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HomeMy WebLinkAboutDrainage Reports - 05/31/2018%�etli5ion �b DP. inw.l City of Ft. Collins rovp Plans` repoi t dk a to K or Approved By 5 d»�en�. October 25, 2017 Date Jr -» g BASELIE�N�Em Revised: January 30, 2018 - Wes Lamar ue Engineering Planning - Surveying J q � Development Review Engineer t4l, City of Fort Collins 281 North College Avenue Fort Collins, CO 80524 RE: Drainage Letter - Kappa Kappa Gamma CSU House Expansion DRAINAGE The following letter explains the design and intent of the developed drainage plan for the Kappa Kappa Gamma CSU House Expansion. The scope of this project includes expanding the structure of the sorority house, adding additional parking, and an underground detention pond to direct flow into the City storm sewer system. With an increase in imperviousness of 6,427 square feet over the existing conditions, this drainage letter provides enough information to approve the drainage design in lieu of a drainage report. The site is located at 729 South Shields Street in the northeast quarter of Section 15, Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. The project area lies on the west side of South Shields Street between West Plum Street and West Laurel Street. The project area ground cover consists entirely of soil type C. The site lies outside of any floodplains as shown in the attached FEMA Firmette. The total area of the site is 1.1 acres with existing and proposed imperviousness of 53% and 66% respectively. According to the Old Town Master Drainage Report any increase of imperviousness over 5,000 square feet will require onsite detention to account for the increase. The proposed site increases the imperviousness by 6,427 square feet, which will be accounted for in the underground detention area as well as the water quality capture volume (WQCV) for the entire area draining to the pond. Basins P1 and P2 encompass almost all of the additional impervious area and is routed through the water quality detention system. The undisturbed areas will be left in their historic conditions and not accounted for in the detention pond. The disturbed area to the north of the proposed patio will drain off -site, but maintain the existing historic runoff flow rates. The allowable release rates were calculated based on the historic flows and outlined within an email to the City of Fort Collins found in the appendix. The City of Fort Collins' mass balance approach to detention was used to determine the additional required detention volume. The outlet structure is based on the ponding depths and orifice/weir equations to limit the maximum allowable release rate from the underground detention. Corporate Headquarters Northern Colorado Rocky Mountains 1950 Ford Street 4007 S Lincoln Avenue, Suite 405 419 Oak Street, PO Box 770152 Golden, Colorado 80401 Loveland, Colorado 80537 Steamboat Springs, Colorado 80477 Ph 303.940.9966 Ph 970.353.7600 Ph 970.879.1825 Fax 303.940.9959 Fax 066.242.9106 Fax 866.242.9106 Pagel 2 The WQCV and additional detention-for_the'site_will be,treated`in an underground detention system (ADS Stormtech or equivalent) at the southwest corner of the lot with an outlet that will discharge into the public storm sewer system. The WQCV will be treated through the implementation of isolator rows within the underground detention system. The mass balance of the actual inflow and outflow based on '/z the filter fabric capacity was checked to make sure enough volume is provided in the isolator rows. The total pond release rate will be controlled by an orifice within the outlet structure. The outlet structure has been designed to release the detained volume at a max outflow of 3.81 cfs. The allowable outflow is calculated based on the total historic release rate minus the offsite flows. The additional required volume was calculated using a mass balance method, which incorporates the City of Fort Collins' OF curve as inflow and the max allowable pond release rate as outflow. The outlet structure also utilizes an overflow weir for any volume above the required 100-yr volume. Any volume above the WQCV will overtop the isolator row inlet structure and flow into the rest of the underground detention chambers. The additional chambers have been provided to account for the increase in imperviousness. The outlet will tie into an existing storm structures at the corner of West Plum St and Aster St. The WQCV required for the site is 807 tuft which is .achieved through 27 SC-310 chambers. The additional required detention volume is 681 cult and is achieved through 22 SC-310 chambers. Additional volume in the perimeter stone area brings the total volume of the underground system to 1,901 cult. The runoff generated by the site reaches the detention pond via overland flow, curb and gutter, and storm sewers. The parking lots drain to combination inlets in a sump condition. The capacity of these inlets can pass the 100-yr storm with a maximum of 6 inches of ponding. The inlets flow into 15" PVC pipes at 0.5% slope. These pipes have the capacity to convey the 100-yr storm within the pipes. For complete calculations see the appendix materials. Below is a summary of the drainage basins, detention volumes, and outlet structure. Table 1: Drainage Basin Runoff Summary. TOTAL PERCENT 2-YR 100-YR DESIGN BASIN AREA Cz C+oo IMPERVIOUS RUNOFF RUNOFF (ACRES) (CFS) (CFS) HISTORIC BASINS Hl 0.43 0.87 1.00 90% 0.98 3.90 H2 O.36 0.35 0.44 21% 0.27 1.19 H3 0.28 0.48 0.60 37% 0.29 1.25 DEVELOPED BASINS Pagel 3 TOTAL PERCENT 2-YR 100-YR DESIGN BASIN AREA C2 Ct00 RUNOFF RUNOFF (ACRES) IMPERVIOUS (CFS) (CFS) P1 0.49 0.89 1.00 90% 1.26 4.90 P2 0.12 0.95 1.00 96% 0.33 1.18 0S1 0.04 0.35 0.43 i 21% 0.03 0.14 OS2 0.20 0.46 0.58 34% 0.23 1.01 OS3 0.21 0.47 0.58 35% 0.27 1.18 DETENTION BASINS WQCV (TOTAL SITE) 1.07 0.71 0.9 66% 100YR EXISTING IMPERVIOUS 0.56 0.95 1.0 100% 1.54 5.60 (EX TOTAL SITE) 2YR EXISTING PERVIOUS (EX TOTAL SITE) 0.51 0.20 0.3 2% 0.22 0.95 100YR UNDETAINED 0.46 0.45 0.6 33% 0.46 2.01 (OS1+OS2+OS3) DETENTION INFLOW 0.61 0.90 1.0 91% 1.58 6.08 (131+132) Table 2: Detention Summary DESIGN BASIN TOTAL AREA PERCENT VOL REQ VOL PROV (ACRES) IMPERVIOUS (CU-FT) (CU-FT) WQCV (TOTAL SITE) 1.07 66% 807 837 ADDITIONAL IMPERVIOUS OAS 100% 681 1064 DETENTION TOTAL - 1488 1901 Since runoff from proposed improvements is captured by an underground detention system and released into the public storm system at the allowable rate, and offsite drainage follows historic patterns and flow rates, this site complies with City requirements for stormwater criteria. Pagel 4 Sincerely, Baseline Engineering Corporation, Noah Nemmers, PE Pagel 5 REFERENCES: 1. Fort Collins Amendments to the Urban Drainage and Flood Control District Criteria Manual, City of Fort Collins, Fort Collins, CO. February 2013. 2. Larimer County Stormwater Design Standards, Larimer County Engineering Department, Fort Collins, CO. June 20, 2005. 3. Urban Storm Drainage Criteria Manual, Volumes 1-2; Urban Drainage and Flood Control District, Denver, CO. January 2016. 4. Urban Storm Drainage Criteria Manual, Volumes 3; Urban Drainage and Flood Control District, Denver, CO. November 2010. W ° -m myCE w < < mc� ®° W 061- ( ILLU $n W UJ W ao W c �i Ev o E O a O OO m O�YLL g g F e- %N U w f" C ° v o? W ♦- J ��` Wpm fi � a£o z m w> (D Q amg�d�e C o m O a o m �z o b w %. Q ppyy €Eg =!v°n ( no la W J Q 1 f� Z W p� a o �A/ a O D yc" - mom of r. v IE .tm. E E a c Jn'«w cl O m Q a J�� o z a as a`$ n O L 9`• V/ LLII I�4L VL ( OO�E ���III 'QJ E'i ! EE mg li L qqu a J SCLm6 �0 m3Ym 10 ° m E 3 of""8 VAI t5 a _ `p mmmmo €3o«a m a v 6L6013NVd SNio AV NUE N ; ¢ , `ili76 w w 3AIH0 A90W 3NAVM W a MONlE a °_31HON 130 w Z N J w W 3 133biS S(1131HS H w w w 7 3 Z NDJVM COY N U 0 Q 1S11393me Lu w U ) < > DnN3AV1100S ¢_ C,� 0 0 w 3AIUG m w 83lllW J w } Q CL Q a N w Q 0 w ZO Z 3 w ¢ C) m J U d. w 31N3AV NHVd AEO w 3 iF w = z U L j w Q N�. > m 1 Cot" W Co"�tit9 o w et y F VpKE�' ' n.1�"� a yys W V 3 e O ti N a otewor M SY5 so M.fi .S oSol fi OlBWVY pp p� M.sys aS01 f- a T N Z 7 N T 0 jN y m N N 6 3U m o g 6 m a a u CCCCC R x � UN � ry O C O � C =Q 2U m. .5 oSol Q� n d E U L N N m n w N N q U N ry Q QQ�� E m'o E 35 AD o m c4 y 'om E C u_ q W _ O N N n N W D E N N O O O w d D tO E VEl C N L q N a �• 6 N ° ii C ry d N U Q: O 6— O °' a L ..: a C a 'm mn3c E CO) W nmatd v! mN m ¢ 3 Euoin D t o v m Q d A o W a T > ° t`oom _c> c ° o y m�cj=, ci E0 o' N s E T�oN n ot D N y 2D� m J N is O y oa Uc n m.Ed 'W n w E L N OJ n n y D > J ° 4 m 0 02 n 2 E n.Q 6 a O O C y O N O n -En m E c F T d �j m L d N v rn9 A a m $ o�yw oc m2—' t .o 10_ He Q� !'.'M m DD aW 0 " E� U) �.� E 1 ° ppN °O O Q 60N N�oy Ly 53CW! me4M1aULm u o oN mp . N C O SU- 'i E !Zm aE w C) F o yO 0EwE=o a W j W C W m T W � U L Q ❑ R@ 'p W 'm C U U p ❑ 2 0 y � L v o a W W 0 _ C o Qo O m a m m y° ❑ ❑ ❑ g 7 W a m a ❑ z m a ❑ ❑ W p O 0 0 m o m a y W a W 0 e mg a ❑ ❑ n a° ❑ ❑ a m m 0 �❑ o,a a m m m z Hydrologic Soil Group—Larimer County Area, Colorado Hydrologic Soil Group Hydrologic Soil Group— Summary by Map Unit — Larimer County Area, Colorado (COS") Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 74 Nunn clay loam, 1 to 3 percent slopes C 1.1 100.0% Totals for Area of Interest 1.1 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long -duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink -swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff.- None Specified USDA Natural Resources Web Soil Survey 4/20/2017 Conservation Service National Cooperative Soil Survey Page 3 of 4 Hydrologic Soil Group—Larimer County Area, Colorado Tie -break Rule: Higher usDA Natural Resources Web Soil Survey 4/20/2017 2111111111111 Conservation Service National Cooperative Soil Survey Page 4 of 4 (11) Section 4.0 is amended to read as follows: 4.0 Intensity -Duration -Frequency Curves for Rational Method: The one -hour rainfall Intensity -Duration -Frequency tables for use the Rational Method of runoff analysis are provided in Table RA-7 and in Table RA-8. Table RA-7 -- City of Fort Collins Rainfall Intensity -Duration -Frequency Table for Use with the Rational Method (5 minutes to 30 minutes) Duration (min) 5 2-Year Intensity (in/hr) 2.85 10-Year Intensity (in/hr) 4.87 100-Year Intensity (in/hr) 9.95 6 2.67 4.56 9.31 7 2.52 4.31 8.8 8 2.4 4.1 8.38 9 2.3 3.93 8.03 10 2.21 3.78 7.72 11 2.13 3.63 7.42 12 2.05 3.5 7.16 13 1.98 3.39 6.92 14 1.92 3.29 6.71 15 1.87 3.19 6.52 16 1.81 3.08 6.3 17 1.75 2.99 6.1 18 1.7 2.9 5.92 19 1.65 2.82 5.75 20 1.61 2.74 5.6 21 1.56 2.67 5.46 22 1.53 2.61 5.32 23 1.49 2.55 5.2 24 1.46 2.49 5.09 25 1.43 2.44 4.98 26 1.4 2.39 4.87 27 1.37 2.34 4.78 28 1.34 2.29 4.69 29 1.32 2.25 4.6 30 1.3 2.21 4.52 33 Table RA-8 -- City of Fort Collins Rainfall Intensity -Duration -Frequency Table for Use with the Rational Method (31 minutes to 60 minutes) Duration ( min) 31 2-Year Intensity (in/hr) 1.27 10-Year Intensity (in/hr) 2.16 100-Year Intensity (in/hr) 4.42 32 1.24 2.12 4.33 33 1.22 2.08 4.24 34 1.19 2.04 4.16 35 1.17 2.0 4.08 36 1.15 1.96 4.01 37 1.16 1.93 3.93 38 1.11 1.89 3.87 39 1.09 1.86 3.8 40 1.07 1.83 3.74 41 1.05 1.8 3.68 42 1.04 1.77 3.62 43 1.02 1.74 3.56 44 1.01 1.72 3.51 45 0.99 1.69 3.46 46 0.98 1.67 3.41 47 0.96 1.64 3.36 48 0.95 1.62 3.31 49 0.94 1.6 3.27 50 0.92 1.58 3.23 51 0.91 1.56 3.18 52 0.9 1.54 3.14 53 0.89 1.52 3.1 54 0.88 1.5 3.07 55 0.87 1.48 3.03 56 0.86 1.47 2.99 57 0.85 1.45 2.96 58 0.84 1.43 2.92 59 0.83 1.42 2.89 60 0.82 1.4 2.86 34 ; |:l;,■ r !` !`- {k/§§! ! !I �k ! > $! ll... . , ! | !!!! § ) � | |«!« ) ! ` !2g �« |�:s■B„ ; � f|! §§B ! !. ! || $|B§§§§ § | � ! | § ! � �\;; ■ , , ■ ,!!.`- ( t>a #! 19 /|! • | ! �|! • | § | `!, . . � ■ t ! � |uIr|ru.| ! ~ \a f \O !.!! ! }!]! . _#! } ! |... { } f ! |J! }Ali ` \ \ ! |s• •-.,. | /Re }� | \ee � /ee \22 dRe | � |!|..... f | �.... ! � | |..... ! , �..... f \ee ! ! _ ! |g ©! � | ;R e; ll,,.,, � �•! . „ |. - | ! ! ! ! ! | • - ! , | | i | � ! _ | | , - §,,., \ ` � !§!!!,|!! • �/§£! 0 o m �n O Ol N ct M N d w m t V Q Y T m r Ol ry OI N N 01 n 0 0 0 d F c a c O 2 — C E > r1 C V O F C V O V > O � r ti rl � E c v u u v u zt- Q U d m M a m M m N O F- C O � c C - q m T O O O � N m V O O1 N Q .y d v m L Q > o M m r N V N m 0 N N y o 0 0 0 d L � m •o m m N c w c w � m m Vl m v1 c m m m a n q N N N N N N n — C_ E T C V O H q C V O V T D E F U O O 0 O o m a 0 in m m c w u m u C T m m m r � c Q U N _ A V � O O O O O O H C O E `o c c — C � D1 A n m N N N e4 N m Ip n n M N O 000 F C O m i 0 o ID01 n 0 m O O N 10 d v m L N O y T Q N 10 m n d c Z c N c C [O N m y K — C_ E 5 C O F C N c O U > O = v E r U T 0 o vi r O c v V S v u U — n Lll a m m O 0 O O O F C O o > o 0 3 N w 0 W W Z M c W a Z !- 2 F 2 O o O p> _O a F C ✓� K Z K W M .. O O N O Project Inlet ID: ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor 6 Major Storm( Slops, BelaM Curb heave blank far no mnveyana vee+DNUM aTl ,, s R.,hneac E.. Curb (pypca0y beMean 0.012 all 0020) Guner Flow Lne IL Faa I. Street Crown Tren—nec sloe Crass Slope MW<alp 2Incnes eser 24 mNea or 0 083 nH) L.Vp ofinal Slaps � En., 0 for aomp mnStion y's Roughness for shave Seca., IM1mcaty between 0012 all 00201 Avcwswd Spell Iw Marc, b Map, 6twm A]pwaMe Deal. at Guide, FlcMre 1w Ahror 6 sx or Slam k w.es arc na appk,bk.n Su roe. - STORM Allowable Capacity a based on Depth Criterion STORM Allowable Capachy Is based on Depth Cri eiwn Tys= sa.,. = .. Hcs= T:n 5,rib so n rva archer n mri B ago 0013 M03 .no, Sbrm Mala Sbrm Tu - 50 100 A 0, 40 60 Irchas r r .boor Stamp Ma S. Oyga SUMP SUMP Ns co3176-UO Inlet v4.05alsm, Type 13 Combo Inlet all8 011, 10.3E AM INLET IN A SUMP OR SAG LOCATION Venter. 4.05 Pat ansnd March 2017 LC (C) H-Curb H-Vert WC W WP L.(G) In Information (anoint of Inlet COOTeDeaver 13 Combination T Pa' Oeplaxelon (etltllllonxl to curb muous Buher tlepression'a'bom above) a,,o,-a• tar of Unit lads (Good or Curb Opening) No r Dardi at Flowlne(oubWe of loco[ Jepraddlod Pending Death- llnformatlon h of x unit Ga. L„ (G) ofa Unit Grate W, OpendO Rep. Id a Gnto Mid-1 vaWes 015D 90) A — ling Fehr fora Single Grate(tyMul value 050-0 70f C, (G) Won Cape ... t gNI veto. 315 -].60) C_ Of+ Caeca CCaenvnl (rypnal value 060 - 090) C, (G) Opening Intermeted b 01 a Unit Curb Created 4, fc) 11 C11raMot Curb Conrad, IP Inches H, it of Curb oxide Throat in Inches '41— of Throat (sae USOCM Figure 5T-5) Thele. Kolb for oepreselon Pon it pally the crimewan n o12 fee,) W„ png Factor for a single Curb Opening (typical value 0.10) C, (C) - Opena, Warr Coeficient(lypiceI vehm 2 3-3.]) C.,(C)- LOCTIOenver U CCmdnvmn i 00 ]I aches 9 an as MAJOR F O—nimi Caputo feet feet 3.00 t )3 043 O50 050 3]0 060 .'In Upace, churce Ca.... ded tlypical value o.bo-o./o) Grate MINOR MAJOR Cloggleg Component for Mideplo Unlla Coel= 1.00 1,00 Lloh", Factor lit Munlylu Unlla CIO, ' a. 0 50 Grate Capacin,as is Mir (based on Modified HEC22 Method) MINOR MAJOR dtemdame without Meeting 0. Intetcepeon in Cloggltt0 C_ • OS 16 cfs Grans Capadty as is Of lbawtl on tilde ed HEC32 Mot MINOR M1YJOR Iderapunn wooden Cm„mg O,• 57 I0 Cis Inhadir0.n MN Cl.pgmg 5 do Grad. Convert, as Mx lad Flow USE MAX CAPACITY MINOR MAJOR Interruption w0 SINCE IN SUMP' cfs C in CIue"an Interdiction vetM1 00m0 3.5 CFS 0,..= t 1 3.3 h ..__..,.,__.._..................___ ._ __. ___...__. W/SOM CLOGGING ,• mg CooMcard for MUII1p'. Units Co. Img Factor lot shares Urals Clog Opening as a Mir Ibased on Modified HEC23 Mistreat spoon edged Clogging 0. .gave Mm C"'an, G, Opening as on Ortlln (based on located MEC33 Method) spoon wNoul corcep q Oa .,be. d in clogged, 0. OPannng CoP¢xy as Mixed Flow USE MAX CAPACITY .,loon "Imma Clo,gmg SINCE IN SUMP' Q, action mm Cl..Prn. Ad CFS 0 ..__....-. ..___,__---- W..___.__ .___.__ .,.._ W/ 50% CLOGGING L.n9m Street Flow Spread (named an street geomeln' from dowel Flow WPN at Street Clever for Game f.9d.ddm do for CUN Opening Weir Equation ADD GRATE & do ndoonlnletPerformance Rctuforlos RF— )pemg Performance RedocmrFaerbe glided CUROPENING Rp Intel PerxOrmane Redunlon Fader fortaLalbs6 MAX CAPACITY RFC.,, 7.9 CFS All SM CLOGGING Inlet Interception Capacity(assumes clogged condition) 0.^ ING: Inlet C... me, Weir than 0 look far Minor and Marar Slomia O,.c.. e... ....,. MINOR MAJOR 0279 040 0.09 024 C.ae 0 ]6 t g0 1 he 048 09e a., I 2.0 Ids co3176-UD-Inlet_v9.05. spend Type 13 Combo Inlet 8r18M17. 10 38 AM d w a m 0 N O (`1 N `m O m N C O 0 n E z 0 0 O O Cl N N tNl 9 Q aa� i ul Yl NI th � (V Yl O m N N N N C x N N N N N N y. O O N O N O m O YI O N O m p r a In in o o r of � LL lC 0 tp IO G N U LL K TJ m V N � O O m m Ip m m a O O O O O G 1A m Ill tp N 1A O N m N m T O O O O O O m m m IA m N O O O m J3 y o 0 0 m mm Imp tmo N J m C y C J J O = IOp � lL L W B C O .A z LL 2 0 0 0 0 0 0 t7 Of t"I N f9 M O 0 r N @ N N H 0 0 rn m 0 r 0 a L � U N N O ;no 9L'9E09'13 'AEI 96'9309'13 Wily ► w1- B9EIM RB N J W ry S Ul LE'9LC9 13 'AUJ lnCl 9L'►L09'13 *AUK 88'9d09'13 Wlb 00'00+0 Its 0 G G G C o o O o O O O O > 0 QJ 1A 0 N 0 N 0 �(I 0 N 0 N w 0 0 0 0 00. 0 ;no 49'60a0' o £fY g:oi -eag• 0 0 0 m 0 � U N N of N a 0 n J W O N O C7 U1 8B'gt ;no g0'gt Wee 00' o 0 0 0 0 0 N 7 N 7 N N O N N N N > Q) I[I o 0 N 0 N il] 0 0 h Vl 0 W O O O O O O O O O O N O O O O t0 N m V @J O ry N 1no cw, MEMOMMUMAJ ;no N L :u, r O N N t N O O n G w UI irl0 e x ul ¢9' ill17� o - 0 o 0 0 0 0 0 0 0 0 0 0 O > O O N O m O O NO O O O N N N V] N 10 W w Q� O a w � � 5; ) }2 f § 3 § § 2 J| k § § ! S 5 ) ! (1) �g s C S (UW a 5 Md �88a�� -F3 9Hill Z \§) E! � )§!6 -§§®§ - E222|!e SO!!( No Text No Text No Text Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. 8in Corrugated HDP Capacity Circular Highlighted Diameter (ft) = 0.67 Depth (ft) Q (cfs) Area (sqft) Invert Elev (ft) = 100.00 Velocity (ft/s) Slope (%) = 1.00 Wetted Perim (ft) N-Value = 0.012 Crit Depth, Yc (ft) Top Width (ft) Calculations EGL (ft) Compute by: Q vs Depth No. Increments = 1 Elev (ft) 101.00 100.75 100.50 100.25 100.00 99.75 0 1 Sunday, Mar 4 2018 = 0.67 = 1.326 = 0.35 = 3.76 = 2.10 = 0.55 = 0.00 = 0.89 Section Reach (ft) Jordan Piaskowy From: Wes Lamarque <WLAMARQUE@fcgov.com> Sent: Wednesday, September 13, 2017 8:38 AM To: Jordan Piaskowy Cc: Noah Nemmers Subject: RE: Kappa Kappa Gamma Drainage Calculations Jordan, This all looks good. Thanks, Wes From: Jordan Piaskowy fmaiIto: Jordan. piaskowy(a baselinecor).com] Sent: Wednesday, September 13, 2017 7:01 AM To: Wes Lamarque Cc: Noah Nemmers Subject: RE: Kappa Kappa Gamma Drainage Calculations Wes, Below is the summary of the detention calculations based on our conversation about the Kappa Kappa Gamma Site. Can you please reply to confirm this is in conformance with Fort Collins Criteria? • Max allowable site release rate = existing impervious area 100-yr runoff + existing pervious area 2-yr runoff • Max allowable pond release rate = Max allowable site release rate — proposed undetained 100-yr runoff • Water quality capture volume = standard equation outlined in the Fort Collins Rational Method Spreadsheet and UDFCD based on area, imperviousness, and drain time. • Additional detention volume triggered by adding impervious area over 5,000 sqft = Utilize the mass balance method within the Fort Collins Rational Method Spreadsheet with the parameters below o Runoff coefficient = 100-yr proposed condition of area draining to the detention pond o Release rate = Max allowable pond release rate as stated above o Area = area draining to the detention pond Thank you for all your help with this. Regards, JORDAN PIASKOWY I Project Engineer, Golden I Baseline Engineering, Planning, & Surveying 11950 Ford Street Golden, CO 804011 Phone: 303.940.9966 x209 I Cell: 720.722.0169 1 Fax: 303.940.9959 1 www.baselinecorp.com Jordan Piaskowy From: Wes Lamarque <WLAMARQUE@fcgov.com> Sent: Monday, October 23, 2017 8:45 AM To: Jordan Piaskowy Cc: Noah Nemmers Subject: RE: Kappa Kappa Gamma Drainage Hi Jordan, All looks good. Thanks, Wes From: Jordan Piaskowy fmaiIto: Jordan. piaskowy0baselinecorD.com] Sent: Thursday, October 19, 2017 4:32 PM To: Wes Lamarque Cc: Noah Nemmers Subject: Kappa Kappa Gamma Drainage Wes, Thank you for taking the time to talk through the comments with me on Tuesday. It seems like we are close to an approved design. I have summarized our conversation below. Please confirm that you agree with it. Comment Number: 2 • The detail will be updated with correct depths and added to the report. Comment Number: 3 • Resolved as -is. • Regular maintain will utilize the boulder step and major maintenance with use a temporary ramp for access. Comment Number: 6 • Plastic pipes will be utilized on site. • 15" RCP pipe will be used for ROW connection. Comment Number: 9 • Drainage easement will be added around the walls of the rain garden. • Easement will be shown in the plat. Comment Number: 10 • Bio-retention calculations will be added to the report. • The filter area requirement will be met by including the entire "rain garden footprint with filter media. • There will be a 6'x26' flat area and the rest will slope 1:5 to the retaining wall bottom. Comment Number: 12 • Outlet structure will be revised. • Remove the underdrain orifice (water quality drain time does not apply). • Top of the inlet structure will match WQCV. • Outlet pipe with restrictor plate will restrict flow to calculated max 100yr outflow rate. 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