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HomeMy WebLinkAboutDrainage Reports - 11/20/1990gevcr-uJ Co�� DRAINAGE REPORT FOR VICTORIAN GABLES PATIO HOMES AT SILVERPLUME P.U.D PREPARED BY STEWART & ASSOCIATES, INC. NOVEMBER 7, 1990 STEWAF<r&AsSOCIATE$ Consulting Engineers and Surveyors November 7, 1990 Mr. Glen Schlueter Storm Drainage Utility City of Fort Collins P 0 Box 580 Fort Collins, CO 80521 Dear Glen: This is the storm drainage report for Victorian Gables Patio Homes at Silverplume P.U.D. The site is at the Southeast corner of Dunbar Avenue and Swallow Road in Section 27, Township 7 North, Range 69 West of the Sixth P.M. It is located in the Spring Creek Drainage Basin. The proposed P.U.D. is a part of The Gables At Silverplume which was designed in 1983. The original P.U.D. contained 12,.33 acres and 4.81 acres were developed. The original storm drainage report was submitted by Merrick & Company and dated March 2, 1983. It divided the site into four sub —basins and provided three detention ponds. Sub —basin A-1 did not have storm water detention. The proposed P.U.D. contains 7.52 acres and has 40 paired housing units in 20 buildings. The original plan had 144 units in 12 buildings. The impervious area has been decreased by 4%. The four original sub —basins are generally remaining the same as the original plan. The only significant change is that original Basin B-2 is being divided into two sub —basins in the proposed plan and each has a detention pond. Basin A-1 is the same as approved on the Drainage Plan for The Gables At Silverplume dated March 17, 1983. Part of the basin flows out the private driveway along the south boundary to the easterly flow line of Dunbar Avenue. The stormwater then flows northerly to an existing inlet at the southeast corner of Dunbar Avenue and Swallow Road. The stormwater is then carried by a storm sewer to the existing detention pond at the corner of Swallow Road and Claremont Drive. The other part of the sub —basin flows down the private drive in the existing Gables At Silverplume to the Dunbar flow line. There is no onsite detention for Basin A-1, it is detained in the Swallow/Claremont Pond. The coefficient of runoff is lowered slightly from 0.58 on the existing plan to 0.56 on the new plan. A copy of the old drainage plan made by Merrick & Company and dated March 7, 1983 showing their drainage basin is included in this report. Also a copy of the new drainage plan is included and the basins are denoted the same. This parcel was previously platted as Cedar Village Fifth Filing. The drainage report for Cedar Village Fifth Filing was prepard by M & I, Consulting Engineers and is dated July 1979. The M & I report designs the pond on Tract "A" at the corner of Swallow Road and Claremeont Drive. The Victorian Gables Patio Homes P.U.D. runoff will decrease due to a lower coefficient of runoff and therefore the pond on Tract "A" as designed will be adequate. James H. Stewart and Associates, Inc. 214 N. Howes Street P.O. Box 429 Ft. Collins, CO80522 303/482-9331 Victorian Gables Patio Homes Drainage Report November 7, 1990 Page 2 Basin A-2 is also the same as approved on the Drainage Plan for The Gables At Silverplume. The rear portion of three paired houses and their rear yards sheet flow northerly through The Gables At Silverplume to the existing detention pond at the corner of Swallow Road and Dunbar Avenue. Basins B-1 and B-2 on the old plan have been divided into three basins, B-1, B-2 and B-3 and each sub -basin has its own detention pond. The discharge from Pond B-1 flows through Pond B-2. A smal area shown as Basin B-4 does not have storm water detention. fZc eta0o is lcsr'IhQ" hisf'otI'G So Dk- The detention pond volumes were calculated using the Mass.Diagram and detain the difference between the two year historic runoff and the 100 year developed runoff. The outflow from the three ponds is metered by using small pipes out to curb chases. Erosion control measures are provided at the outlet points of the three ponds during construction and until the time the seeding of the ponds has been completed. These measures are shown on the drainage plan. The developer shall provide for the clean up of any mud or debris on the existing streets at the end of each work day. The runoff calculations and mass diagrams are included as a part of this report. As stated previously, the Merrick & Company report and the M & I report are attached. If you have any questions regarding the report or drainage plan, please call. Sincerely, Richard A. Rutherford, P.E. & L.S. President lkk enclosures SUBJECT _.VIC_TJJ_L=16L-�@��-S��_'�'LBY_� Hr`i DATE _ZLzz/so 4-- vz�C-..PJ�v/dr --- -------_ SHEETNO.-- '---- _ -- _- -- PROJECT NO.------_-- Az'E,4 =. .7.5zt 'AP � .k, L. P Ex�sr N R�A/J : I /N PEa UL°uJ Ap.�SA 3•.S 4- Ac. 4 7. °� V 0, saq) = O. SB ✓ NE w I- AA) j�Egv:roui A a A = 4rIZ Ate, 4- %Q,Z x 6,54.8) = U •s(o Asl A) rq -.l (/)Ew P U. D• onI,O RossBbg'ova 4 Drke A - 670X 30 _ 0.4G Ac• Z,70 ,Ac,. C= o, S�. t T c_ _ l 6 7 (l, l - O. S6) So o 1�- or 40 '/s `� = 3 o AA / u. Fry• 3-L UzegvDe. U= /•5 L= zS0" T n '3 �+/v 3 4-, 6/1/ v v L=7SOr + 3 M,v. = 3 3 M/,) DEv, Qzyl� = O•SG x /,37x 3•t(, DF_V.. Qioy2 = O.SG x c-•�r,J• v DEv, Q too ye- I Z-J x 'O•S6 x c•F•s. = 7-3 m14. T 3 A4/A), D.. 4 0'13 V - Az- rE/J6 c. 'LTr= 3 m ,v. SUBJECT ,�I�71JL'- ..�1__L2@LtL£.L—:iZ--_. BY_—����C_'_—. DATE_•'t��/-`��' s,! AlE SHEET NO.-- �---- — — — — — — — — — — — PROJECT NO._____--__ i B;As//v A-?--( A) A 0. 72- Ac. C= O. S6 Tc= l'87(/./—O.s30//z. 13 %s 4- i L Tr /•87(/•1-/,zSx/0/AI DES• Q 272 = 0.S6 x 2!2, X 0.17Z a o.89 G.F.S. DES. !Oy/L= O,.S6 X ¢,$ % 0,7Z= 1•`13 L.F.S. . /,.ZSx O,SG. x. Z.z x0,72 i. B AS 1,V 13 _ L (/V Es w -P u b '6 A? � Y� AREA= /.%/ A,,. , Ca0,5(0 V=0.7<t�Src TG ``.. / 87 (� l� O. S&,) Jioo '/I- = Z Z M / ,V , -1- Z M /V = z 9-• Al i.v. L = Ito M iN• "l-' Z M / eJ B xf • /ooyz, �3 DE-v, z _. O.SG x h7 Dev, Q /oyg, _, 01S6 A. 2,9 k /'9/ _ 340 e•FJ. p6v• �(tuy/e. >-:/'LSX..O..S6 x SSx hQ/ _ %,35- c,F,1. i N u T. Tc. 1_ . / 8:7 /. j o. 'soo %z_. IZ 31eM14-). + ?-M"J' .. /,08 !3 ✓ 0.ZOx /,ZSX L9/ = 043 c.�S, j SUBJECT �JLiQ2.�_ELRL_ip Fi'�L.�.j'—�T BY--.j1�A_L__ DATE_ Gs_ /jO SHEETNO._—_5_---- PROJECT NO._ _ TC. IOo �'� - / g�-('/'/ �, }� t /4 An'IAJ. V : , y ; D,Sb x.�/.,9 X Q.qG _ 1,OZc•FJ,c/ i - • i i I D 8 v, D E V;• /ooye c /i 2.$_._0,56 x 6.1 x6•9(- = L• lO c.r,r, - i HT ... T c_ _ il, 87 , /• i3's1 = 3z M1N, B AS- A). ALGA = 1•0( Au. C= O,S6 L= 140 Fr. V=z ' T /Min, O /3 SOO %z = C3 NJ iV, I l M iN. = Zug MiN, Tciooya LP�7Cl,i� �sx',s�) soot/i . /i nn,v, t 1 Al iN, _ /8 m/,V �3 /S D e�, Q zya = . O. SG x /• .�K 7, 0 6 - a, 98 c.,F Jr, DES, �ioylz O:SG xl.*'; 013x .1, oG = l•73 c..F.r. i �.Jr(eiX•'IT X 1.06 = %�-•Dg•G,F,J'�• Nur Tc = /• 43.7 (l• I �o•i) $DD �= 38 M/4/ f i M /u, D•93,/3 Fier, Qzy¢ = 0.20x LZ3X AO(o = v•z� c•Fs. SUBJECT--VJj, Zp„/ /LAd.Z DATE26) ------- SHEETNO.__L2___-- __----. PROJECT NO.__ AS/.V $- 4- A IZC-A = 0 18 q,'•V a Tc c /h 87 �1.1 -D.$�) 1801/Z- C= O.s` 7� - l87(ll- lzsx•sc�lgo�L /oo 13 MIN, 9nlq OeV. Qzyp_ = 0•J6 x Z•ZS x 0.16 = o.Z3 c.F•f.� Dc--� DEV A 0./g = 0.40 a.F.r. Qloo�c c 1. 2SX 0,56 x 7. Z c-, F, J , l/ D67 A)T/0A) Reg, DETB.VTty7 ) / ,e01>OJED �VTLE7 r, t Pou D B-1 11; 17 8 Cu. Fr, // 3G, Z 3 3 C4. rr. 0.48 c.r.I. POND Z3-Z, 54(1a Cu. 97. (.3 ¢8 Cu. FT, Pou C. 67S(o Ca. fir, /3,494 Cu. FT 0.Z4-c,� PoNa B—I Qz 048 C,FS. 1/ = 0.6 z - 0 6 Zx3V 2•z x 4.32 = /0.03 h - 0.}$ - Z✓/U /0.03 - G•% In SE 3 P. V.C, i�oND I3-Z Q: 0.27CC,,c.j.—+0.4g C,F.S. V = A = o.7S _ J4.67 lit UI E 4" P V.C. 7.30 o nJ p f3 C = O. Z (o Il = 0, 6 L4.4 x Z 6s $,1z- SUBJECT V ISr 2 /iI1J-CG'AG..[S_.t�� BY--6./=1 fez--. DATE_iLCcl' `i [J f/yf S�L=1L Lg-=P_C�uJk1 C==_ZFiS1A1_H-I--_ SHEET NO.-- 7 ---.- -- PROJECT NO._-__-_-___ T/MC= MIA.) Z. CfCq Q(CFS.) VOLVAISCF7)3 to 77- 7.zsxo.sbx-i.9�. 9•(0s S790 Zo S.z -" h 3.4- `. 97 B 36 4- 30 4 Z S&3 io, 134- 40 IZ,5z.g 9a 9 z•ss /3, 770 iZp i.4s i.94- l3,9�8 I80 7,4-1 rS,z2g SUBJEC I'�LL>11Jb'.1r41J ©Y_- _,��--_DAIE._._y%7 / ' ��fl1.1LE1�iPi.1l L'lE��--- SHEETNO_ —_--36$-ldJ PROJECT T/me MIN.) `L- C4 CA GFs VOLUME Fri 7•2 /.zsx 0.5a xo.94o. 4 8z 2097 ZU S.L = 0.W 3.48 4-17(o 3o 44,Z Z.81 50s8 40 3..5 Z- 35 5s4,4p 60 Z.ro '/.7 ¢ GZo4- 90 /.Z7 I Z D /. 4S 0- 97 G 9 8 4 180 /. 05 0.70 7 SG D w c 00v 7) J O 4000 Z 000 T/M6 (MiN•) SUBJECT CJ c.. :,�'�7 L,J AIAL—_(_2A_P IL -7L_,AL_. BYUAI E—�,Lz1/2U SHEET NO. ---a---^ -------____ PROJECT NO.__----_--_ TIM E (m)AJ.) Z C4 GA C?(c Frr) VOLUM6�r-r � l0 7• Z /• 2sx 0•s&x J. o& 5.33 3198 zo 5•Z = 0.74- 3. 05 `f loZ0 3o 4•Z 31 11 5598 40 3•s Z • 59 G z /6, (10 IZ 9 0 /• q 4-o 75�0 Zo �¢s !' 1, 07 -770�L- �ao l•os O•78 S4Z4- ry J � O 8 D00 75c 0 L00040o0 r13i .0.Z000QoLEr reAfE Rg1E=o.L�G G.f owAB� VAL RcT QUTL6i /404' 10 10 z0 30 4-O (10 90 izo is 0 -I-iM e (M,.v.) SUBJECT 1 IC TLZ C-i A p/BY-LAt'— --_. DATE lf7lwy------- SHEETNO._1Q----- PROJECT NO.-----__--_ oNf re CVlzg GUT-r6P— CAf-.4G/T-y F,eoAj Z ! ,Sp rl = ,0/ 3/zs� 0 -pA j CAPACv7-y �,. 9 . 44 � 2% I/2_ Q x a.49s x 03107) " ood-) - / 33 G.F.r DVAI 13A e_. CU2..H-CAP4GiT Dv,va4e- PA,iENIEnJT.+rV)Aet A2Ej= /0/5X 31 = 0•77_z_Ac. UAS/N A-% A P-E,4 = 4-12-SAC, BOTH 4' ZS h�... es.s°io 97 Ac� 4./¢ S% C 0MPoi iTE C= /k0.14S) -4 L,56 k0.05S) =0,63 97 Ac. Tc_ 0.(,3) 500 %L / c ZoM/W. V V C�Zy2 0,63 x i e x 4.97 = 5'4- FT%J6c. CORZ G A do i ry T r. M Fir.. 4--/ °/° 2EDUG T/oN F = 0.0 z= V - �Z y " 0. ACLDW {BCC �? _ IZ, pJ C•Ff. 0 /_ 1* y ( r w , i i=a � 1 R•4 9 h,1 4 ,3 �•1 1 � p1 `Y 7•q �iA Y e , �Si Y n yyng •. It cos � f 1 L h( L{ ( ZtY JSJ. � .•i TAWDON AVENUE d� @t 04, q1 a r INV 7391 ^^ ONNECT TO , \ a \ EI(ISTINL INLET So. 6.oeciGLNdeCBS- TO upo / 7{ E ON ' LAP,LI7V .. ,.:.,.SGW nR i www w..,aecu Rr \ \ •7T.2 13. <� JA I l.fn Al \ I. L J tr --- !. r,—_'f I I I I l l l l (LIia . l l l l l l fL1JLL1Lll1llLLL1\, NOTIS: 1. All Y011 COY 110 SET N[S[ OMAN1.11 TO 1[ 1[AIOIIR'D IN ACCORDANCE N llx THE CL TI 01 TORT mLLNS ITAAMAOS 00 SI¢an CATIM. 1. IN OR TO CONSTRUCTION. ALL CNTRACTORS SxALL VISIT EXISTING 11[YAT INS. S. SGCN IANKi -E- CUT ON TN[ NORTH IGNNETT IOLT W EXISTING VTR[ NT0WANT N THE 'MEN Im[ 01 SNULW IUD. EAST 01 IONIC AVENUE. ELEVATION, 5001.03 All [ - 2.67 A.G. 1 h M 5, 101 p[LIpX Or SYMIILY Xpxp \Mp IONIC IY(XU[ REFER TO CONSTRUCTION (INY1XOS wX f L, ALONE I.u.0, VOA n1 pOX OF puxuR AVENUE WIN TO CONSTRUCTION DRAVINGS 101 'Cr DAA nLLAp[ n1T" FILING. S. TIII AIIIOVAL 01 MIII ORAYIMGI.IE IN[ CITY 01 FORT COLLINS HULL NOT RELAY[ THE 0111N IN41MIER 01 RSSIONSIIILITE 101 ERRORS AYOYOR MISSIN$. C 9N INV"0I' K I.,G. iIV� '•T &ECTION A.L PLAN CURB CHASE •DETAIL.• M GiL - c.AA.cITV • 12,ISD CU.If. w w cL . el.D \ nR.. {°b I.W% 1 S'.6' .SRIALT •ROyPY taNTR0. MN - R� °. X( ;NI1tIN:: C04TOUR " N...IN{ D.11N nOYYDARV LINK DER,'.., 01 OMAass' 6e '�'j I ' i -- RHnTIUG LULveRT LYLV\RT �❑1, ' LO;' I. TM[ TYI[, IEEE. LOCATION AYO xUN1LA O[ ALL A,IDIN WOGNOVMO VTIL I IIp AA[ A1110AIMEl .NIA SIGN. ON THE NAYOIpS. IT WALL Ll.'1l4 t`'IIW. IN'[I'{i I . i• !E THE 11 011111LITT OF THE CONTRACTOR TO PERM JUE GISTIAC[ ANO IOGiTOA 01 ALL UNDERGROUND UTILITIES, RIGS( COR[xCI NG CONSTRUCTION. •"'- [ 0. JENSEN ENTERPRISES - - O• per SHEET �_ DRAINAGE PLAN Oop ❑❑❑ �CG( {D THE GABLES AT SILVERPLUME ,:+'.•., oI tN Ni �,r FicALIN.I.Pp - O to 90 60 Iva we / / / •1 / nm Aqb I-j'NNAlt4 BAD iN LIIIE74 � 6Ahlh; A-2 bAhIN A -I a � hNpat tLDW . .. 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IOO YR.-y A,11♦; IINDGK•+1CmNW I/D HCKe GY ALLLrr _ — ___� W•._u Y[y I _ � .A'I- 61RAVING PNV VKPINAy� PLAN. '• T}I A'C �LV6{2 PLUM (• NOMeOWNtKE- A�E.L�IATIoFl 3' 6OHG. !'AN PMAI1,RIP �Z;Al,rcYAIy p��r-k1Es, f K uvcui Iti WIDe "o L <,LL Iq s..-$ ❑❑❑ 00o MERRICK Merrick & Company P.O. Box 975 Fort Collins, CO 80522 March 2, 1983 Mr. Phil Waite City of Fort Collins P.O. Box 580 Fort Collins, CO 80522 RE: The Gables at Silverplume Dear Phil: Based on our discussions and review of the storm drainage analysis for the above referenced project, we are submitting this updated report. The major revision to the drainage analysis is the runoff coefficient used to determine the 2-year historical runoff. The runoff coefficient, C, is the variable of the Rational Method least susceptible to precise determination and requires judgement and understanding on the part of the engineer. Its use in the formula implies a fixed ratio for any given drainage area. In reality this is not the case. The coefficient repre- sents the integrated effects of infiltration, detention storage, evapor ation, retention, flow routing, and interception which all affect the time distribution and peak rate of runoff. Given this consideration, the runoff coefficient has been reduced from 0.3 to 0.2. This results in the following basin characteristics: Area Detention Volume Outflow Rate Basin (acres) (cubic -feet) (cfs) A-2 3.45 17,450 0.83 B-1 2.67 13,487 0.68 B-2 1.96 12,185 0.53 Another revision is the combining of detention for basins B-1 and B-2. This is accomplished by an 8-inch diameter pipe. The 8-inch pipe has a discharge rate of 0.68, therefore the outflow from detention pond B-2 has been increased to 1.21 cfs to accommodate the additional inflow. Should you have comments or questions concerning these amendments, please contact me. Very truly yours, MERRICK & COMPANY Lldy'd G. McLa ghlln Project Manag :jb Merrick & Company: Engineers & Architects • P.O. Box 22026 0 Denver. Colorado 80222 9 Telephone: 303/751-0741 ❑❑a ❑❑ MERRICK SHEET NO.-!!! OF BY��DATE Z-ZB-$3 SUBJECT-���`lEf+'Ptun'/E.3 — ENGINEERS d ARCHITECTS CH BY DATE JOB NO. /'¢'5-"�� loi (3.-Sz5) �• O. 8- c,�s ///iNUTE /UO- i`/P r.F2rOUEI�t� OUiF<O v✓ fTOF/.11E �0 9l ZGG -�9N 8,7Gg / r' Z,Z Or�'St s9710 /G l08 / � E370t/3 7r.:af /p'/JlYcc.�a-��: >// �o C/,i✓. 78 = �S (3��i8,r...^! ?900� /. goax r� �c _ .3Z, 05 rc✓ =o/cu ol%r�cv�.4�/ry c�Y/7-J�p ��.. 7 X Z ❑❑n MGRn'CK BY DATE DATEzzf3 B3 / SUBJECT -S/G ✓�5'�yME SHEET N0. -Z OFs ENGINEERS B ARCHITECTS CHK6. 8Y_ DATE JOB NO./'¢5''464.5 .�uf'-Pam/!=✓�✓ ,B-/ Lr.s r, .5 -•�-c�� ZO-¢ 3, B6 -fl -go 8 r5 9 oil '5/6 95�5 oee 14, 864 3Cn7Z /80 /B !'on you/' B4 = ,.3�✓5O cci. 1n�/ y(•7;�69Oos/i000t G900Xii, )= w-ZO9 i/6-49 /6/ZB Fo/' GA�GU/oy�d G4�lJG/7Y OT /3 �S7 GU.f{. ❑❑o ❑❑rl MERntCK BY.. DATE z Ze 3.:: SUBJECT � �'! y "'r'�%n"%-� SHEET NO. 3 OF= ENGINEERS B ARCHITECTS CH<D. BY DATE JOB NO. �uB-.�3A3ii✓ .Cs Z M,.vyrls /00-yR fiPE4'uENfJ� Oc/fFLOr✓ ,�fp�5-�/(� /O 6, 30.6 3i8 S9g8 /o, /0 4o D %d /8cl> Cp 7�avi 7q = Z70O c,, e;�' Co��ou� 80 �.3�i)�z7ci'� 6i.So > z�opxciso� = 4308 /Z/;�•':5 �:i. ;fit: ❑00 000 MERRICK P.O. Box 975 Fort Collins, Colorado Telephone: 482-3639 February 4, 1983 Mr. Dan R. Jensen d. Jensen Enterprises P.O. Box 1007 Fort Collins, CO 80522 RE: Amendment to Silverplume P.U.D. Dear Dan: This letter report and enclosed drainage plan present drainage informa- tion and recommended improvements for the amendment to Silverplume P.U.D. SITE DESCRIPTION The proposed amended portion of Silverplume P.U.D. is located south of Swallow Road and east of Dunbar Avenue. It consists of Tracts 'D' and 'E' of Silverplume P.U.D. and Lots 45 thru 64, inclusive, of Cedar Village, Fifth Filing. For a vicinity location refer to the enclosed map. DRAINAGE BASIN DESCRIPTION The general topography of the site is comprised of gently rolling features. A moderate ridge line running north and south separates the site into two principal drainage basins. The basin draining west flows into Dunbar Avenue, west on Swallow Road and into the Cedar Village, Fifth Filing detention pond. The basin draining east flows into Swallow Road, thence to Shields Street. DESIGN CRITERIA The amount of stormwater runoff for the individual basins was deter- mined by the rational method. This procedure equates the design flow ; 3 to the total area, amount of rainfall on that area, and a multiplier < that is determined by the physical characteristics of the area under, study. The bulk of the procedures, methods and numerical constants were obtained from the City of Fort Collins Storm Drainage Design Criteria, dated -4 January-1980.- Merrick d Company Engineers d Architects 0 P.O. Boa 22026 • Denver. Colorado 80222 0 Telephone: 303/751-0741 Mr. Dan R. Jensen Page two February 4, 1983 DRAINAGE PLAN Offsite areas have no contributing effect on the drainage plan since the site is located along a moderate ridge line. The site is divided into four sub -basins as shown on the enclosed drain- age plan. Sub -basin A-1 consists of 4.25 acres. It is ��rcrcCO6�'VIU4,A to continue to discharge to Dunbar Avenue as Proposed to allow this area k� ��I �; Collins for Cedar Village, Fifth Filing. The flows eare ythen accumulated the City of t in the Cedar Village, Fifth Filing detention pond located at Swallow Road and Hanover Drive. - _ A _ Sub -basin A-2 consists of 3.45 acres. Stormwater in this basin flows to a detention pond proposed at the intersection of Swallow Road and Dunbar Avenue. The pond has a design capacity of 15,466 cu. ft. to a high water elevation of 5077.I- The discharge is controlled by a 12-inch pipe which has a capacity of 1.32 cfs= The pipe is connected to the existing storm sewer which has been designed to accommodate the anticipated flow. Sub -basin B-1 consists of 2.67 acres. Detention for this basin is located on the south side of Swallow Road in the vicinity of the proposed tennis courts. The pond has a capacity of 11,635 cu. ft. to a high water eleva- tion of 5083.7. The discharge of 1.11 cfs is controlled by an 8-inch pipe which flows to the Swallow Road curb and gutter through a sidewalk chase. Sub -basin B-2 consists of 1.96 acres. Detention is located at the south- west corner of Swallow Road and Bowie Avenue. Pond capacity is 10,663 cu. ft. to a high water elevation of 5080.8. Release is controlled by a 6-inch pipe with a flow rate of 0.86 cfs. The pipe flows to Bowie Avenue by means of a sidewalk chase. CONCLUSIONS This drainage plan will satisfy all hydraulic considerations as well as al equitabletmethodofstormwatermanagement regulations providing this project with both a safe and Should you or others have comments or questions concerning the drainage plan for the amendment to Silverplume P.U.D., please contact me. Very truly yours, MERRICK & COMPANY Lloyd G. McLaughlin Project Manager Enclosures cc: :City of Fort Collins, Storm Drainage Utility ZVFK Architects/Planners LGM:jb c r- � a s • c.•r it I r c I •' � - e Yam• `'`r � � I F :r PROJECT 6 U I a l6 LOCATI Oil . DRAKE RD. CI d _ I`lim D ' .vl �r• � �• �V � .r: e I 15 cc LL r ,'� ♦ a I wFr. U C I r.n.r or:.. ►< J � Se M AI. C. IY r.Cl p:w . c: 0 � � 5 •=C� � . o I 99 J 8 �' • �'_ " e wl.ud N �1 I u a W I N m nd } VICINITY MAP SCALE: 1'■2000' 09% M&I consulting engineers i STORM DRAINAGE FOR CEDAR �5 FORT COLLINS COLORADO . JULY, 1979 jc :::r m- zo'Y•>•�� ?Y #n�.e_T t S'a o }r.rx}i ct iP yy.-y, 1 � ySf5Y '. �Y Y #Y:•r. iV .:w h s5 1 e As Al ' CA r xw1..i .� xx.V,S i �.: iS• .t., ra'C'7' a e`." r JY4.+ STUDY t 'f •4 � .�' Y a. '. Y Y j nr 1 t' VILLAGE FIFTH FILING M&I consulting engineers 4710 South College Ave. Fort Collins, Colorado 80525 Telephone (303) 226-2323 July 25, 1979 Miller Homes, Inc. P.O. Box 1007 Fort Collins, CO 80522 ATTN: Bruce Miller Dear Bruce: Presented herein is a storm drainage report for Cedar Village Filing No. 5, located in the City of Fort Collins. This report conforms to both the subdivision regulations of the City of Fort Collins and the Federal Housing Authority. All calculations pertaining to this report are available upon request at our office. Please feel free to contact us with your questions or comments. Very truly yours, M S I, INC. Stan A. Myers .E.-L.S. Enclosures TABLE OF CONTENTS Page No. I. Introduction . . . . . . . . . . . . . . . . . . 1 II. Study Area . . . . . . . . . . . . . . . . . . . 1 III. Existing Storm Drainage . . . . . . . . . . . . . 1 IV. Design Criteria and Requirements . . . . . . . . 2-3 V. Drainage Plan. . . . . . . . . . . ... . . . . . 3-4 VI. Conclusions and Recommendations. . . . . . . . . 5 Exhibit. No. 1 "Vicinity Map" Exhibit No. 2 "Design Flows" '` F W I. INTRODUCTION WThe purpose of this report is to present the developer with a proposed series of improvements which will provide for proper management of storm water runoff from both the Cedar Village Fifth Filing itself and adjacent contributing basins. The scope of this report involves an analysis of the storm drainage characteristics of this property in both its historical and improved conditions, consisting of the following items: 1) Established rainfall intensity duration curves for the City of Fort Collins. 2) Storm runoff quantities and their general direction of flow. 3) The size and slope of storm drains required. 4) Size and location of detention ponds and culverts. II. STUDY AREA The area on which this study is focused is Cedar Village Filing No. 5 and its contributary basins. This subdivision is located in the southwest portion of Fort Collins, just west of Rocky Mountain High School. Exhi— bit No. 1 displays Cedar Village Filing No. 5's geographic location. III. EXISTING STORM DRAINAGE FACILITIES Cedar Village Filing No. 5 is bounded on the north by Cedar Village Fil— ings No. 3 and No. 4. These subdivisions are fully developed. Drainage is facilitated in them predominantly by surface flow, however, a 21" RCP has been .stubbed out at the subdivision boundary in Hanover Drive to pro— vide for future anticipated flows. The general topography of the area is comprised of gently rolling features, basically sloping from south to north. - 1 — IV. DESIGN CRITERIA AND REQUIREMENTS The initial and the major drainage system make up the storm runoff drain- age system for an urban area. The initial drainage system should be designed to accommodate the runoff from a 2-year storm by utilizing the maximum capacity of the streets, overland swales and, if necessary, underground conduits. The major drainage system must be designed to han- dle a 100-year storm without extensive property damage or loss of life. Areas which may be susceptible to flooding must be examined. For pur- poses of the major storm analysis, it is assumed that the storm sewer has been blocked and rendered ineffectual. Floor elevations should be set to allow proper drainage between and around these houses without flooding. (See Exhibit No. 2). The City of Fort Collins requires an improved site to limit its runoff to the amount resulting from a 2-year frequency storm occurring while the site is in to design its natural state. To accomplish this, it is usally detention necessary a pond with a total storage capacity of the maximum difference between the 100-year storm runoff from the developed area and the 2-year historical flow. An outlet structure is designed to limit the flow to the 2-year historical runoff value. The amount of storm water runoff for the area, individual basins and streets was determined by the rational method. This procedure equates the design peak flow to the total area, amount of rainfall on that area, and a multiplier that is determined by the physical characteristics of the area under study. The rational method is commonly employed in the design of borrow ditches and storm sewer systems. The bulk of the proce- dures, methods and numerical constants were obtained from the Urban Storm Drainage Criteria Manual, published by the Denver Regional Council of Governments. The rainfall intensity duration curves used in this report were developed by the City of Fort Collins Engineering Department. - 2 - The ponding elevations, capacities of the channels and piping were determined by Manning's Formula, which equates a constant, a roughness factor, the area of the channel or pipe, the hydraulic radius and the slope, to the capacity of the channel or pipe. IV. DRAINAGE PLAN The approach taken to develop a drainage plan for Cedar Village Filing No. 5 was effected considerably by the runoff flowing both to and from offsite areas. The central system'of the project will consist of a piping system to be located in West Swallow Road and a detention pond to be situated in Tract "A" (See Exhibit No. 2). The pipe system was sized to handle the 2-year developed flows. The storage capacity of the pond was determined by the "Mass Diagram" procedure. Each of these designs, however, was modified due to offsite runoff considerations. One of the offsite considerations, involved the four streets at the north subdivision boundary, which drain into Cedar Village Filings No. 3 and No. 4. Although each of these streets drain relatively small areas the difference between 2-year historic flows and 100-year developed flows accumlates to a total of 10.8 cfs. This difference, of course, must be compensated for by reducing the outfall flow allowed from the proposed detention pond. However, runoff is also flowing into the subdivision from the west and east ends of Swallow Road also increases the outfall flow allowed from the proposed pond. In this case the difference between the 2-year historic flows and 100-year developed flows amounts to 8.67 cfs. This means, of course that the design outfall from the pond needs to be reduced only by 2.13 cfs. It should be noted that runoff quanti- ties flowing out of Cedar Village Filing No. 5 from Haywood Place, Yose- mite Drive and Tawson Avenue have no affect on the above calculations because they will be contained in another separate drainage system, which will be developed in the future. - 3 - EM The runoff contributed by Basins 2 and 3 is to be collected entirely by curb inlets at the intersection of Dunbar Avenue and Swallow Road. This is proposed in order to avoid valley pans across this principal intersec— tion. These inlets have also been sized to handle the runoff flowing into the subdivision from the proposed' Silverplume Development located immediately east of Cedar Village Filing No. 5. The runoff from Basin 1 will also be collected entirely at the intersection of Dunbar Avenue and Swallow Road from this point, because of flowline and slope considera— tions the accumlated runoff will be piped directly to the pond proposed in tract "A". Another small storm sewer located just south of the pro— posed pond will facilitate the drainage of the sump area in Swallow Road into which Basins 4 and 5 drain. The detention pond in Tract "A" will have a storage capacity of 1.76 acre—feet. This allows for over 1.0 foot of freeboard. The pond will have an outlet of 4.0 cfs. This figure reflects a reduction of 2.13 cfs., which was discussed earlier. The pond will outlet into the ifexisting 21" RCP located in Hanover Drive which eventually flows into Spring Creek. A spillway located in the northwest corner of the pond ifallows for control of outfall should the pond overtop. Another major consideration was the runoff generated by the proposed a� Rossborough Subdivision located just south of Cedar Village Filing No. 5. Considerable analysis and investigation revealed that due to problems with invert elevations and minimum slopes as well as cost considerations no runoff from Rossborough could be handled through the subdivision. It is recommended that two year and 100 year flows from Rossborough be piped west into the proposed_by_pass ditch, which will run north along the west 1/16th line of Section 27. ifDuring a major (100—year frequency) storm, there are only two areas sus— ceptible to flooding. Exhibit No. 2 illustrates these two points, the areas covered, and the maximum depth, as measured at the flowline of the gutter. In all three cases no damage would occur to homes in the imme— diate area. — 4 — VI. CONCLUSIONS AND RECOMMENDATIONS This drainage design will satisfy all hydraulic considerations as well as governmental regulations in providing this future community with both a safe and equitable solution to the problem of handling storm water run- off. The following is recommended: 1) Storm water runoff should be routed as shown on Exhibit No. 2. 2) All drainage facilities and detention ponds should be constructed as shown on Exhibit No. 2. 3) The Federal Housing Administration minimum requirements be maintained on overlot grading and street design. - 5 - �GG�G OAD RPLUM OC I- • _ FUTURE y ^��--G^ W I ' ` y1 - ]SWALLOW - CEDAR PR OSED -VILLAGE SUBDIV SION1 FILING NO.[_ L• E TOO T.. atlC VICINITY MAP NO SCALE EXHIBIT . CEDAR VILLAGE FILING N0.5 EXHIBIT NO. 2 DESIGN FLOWS FOR 2 YR. AND 100 YR. FREQUENCY STORMS 5070 W „ } _ _ o „ CEDAR VILLAGE F1L.INGS N4.4 a N43_�� _ w ' w 0 Z u r � N O u a: m'ZI^.-TRACT,�A:� Q�' O 0 00 o c DETENTION POND ,y0� y0� y0� a o% o �o __. OUTLET ! 1 CAP. • 1.76 AC.FT. ..'3 ' p ao<f._ .: .... HIGH WATER I Z ELEV.- 00 FP fr1 Z i 5082 00 YR. PONDING LEV \� AX. DEPTH TO E=0. 6' t o� 9 •B �� \r \ i 8Ati N 5 v A14=1.89.� yc BASIN 3 0 p2•/s I �F AREA=0.46 AC. 90 seta y o� 90� P 5078 0 /p0i9, J> �\ OOO ............. PROPOSED 0 SI LVERPLUME A b:• DEVELOPMENT T �y ✓ � z 100 YR. PONDING LEVEL MAX. DEPTH TO IL z 0.42' R -y LEGEND W 5080 DESIGNATES DRAINAGE BASIN a INDICATES DIRECTION a QUANTITY OF FLOW IN CUBIC ASI -- ..........FEET PER SECOND-"C.F.S." I - `'AREA' :60 AC. 0 . 3 5082 c CITY OFFORT COLLINS STANDARD CATCH BASIN ENUE _ o CITY OF FORT COLLINS 5084 STANDARD 6' VALLEY PAN STORM 'SEWER PIPE I S/„c y SUBJECT _I�ILLO�JA tL E L_ �S BY__ —a -As— _. DAIE�y_'�' SHEETNO.___—_--_ — _��.):—DSr___—_------�__—. 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LINES) Soo .OS c IVEN: ! 1.01 cr) 70 n a 0.3.23 U 0 LL 2o FIND: o • 2.0 crs _----_ to Z a ' 0 400 W INSTRUCTIONS Vr OI 300 Q .o, I. conx[cr [/n Ro10 WITH xaP[ uI Q .py Z K161-1 100 90 60 70 60 50 cE K-1 r From BP - 2.0 A. 6o 70 60 [50 W 40 2 v 1.30 -_ R .NO <OMNECr DISCHARGE l01 AT. 03 .008 D[rrN In, rNE![ rr0 ux[! uusr U .02 Q 007 INTERSECT AT TUR.;.. LINE FOR COMPLETE sOLUF10M. Q .01 " _006 2. r0A !HALLOW .005 v-IN.rEO cNAwNEL O AS SHOWN USE NOYOCIAIx NET. t Y .004 W a rJ 0 .003 a. TO D[TE..UI( on .... GE 0, IN VP Pw nON or cHAwxu .AIIIND NO'. .: DETERMINE DEPTH J FOR TOTAL DISCHARGE 10 .002 ENTIRE SECTION a. THEN USE NOMOGRAPH r0 DETERMINE 0 N SECTION A FOR OEPT. J.J-(I) r •.TO OErER YIw[ DISC NA RG! ♦ J 1w CG.I.S.T1 SEC r10N �- J a FOLLOW INSTROCIION ) I e " ZA .001 r0 De'AlA .nc.IIZE "A SECTOR A AT SS..ED 't.IJ'il 9Err. J; olu1N 0. roA al9IS RATIO E. ... DEPT. i TUE. 9, . 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