJECT Ems/ ✓ G>� GEFJ Pd.G-lG _ !�i dSTc� -CJ2D 11JdC�� PL-AIJ BASIN. tDF- Ihl�C�i✓ b] 0 Q DRAINAGE AREA ZO.Z Ac TIME OF CONCENTRATION pC i4.P��u GIBES Tc= ' sae_ ZCs=91 _ o x ' RELEASE DISCHARGE 3 A�60 ,C 2 O. Z = /•� . �i c•F's 4i•s- 7ealUa� Nr>Nbscc:c �• 1� . DETENTION VOLUME !a-r ho m.�n. Ica-= = A 1 00 • 7-0. �A-3sf� 45 Drainage Area No. 6 Area = 34 acres Vertical Drop = 8 feet Length = 1,500 feet Coefficient of Runoff A. Historic Condition; C = 0.20 i B. Fully Developed as Light Industry; C = 0.60 Time of Concentration (TC) A. Historic Condition From Kirpich's Nomograph; TC = 16 minutes x 2 (overland flow over grass) TC = 30 minutes (I) B. Developed Condition; assuming the flow path remains 1,500 feet TC = 16 minutes.x 0.4 (overland flow over pavement) TC = 10 minutes (minimum) Rainfall Intensity (i) A. Historic Condition = 30 minutes and 2-year.storm, At TC T..4.8 inches/hour i2-Yr =. B. Developed Condition At TC = 19 minutes and 100-year storm, 1100-Yr = 7.2 inches/hour Design Peak Discharge (Q) A. Historic 2-year Storm Runoff Q2-Yr = CiACf = 0.2 x 1.48 x 34 x 1.0 Q2-Yr = 410 c.f.s. B. Developed 100-year Storm Runoff Q100-Yr = CiACf = 0.60 x 7.2 x 34 x 1.25 = 184 c.f.s. Drainage Area No. 6 Detention Storage Requirements An existing storm sewer system collects storm -runoff from Drainage Area No. 6 and releases the runoff on the south side of Conifer Street at the northwest corner of the Planned Industrial property (or at the northwest corner . of Drainage Area No. 5). There are seven catch basin inlets. in the storm sewer system. At an estimated 7 c.f.s. per inlet, approximately all that could be released south of Conifer Street wil•1 be 50 a.f.s. That is also the approxi- mate.capacity of the 30 inch -and ;7 inch circular reinforced concrete pipes (RCP's) combined•when flowing full. Therefore, the Cumulative. Runoff Method chart for Drainage Area No... 6'determines that 2.3 acre-feet of active storm runoff storage.ieill need to be provided in Drainage Area No. 6 to allow only 50 c.f.s., of discharge to be released under Conifer Street and into Drainage Area No. 5. If the storage is not provided on parking lots, rooftops, or elsewhere, the storm runoff in excess of 50 c.f.s. will flow easterly in Conifer -Street to Redwood Street. 1 Bloo 7200 6300 , v 5400 l G� w 4500 a a 0 360o Q� 2700 Iwo 900 10 20 30 roo. 90 120 150 ISO TIME (min) CUMUILATIVE RUNOFF FOR " DETENTION REQUIREMENTS :e'e cl-I PGV-K 11d5T�� fl�6 1 �d C�c PLd1J PROJECT BASIN, OZG Ida C�c �1==�Co DRAINAGE AREA TIME OF CONCENTRATION N /� 'ARGE '% GA-r�� DISCH ��^=' �s SO G �5 RELEASE DETENTION VOLUME 6.7- ZC VIOL. =• 's 000 X :�'�143 Drainage Area No's. 5 and 6 Combined Area = 87 acres Vertical Drop = 17 feet Length = 4,000 feet Coefficient of Runoff A. Historic Condition; C = 0.2 B. Fully Developed; Weighted Value Runoff Type of Area Acreage Coefficient Single -Family Residential 22' 0 :4 0 Heavy Industrial 30 0.70 Light Industrial 35 0.60 TOTAL 87 (22 x 0.4) + (30 x 0.7) + (35 x 0.6) Runoff Coefficient (C) = 87 C = 0.53 Time of Concentration (TC); for Historic Condition From Kirpich's Nomograph; TC = 37 minutes x 2 TC = 75 minutes (I) Rainfall Intensity (i); foi Historic Condition At TC = 75.minutes and 2-year storm, i2-Yr = 0.79 inches/hour Design Peak Discharge; for Historic Condition Q2-Yr = CiACf = 0.2 x 0.79 x 87 x 1.0 Q2-Yr -7. 14 c.f.s. Ii Drainage Area No's. 5 and 6 Combined Detention Storage Requirements A graph of the Cumulative Runoff Method for determining storage requirements for storm runoff from Drainage Areas 5 and 6 Combined follows this design discussion. The total storage required is 12.6 acre-feet. Storage must be provided in Drainage Area No. 6 to accommodate 2.3 acre feet of storm runoff in order to release 50 c.f.s. from the storm sewer system into Drainage Area No. 5.• Therefore, 10.3 acre-feet of storage must be provided.•in Drainage Area No. 1. 5 within. Lakes 5 and 6. The design of the"releas,e facility (30" sag culvert) and detention areas follows next after this discussion. ✓�T>=�TI�rJ NT9 r T• .. V u 5400 4500 LL O 3600 z 1800 GG' GOZ V. v� 9' N • Fi Di • 1— e ya�� 10 20 30 60 90 120 150 180 TIME (min) CUMULATIVE RUNOFF FOR DETENTION REQUIREMENTS PROJECT BASIN 17�d11`1LS <oE %52E�.Sr DRAINAGE AREA 87 c TIME OF CONCENTRATION �V�2L 4i�1D r�trUC� LLI-i = I-7 L= 4000l ejeajcA 37 RELEASE DISCHARGE (sg8 i �34 I k /o x 8- = 14 �s DETENTION VOLUME 4T IZO �' J �7GC TC- Cn30O 4970 ( 1 I i L M NjUI Q jF- 4S&5 tL n�cPw 00.90 B/6-t911.�'V' p1YGH ... 6 IC WA-rER. ' hTUEa 1 ' 06 24" QG � � q qe l•14 ,-IE` - . 4955 I --- I I — -- — •- -- uEvl 5lo te5�'� 0 1 0 ,050 N _. .. l IT _ •.._ TO....__ poor✓ I L.E hcn�.rc sloe. 1' = 200' I 61JD GULv6 ' _ � _= 46 L4K� B —4� 53.f39 .........� SAC:+ GUI-VE2.Y� QE3 L.F. N f \lam �al..T LAK �: C?t;T TUr1 4a.o / To f�edVlCE CEG�EAT. oI-1A4f Ste' r hn O,03 11� __411 Tor ..;Aw = 1.3Z x 3 = 4' Q-_-Ito V =5_1 fps P=i3.94 !1= SocFs