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HomeMy WebLinkAboutFile Documents.743 Cemetery Ln.0011.2018 (13).ARBK MOUNTAIN CROSS ENGINEERING, INC. Civil and Environmental Consulting and Design May 02, 2018 Ms. Gretchen Greenwood Gretchen Greenwood&Associates, Inc. 210 South Galena Street, Suite 30 Aspen, CO 81611 RE: Urban Runoff Management Plan—743 & 745 Cemetery Lane - Revised Dear Ms. Greenwood: The purpose of this correspondence is to evaluate the construction of a new duplex residence at 743 and 745 Cemetery Lane, from a storm water perspective and provide design recommendations pertaining to urban runoff management for incorporation into the site design. This letter incorporates review comments from the City of Aspen and replaces the previous letter dated December 20, 2017. These recommendations were generated from the site plans that were submitted to our office and a site visit performed on November 29 and December 13, 2017. Attached are plan sheets that show the design recommendations and details. Also attached are the drainage calculations that were generated. The project is at elevation of approximately 7880 feet above sea level and is adjacent to the golf course on Cemetery Lane. The project site currently contains an existing duplex building that will be razed prior to construction of the proposed new duplex. Ultimately runoff from the site will travel to Castle Creek and then to the Roaring Fork River after it travels through a series of roadside conveyances and storm drain appurtenances. Runoff from snowmelt is typically very large in volume but because it happens over a much longer time period, the peak flows are usually less than a rainfall event. Also, the Urban Runoff Management Plan states that they are not necessary at this time. Therefore storm water is defined in this study to be surface water that is a direct result from a rainfall event. No major irrigation structures cross the site. No other drainage studies specific to this site are known to exist. The project is located greater than 100' from any mapped floodplain or mud flow boundaries. Storm water from the site is evaluated in accordance with the standards of applicable sections of the City of Aspen, Urban Runoff Management Plan (Code). All flows are listed in units of cubic feet per second(cfs)unless otherwise noted. Methodology The design of a drainage plan begins with a calculation of the flowrate of water that will be produced from a rainfall event. Since the watershed basins are small (less than 90 acres), per the 826 1/2 Grand Avenue, Glenwood Springs,CO 81601 P:970.945.5544 F:970.945.5558 www.mountaincross-eng.com Cemetery Lane May,2018 Page 2 of 6 Code, the Rational method was used for estimating the amount of runoff that will occur. This method calculates runoff(Q) in cubic feet per second (cfs) from basin area (A) in acres, runoff coefficient(C), and rainfall intensity (I) in inches per hour: Q =C * I * A When acres and inches per hour are used as the units, the conversion into cubic feet per second is 1.008 but is usually ignored and it has been here. The runoff coefficient is a dimensionless coefficient. Basin Area Drainage basins have the characteristic that any precipitation falling within that area will drain to the same point of discharge. The project basins were delineated from project topography,project site plan, and building architecture. Runoff Coefficient A runoff coefficient is assigned to each basin that gives a relationship between the amount of precipitation that becomes surface water and the amount of water that is lost to infiltration, evaporation, or transpiration. The runoff coefficient is a function of drainage basin soil types, surface area, and/or land-use. Because the land-use and the surface cover often vary through the project, a composite coefficient is often assigned to each drainage basin, based on the weight of the areas and their respective coefficients. Rainfall Intensity Rainfall intensity is determined from intensity duration frequency curves, or IDF curves. IDF curves are graphs of, more or less parallel, frequency curves that yield rainfall intensities based on storm durations. Frequency: The return frequency of a rainfall storm is the statistical probability that a given storm event will occur on average in a given period.For instance a 100- year storm has the statistical probability of occurring once in a 100 year span or it has a 1% chance of occurring in any given year. It is important to emphasize that it is based on probability statistics and therefore does not reflect actual storm frequency. Storms of a 100-year magnitude can occur in sequential years, even in the same year. The return frequency of design is chosen and then referred to as the design storm. Duration: The duration of a storm is chosen to coincide with the time of concentration. Per the Code,the FAA Overland flow equation was used to estimate the time of concentration. The parameters needed to determine the flow elements include length, slope, and the Rational runoff coefficient. The theory states that if the duration is equal to the time of concentration,the length of time will be adequate for the entire basin to contribute flow. Mountain Cross Engineering, Inc. Civil and Environmental Consulting and Design 8261/2 Grand Avenue, Glenwood Springs,CO 81601 P:970.945.5544 F: 970.945.5558 www.mountaincross-eng.com Cemetery Lane May,2018 Page 3 of 6 Analysis Project basins were delineated based on a site visit to review existing conditions, aerial photography, roof lines, site grading, roads, project topography, and proposed and existing buildings. The site slopes from west to east with drainage trending towards Cemetery Lane. Cemetery Lane has a vegetated swale that separates the pedestrian path from the roadway that prevents run-on from the east. The neighboring property to the west is the golf course that contains a pond and ditch; additionally topographic survey shows a small berm along the west property line to prevent run-on trespass from the western property line. The southern property is an existing residence that has berming along the southern property line for the western portion and then is lower in elevation for the eastern portion. The northern property is another existing residence that is lower in elevation with a swale along the northern property line that drains toward Cemetery Lane. Presently, there is some runoff trespass onto the southern property and onto the northern property. The contributory areas are small but the proposed design will correct this. Other than the vegetated swale mentioned above, no adjacent storm conveyances exist. The historic and existing drainage basins were assumed to be the same. The proposed basin is slightly larger to capture the small areas that were trespassing to the north and south. Essentially, one drainage basin was delineated; everything in this basin drains to the bio-retention pond on the eastern property boundary. The proposed building will have hardscape and roof areas that will drain to turf areas before being conveyed by grass swales to the proposed bio-retention structure. Runoff coefficients were determined based on site soils and percentage imperviousness, per the appropriate figures in the Code. The hydrologic soil group was determined from Figure 3.1 and based on the project location is, "C". Based on the corresponding Figure 3.3 the applicable coefficients were determined and are shown in the attached calculations. The parameters for calculating the time of concentration were determined from the site, slope, length, and land uses. The time of concentrations for the site basins that were used are between 9.1 and 14.1 minutes. The calculations are attached. The rainfall intensities were determined by using the appropriate storm curve, duration to match the time of concentration, and the IDF curve provided in the Code for the City of Aspen. The basin flow rates were calculated for the 5-year and 100-year storms based on the Rational Method described in the Code for the historic (pre-project flows), existing, and the proposed conditions. The calculations are attached. Basin Area Coefficient Flow Description (acres) (cfs) Historic—5 yr 0.322 0.15 0.09 Existing - 5 yr 0.322 0.32 0.21 Proposed- 5 yr 0.326 0.40 0.29 Mountain Cross Engineering, Inc. Civil and Environmental Consulting and Design 8261/2 Grand Avenue, Glenwood Springs,CO 81601 P:970.945.5544 F: 970.945.5558 www.mountaincross-eng.com Cemetery Lane May,2018 Page 4 of 6 Basin Area Coefficient Flow Description (acres) (cfs) Historic - 100 yr 0.322 0.50 0.63 Existing - 100 yr 0.322 0.58 0.80 Proposed- 100 yr 0.326 0.60 0.92 Flows will be overland into swales. The swale sizes were determined using the Manning's equation for open channel flow. Minimum slopes of 1.5%,project flows,and vegetated lining was used for swale calculations. Minimum slopes of 1%,project flows, and corrugated metal was used for pipe calculations. Calculations are attached. The project is within the Castle Creek drainage basin and the proposed flows are increased from the historic condition so detention is required and proposed. Detention is provided by means of a bio-retention pond to mitigate increased flows from the project area. Swales convey flows into the bio-retention pond. Detention volumes were calculated using the modified FAA Procedure described in the Code. The required depth is 15.6"with 3:1 minimum side slopes. The pond has a north and south portion that is joined with a 12"pipe. Detention storage volumes for the 5-year and 100-year storms begin at an elevation of 7879.80, above the water quality capture volume that is discussed below. The 5-year volume calculated is 167 cubic feet and this is achieved at an elevation of 7880.25. The 100-year volume calculated is 275 cubic feet and this is achieved at an elevation of 7880.50. There is a slotted drain across the driveway at an elevation of 7880.67 that would serve as an emergency overflow in case of storms larger than the 100-year storm. Total pond volume is 436 cubic feet. The calculations are attached. Release rates from the detention pond match the historic flow rates for the 5-year and 100-year storms by means of orifices. The release for the 5-year storm is at elevation 7879.80 with an orifice of a diameter of 2.25 inches. The release for the 100-year storm is at elevation 7880.25 with an orifice of a diameter of 6.25 inches. The calculations are attached. Water Quality Temporary structures are intended to be used during construction activities. Permanent structures are intended to be used continually after the construction activities have been completed. Temporary erosion control measures that are to be employed during construction have been designed to contain sediment on the site and to mitigate erosion from construction activities. Silt fencing is placed around the downhill limits of disturbance. Rock socks are placed in the thalweg of swales and at inlets. Permanent erosion control measures are revegetation of disturbed areas, design of conveyances to prevent erosion, and the bio-retention pond. Additionally, the Code requires a Water Quality Capture Volume (WQCV)per the Figures 8.13 and 8.14. Mountain Cross Engineering, Inc. Civil and Environmental Consulting and Design 8261/2 Grand Avenue, Glenwood Springs,CO 81601 P:970.945.5544 F: 970.945.5558 www.mountaincross-eng.com Cemetery Lane May,2018 Page 5 of 6 The WQCV was calculated based on the site acreage and percent impervious area. Based on Fig 8.13 in the Urban Runoff Management Plan the watershed inches is determined based on the percentage of effective impervious area determined from the type of drainage system that is tributary to the impervious areas. Level 1 adjustment was used to determine the "Effective Impervious Area" from Fig 8.14. Based on the Effective Imperviousness of 48%,this yields 0.09 watershed-inches. Using the area 0.326 acres this yields 106.6 cubic feet of WQCV. The WQCV Structure is provided in the bottom of the bio-retention pond. The flat surface area of the bottom of the pond is 187 sq. ft. at an elevation of 7879.2. A depth of 0.6 feet is required to achieve the volume to an elevation of 7879.80. Type C soils require an underdrain rather than allowing infiltration. A 4" perforated PVC is proposed to drain through back to back reducers that would restrict flows prior to discharging to daylight. Drain time is estimated to be 1.5 hours. Calculations are attached. The site will disturb less than one acre and therefore will not require a permit from CDPHE. Maintenance Maintenance will be required periodically for the drainage system. At a minimum the following should be done bi-annually in the spring and fall: pipes, inlets, roof drains, downspouts, gutters, and swales should be cleaned and cleared of mud and debris. The bio-retention pond should also be cleared of mud and debris and also maintained with clean, straight grades. All heat tape should be checked. Heat tape should be turned off in the spring and turned on in the fall. Temporarily, the general notes require the maintenance and frequent inspection of the silt fence and the rock socks for proper operation. A management plan is included in the Appendix. Low Impact Development Principle 1: At the outset of the drainage design, WQCV was anticipated. The site grading was designed to convey runoff to the WQCV in the bio-retention pond. Principle 2: The design used the entire site attempting to minimize impervious areas. All flows are in permeable conveyances and discharge to landscaping. Principle 3: The impervious areas have been minimized as much as practical and still meet the requirements of the Owner. Principle 4: Similar to Principal 2, the impervious areas are minimized and flows are in natural conveyances. Principle 5: Detention is provided to mitigate peak flows. Principle 6: The WQCV facility is paired with the detention creating a dual purpose of peak mitigation and treating water to enhance the community in the bio-retention pond. Principle 7: The site has a treatment train approach in that drainage is conveyed in natural swales to the WQCV structure. Principle 8: All features are at grade and easily maintained. Principle 9: N/A. None of the facilities are located in areas accessible to the general public. Mountain Cross Engineering, Inc. Civil and Environmental Consulting and Design 8261/2 Grand Avenue, Glenwood Springs,CO 81601 P:970.945.5544 F: 970.945.5558 www.mountaincross-eng.com Cemetery Lane May,2018 Page 6 of 6 Results The magnitude of the peak runoff flows from the proposed condition is increased for the 100-year runoff when compared to the historic site. Bio-retention is provided that contains 436 cubic feet of detention and 106.6 cubic feet of WQCV. Natural swales convey flows to the bio-retention pond. There is a certain amount of uncertainty in hydrologic calculations. However, when constructed in accordance with this report and the drainage plan, it is our opinion that the design will safely convey the runoff flows and volume of the 5-year design storm event and the bio-retention required for this site and will not cause flooding damage to this or adjacent sites per the requirements of the City of Aspen. Thank you for the opportunity to provide this report. Feel free to call if you have any questions, concerns, or comments. Sincerel , • Mount n Cross E gin ring, Inc. V is Hale, PE 4` � /Z �$ Mountain Cross Engineering, Inc. Civil and Environmental Consulting and Design 826 1/2 Grand Avenue,Glenwood Springs, CO 81601 P:970.945.5544 F:970.945.5558 www.mountaincross-eng.com s • [ /!) t M. - j/ i • 4r,.. - - 1r ' 1 r. ,\ r , 110 i� 31111111. _ ii, ,A.._.... . r 3 Cemetery Ln -44. ,ilk isic • elk '11 Liki .. .. .. , .. 1 `,t s,.ip„,,, : s e ,„. _•._,,, ... ,„ .„.., $.. .• . ...,:, .....: . , . .. ,,,,,p_ . . s._.• , „.,_,..,t ..,, v .9d !V DATE 12/2o/17 FIGURE G U R E 1 5 1- .. 50' (".--------- MU(INTIiIN CROSS ENGINEER Chris Hale 743 & 745 Cemetery Lane 'i" ENGINEERING, INC. DWG FILE V Civil and Environmental Consulting and Design CemeteryLnDesign 826 1/2 Grand Avenue Glenwood Springs,CO 81601 JOB Gretchen Greenwood & Assc.'I ph 970.945.5544 fx 970.945.5558 www.mountaincross-eng.com 556-013 4 • c 7 E Historic ' hi Existing �. 2.2,i td N o i y C G \ z 1.4 U° 3 1.1 M w N N N irWd C (7 si o > ; W ts i N ° ° T7 c U :47 1 0 � , O W N Uaoa— — —DRAINAGE a — —�s78— BASIN a Ya ;4 11110.--- i — _las- ill ,-- -0----, _----._ *in ':- - s _ � 8, \ a 20 70 0 20 MMMMM tt SCALE: 1" = 20' a 1s i /_/ Ili \ \ �\ —7879 — y — — tll V- J. . ..—. • — — 4, „\ , :\ „ .. \ \ , .0‘ a ' , \I <\\ i tt / 0 ® I O 1 0.80 l/ \ I / 1 _ 1 11 ,1 0.58 0.32 \ / , w l ° z \ \ H ®� UJ 1 1 \ - - °' z yATIIFORTIMEOF 1 , CONCENTRATICn ON .10" X 1 as N. ,.• 4 ul W 37 e ,, 1 .� LEGEND I I 0 0 M i �1 ;-Iiiills11111 � / N 100—yr FLOWRATE (CFS) Cr I- 11 �.�.11,'� _ —\ ....,,.1 AREA (ACRES) ( _ RUNOFF COEFFICIENT gl A I c F.' o v rI N = O � N 'Ia otto t lio;... .F3g) § - — 6$1 3 P"' g 0 : . . . 0 insE4 v t) 0 c - o In ,- . 0 0 a) c ., \ . ...1 0 0 1 z Isimell 0 INFO = Ts CliWt *36tb LI° ID .4 l. 9 E1611 lart4 g g C DRAINAGE BASIN .L.... 5 co a, .,. t 7 d ' %. • _I . , .. .. .\ PATH CFEONRT TRIMTEI OF _ , ..','. .e 1........'..1 1tffL....L.k. ...L':. AON ..'1: . . • 2010 7 7 -.I. cr e) SCALE: 1 = 20 \ ..,,, \ 11 \ . ., • ., t.1 -- --- -- - 4 I* _ --,•• .--,-. --- \\ , • 4 %, \ • • •s 'K A-• --- OA ', \ \ \ . 1 . ., • FOUND ND.E.. . I - - - - - PO --.., 0 y ‘, .... .. I. trj i......110t,40.„, WA.. _ zw 21.a. ,..„,.'.,.. ., N•' . : \ , --- , ----- - ...., 1 1.3. . . 1 \.2. i • ' -------- • , '.. Sla • .f:::: fil VL VI--. - •Ar . a) . „ ._.._.:_._. s 1111116. o j Ca Z . ( _____.------ IA • C\ ,,,t >t < _„-- 1$ ---- . . . a) zili .1.0 E Liu:i _... ,... _ _,.......:„. i_,,,,.,.1_ _........H.,,,,,, :,,, \ii,"11, ''w.,,,,,,,,,::,., ,, 6) . i. a) 0 _....eiga,,,,_: _......... „ ,„, ,... . 0,,r) Lun ,.,. ____--- , t p -- _ _____-- . _ . a ( _ . _ I.._ la -,-- ..---1 . ..• '.......--- ' '...... ob 0 *11.IIIIIIIIIIIIb-\,,.- I7P2 ._,..,.- \ . ---- ...:A 1'''' '.< , LEGEND cc c . . . . ,.. . • . rk.i. . . . . . .. . . . . . . I , ... . • .. .. .. .. . , 100-yr FLOWRATE (CFS)—_ ' • AREA (ACRES) ------..-IQ---\\ --- 1 c co,PI 4 '--- . . . .. . . , . •. .• .. . .• . . .• . •.... :• - - RUNOFF COEFFICIENT .\ - -.1r- ..'l ...,..,-. a io at a 01 070 -.... c --_, ----.. _•.-." •• , • 4,4 , . -•• - -. - " ' - - - .• — 11:111111::'"111111117-,'" . , ... . . . - : .. : - -- •:•:.• --' • .... . -•-• • • ir) t .c — as la MO V —Roads `�:, HSG 1 L. Vto St• Rd C1 r % dilli —V 1` - A 111111"Nipr Spruce 6t IIIIN �-, .it �4,, Site 1��� Location a� L.. �— -s, I a / n� Flaunt 2.1 Natural Resource Conswnntlon Service(MRCS)Boll Map for Aspen 1 00 0 90 0 80 0 70 Area V —t-100-yr c 060 H i � —II—50-yes—a—25-yr E 0 50 x-10-yr U X tft r � —x—5-yf 0.40 fx re _��X'xx —e--2-yr max'' �� _ 0.30�X /x 0.20 I•' 0.10 000 L— — 0% 10% 20% 30% 40% 50-Va 00% 70% 80% 93% 100% Watershed Percentage Imperviousness Figure 3.3-Runoff Coefficients for NRCS Hydrologic Soil Groups C and D 1 00 o so 0 80 0 70 Area t 100- r P 060- y o u s—50-yr 0 050 —l-25-yt 0 lam' c X-10-yr o x x-5-yr 0.70 �x J* x�J� /x x 010 000 -- — 0% 10% 20 30% 40% 50% 60% 70% fl7,1 93' IO i. Watershed Percentage Imperviousness Figure 3.3-Runoff Coefficients for NRCS Hydrologic Soil Groups C and D DRAINAGE CALCULATIONS for MOUNTPiIN CROSS 7 3 8�745 Cemetery Lane ENGINEERING, INS 1 /20/2017 °' Civil and Environmental cnnsuldrrg and oe g 0267f2 Grand Avenue Gleawood Springs cob 6vl yt 070 9a555M fx 610.aC5,559axyrymonlnlnc .., '� Drainage Area : Historic PROPERTY GENERAL SURFACE DATA Total Drainage Area: 14,026 sq.ft. 0.322 ac. RUNOFF COEFFICIENT imperviousness= 0% HSG = C from Fig 3.3 C100 = 0.50 C10 = 0.25 C5 = 0.15 C2 = 0.04 100% 0.322 TOTAL BASIN ACERAGE 0.322 • � TIME OF CONCENTRATION Overland Flow Time Length Slope C5 Tc Upstream Elevation 7885.00 150 0.033 0.15 14.12 Dnstream Elevation 7880.00 Channel Flow Time none Length Slope K Tt Upstream Elevation 7880.00 0.0 10.000 20.000 0.00 Dnstream Elevation 7880.00 Total 14.12 min RUNOFF Historic Intensity Flowrate (in/hr) (cfs) 2-yr Storm 1.3 0.02 5-yr Storm 1.8 0.09 10-yr Storm 2.4 0.19 100-yr Storm 3.9 0.63 NOTES: - Soils are hydrologic soil group C from Figure 3.1 DRAINAGE C • AL LlLA idNS for I'A MO€INT IN CROSS 743&745 Cemetery Lane ENGINEERING, INC 12I20�2017 Civil and Environmental Consulting end Dc Ig e26 1)2 Grand Avenue Glenwood Springs,CO 81681 * --- Ph 8r0.015.616lI.nls.e/6.ststvnwirounlolnr,05®cng Drainage Area : Existing Surface description: Turf, duplex, and gravel driveway on an improved lot PROPERTY GENERAL SURFACE DATA Total Drainage Area: 14,026 sq. ft. 0.322 ac. RUNOFF COEFFICIENT sq.ft.or Land Use est. % acres imperviousness= 36% Building Roof 4010 0.092 HSG = C from Fig 3.3 Ponds 0 0.000 C100 = 0.58 Hardscape and Paving 1040 0.024 C10 = 0.4 Landscaped turf and planters 8,976 0.206 C5 = 0.32 Pine and Aspen 0% 0.000 C2 = 0.25 Sage and Grasses 0% 0.000 TOTAL BASIN ACERAGE 0.322 TIME OF CONCENTRATION Overland Flow Time Length Slope C5 Tc Upstream Elevation 7885.00 150 0.033 0.32 11.59 Dnstream Elevation 7880.00 Channel Flow Time none Length Slope K Tt Upstream Elevation 7880.00 0.0 10.000 20.000 0.00 Dnstream Elevation 7880.00 Total 11.59 min RUNOFF Proposed Intensity Flowrate (in/hr) (cfs) 2-yr Storm 1.4 0.113 5-yr Storm 2.0 0.206 10-yr Storm 2.6 0.335 100-yr Storm 4.3 0.803 NOTES: - Soils are hydrologic soil group C from Figure 3.1 DRAINAGE CALCULATIONS for MOIINTA1N CROSS 743&7 5CemeteryLare E,NGINEERINI ,e INC.1)4130�2D18 •., 02612 Grand Avenue clenwpotl Springs.co 81601 , --- pM19TAB19.55M fx 9T0.Bi5.9559 wnv.montafocroaac} Drainage Area : Proposed Surface description: Duplex, motor court, landscaping, and Improved lot PROPERTY GENERAL SURFACE DATA Total Drainage Area: 14,216 sq.ft. 0.326 ac. RUNOFF COEFFICIENT sq. ft. or Land Use est. % acres imperviousness= 48% Building Roof 5040 0.116 HSG= C from Fig 3.3 Permeable pavers 2890 0.066 C100= 0.60 Hardscape 1750 0.040 C10 = 0.46 Landscaped turf and planters 4,536 0.104 C5= 0.40 Pine and Aspen 0% 0.000 C2 = 0.33 Sage and Grasses 0% 0.000 TOTAL BASIN ACERAGE 0.326 TIME OF CONCENTRATION Overland Flow Time Length Slope C5 Tc Upstream Elevation 7884.00 37 0.016 0.40 6.55 Dnstream Elevation 7883.40 Channel Flow Time none Length Slope K Tt Upstream Elevation 7883.40 170.00 0.020 7.000 2.86 Dnstream Elevation 7880.00 Total 9.42 min RUNOFF Proposed Intensity Flowrate (in/hr) (cfs) 2-yr Storm 1.5 0.162 5-yr Storm 2.2 0.287 10-yr Storm 2.8 0.420 100-yr Storm 4.7 0.920 NOTES: - Soils are hydrologic soil group C from Figure 3.1 - Conveyance Coeficient for Lawn (7.0) per Table 3.3 Rainfall IDF for Aspen, Colorado 7 6 5 : i 4 _c t c i v Y ! c 3 2 5 10 15 20 25 30 35 40 45 50 55 60 Duration in Minutes -- .—2-yr —0—5-yr —4—10-yr i—25-yr —4-•50-yr - --100-yr WQC Volume, Area P ,� I4,' Level 1: Over turf to capture E ravd• ,tr` Tot Imp = 48 kt,, tv.•w c. • from Fig. 8.14 yields 4• r ``t. Eff Imp = 45 % r v r..ae.>r '� w it r�rt` N. from Fig. 8.13 yields s: f. WQCV= 0.09 watershed-in - f. — Area = 0.326 acres 6 Redd Volume = 106.6 cubic feet 'u J M)q ,. '0 %..j 0 ,: :O Rl 0: 00 01.I .. W Al .: IAA It gr ere i•nr v wss(p-i Lr11r! Figure 8.10 Imperviousness Adjustments far Laval 1 and 2PADCIA(UDFCD 1999) 0.30 - 025 1 ffi -5 0.20 c 0.15 ...0°Pilild:°11.1:11.°86.1del."..1....P.............°1°.....S7 , 0.10 8 0.05 0.00 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 Effective Imperviousness of Tributary Area to BMP(percent) ! Figure a.13 Aspen Wsbor Quality Capture Vokime - ,, DETENTION CALCULATIONS for ,, MOUNTAIN CROSS t ENGINEERING, INC 743 & 745 Cemetery Lane g',1and Environmmlal Consulting and Design 5261/i Gra�sd Avenue GlenwwdSprings.co SiSo1 w,e>ams .a,o�ss''s�w,..,'',..,,,,'.,o,�' .',n 04/30/2018 Area= 0.326 acres Tc= 9.42 minutes Release rate= 0.63 cfs C100 = 0.60 100-yr Detention Duration I Release Volume inflow Volume Volume Difference (min.) (in./hr.) (113) (ft3) (ft3) 5 5.80 272 344 72 10 4.70 366 557 191 15 3.90 460 693 233 20 3.50 554 829 275 25 3.10 648 918 270 30 2.70 742 960 217 35 2.50 837 1037 200 40 2.40 931 1137 206 45 2.20 1025 1173 148 50 2.10 1119 1244 125 55 1.90 1213 1238 25 60 1.70 1308 1208 -99 Maximum Volume Difference= Required Detention = 275 Cubic Feet Release rate = 0.09 cfs C5 = 0.400 5-yr Detention Duration I Release Volume Inflow Volume Volume Difference (min.) (in./hr.) (ft3) (ft3) (ft3) 5 3.00 38 118 81 10 2.20 51 174 123 15 1.80 64 213 150 20 1.50 77 237 160 25 1.30 90 257 167 30 1.10 103 261 158 35 1.00 116 276 161 __ 40 0.91 129 287 159 45 0.82 142 291 150 50 0.80 155 316 161 55 0.70 I68 304 136 60 0.60 _ I8I 284 103 Maximum Volume Difference = 167Cubic Feet North Portion Elevation Area Average Ends Depth (diff) Volume 80.50 507 80.25 433 470 0.3 117.5 80.00 368 400.5 0.25 100.1 79.80 314 341 0.20 68.2 79.20 187 250.5 0.60 150.3 436.1 Cubic Feet WQCV = 106.6 cu.ft. Flat area of 187 sq.ft. at elev. 79.20. Flat area volume is a depth of 0.6' 5-yr detention volume begins at elevation 79.8 = 168.3 Cubic Feet 100-yr detention volume begins at elevation 79.8 = 285.8 Cubic Feet Total pond volume = 436.13 Cubic Feet Orifice Calculations = 5 Q = 0.089 cfs < 0.09 cfs C = 0.600 A = 0.028 sq. ft. 2.25 diameter (in.) H = 0.450 ft Orifice Calculations = 100 Q = 0.111 cfs C = 0.600 A = 0.028 sq. ft. H = 0.700 ft 2.25 diameter(in.) Plus Q = 0.513 cfs C = 0.600 A= 0.213 sq. ft. H = 0.250 ft 6.25 diameter (in.) Total flows = 0.111+.513< .63 cfs Channel Report Hydraflow Express Extension for Autodesk®AutoCAD®Civil 3D®by Autodesk, Inc. Wednesday,May 2 2018 Swale Triangular Highlighted Side Slopes (z:1) = 4.00, 4.00 Depth (ft) = 0.36 Total Depth (ft) = 0.50 Q (cfs) = 0.920 Area (sqft) = 0.52 Invert Elev (ft) = 1.00 Velocity (ft/s) = 1.77 Slope (%) = 1.50 Wetted Perim (ft) = 2.97 N-Value = 0.030 Crit Depth, Yc (ft) = 0.32 Top Width (ft) = 2.88 Calculations EGL (ft) = 0.41 Compute by: Known Q Known Q (cfs) = 0.92 Elev (ft) Section Depth (ft) 2.00 1.00 1.75 0.75 1.50 0.50 v 1.25 0.25 1.00 0.00 0.75 -0.25 0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5 Reach (ft) Channel Report Hydraflow Express Extension for Autodesk®AutoCAD®Civil 3D®by Autodesk, Inc. Wednesday,May 2 2018 12 in. Pipe Circular Highlighted Diameter (ft) = 1.00 Depth (ft) = 0.47 Q (cfs) = 0.920 Area (sqft) = 0.36 Invert Elev (ft) = 1.00 Velocity (ft/s) = 2.52 Slope (%) = 1.00 Wetted Perim (ft) = 1.51 N-Value = 0.022 Crit Depth, Yc (ft) = 0.41 Top Width (ft) = 1.00 Calculations EGL (ft) = 0.57 Compute by: Known Q Known Q (cfs) = 0.92 Elev (ft) Section Depth (ft) 3.00 2.00 2.50 1.50 2.00 1.00 1.50 0 0.50 1.00 0.00 0.50 -0.50 0 1 2 3 Reach (ft) Channel Report Hydraflow Express Extension for Autodesk®AutoCAD®Civil 3D®by Autodesk, Inc. Monday,Apr 30 2018 8 inch PVC Pipe Circular Highlighted Diameter (ft) = 0.67 Depth (ft) = 0.44 Q (cfs) = 0.920 Area (sqft) = 0.25 Invert Elev (ft) = 1.00 Velocity (ft/s) = 3.75 Slope (%) = 1.00 Wetted Perim (ft) = 1.27 N-Value = 0.013 Crit Depth, Yc (ft) = 0.46 Top Width (ft) = 0.64 Calculations EGL (ft) = 0.66 Compute by: Known Q Known Q (cfs) = 0.92 Elev (ft) Section 2.00 1.75 1.50 (---- :--- 1.25 1.00 0.75 0 1 Reach (ft)