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HomeMy WebLinkAboutDrainage Reports - 11/08/1990STORM DRAINAGE REPORT FOR BETHEL BAPTIST CHURCH PREPARED BY STEWART & ASSOCIATES. INC. NOVEMBER 8. 1990 The Bethel Baptist Church site is located on the west side of South Taft Hill Road between Orchard Place and West Plum Street. The site is not in a platted subdiv�s_ion nr P.U.D., and the_zoni.ngs RMP. The church is in the "use by right' category The area of the sib -is 122,UUU square teet. The present development of the site consists of a church building and a gravel parking lot on the southerly 80,000 square feet, and an unused area covered with vegetation on the northerly 42,000 square feet. The "West Plum Drainage Channel" passes through the site in an existing ditch running from west to east approximately 140 feet south of Orchard Place. A study of the "West Plum Drainage Channel" is presently being prepared by Resource Consultants. The study proposes that there shall not be detention required on the Bethel Baptist Church site. The study also provides flow quantities through the site, which we have used to calculate depths of flow through the existing ditch. These calculations are shown on computation sheet 5 of this report. We plan to not do any regrading of the ditch for this repaving project. The calculations on sheet 5 show that the 100 year flow quantity will pass through the site with a maximum depth in the parking lot of 1.2 feet. The lowest opening in the building is 1.0 feet above the 100 year high water line. Future develpment on the north 42,000 feet of the site, lying north of the drainage ditch, shall require additional design of the drainageway, which will probably entail enlargement of the drainage ditch. There is an existing 12 inch concrete low flow pipe under the existing.ditch, which we propose not to disturb at this time. Computation sheet 4 of this report shows the existing runoff quantities from the north 42,000 square feet of the site. We have calculated runoff quantities from the south 80,000 square feet of the site, and these quantities are shown on computation sheet 3 of this report. The quantities are calculated for both the existing site and for the developed site.. We propose to let the runoff from the paved parking lot outflow directly into the existing drainage ditch. The outfall will be through openings in the curb and then along concrete pans to the flow line of the ditch. We plan to prevent erosion of the ditch by installing rip rap where flows leave the concrete pans. Runoff quantities which will be carried by the pans, and which is generated by three sub -basins on the site, are calculated on sheet 4 of this report. The "West Plum Drainage Channel" lying directly west of the Bethel Baptist site passes through an apartment house development, and is constructed as an open channel. This open channel enters the west side of the Bethel Baptist site, passes through the existing drain ditch, and then exits under South 1 Bethel Baptist Church November 29, 1990 Taft Hill Road through two 2.75' X 5.50' eliptical pipes. On computation sheet 6 of this report, we have calculated the capacity of these two pipes, and it appears the pipe capacity is fairly close to the maximum 100 year flow, so there may not be overtopping of South Taft Hill Road. If there is overtopping, it will not cause any problems to the Bethel Baptist site, since the street grade is approximately three feet below the lowest building openings. We have included a plan of the proposed parking lot paving at sheet 7 of this report. We have also included copies of a portion of the West Plum Street Drainage Basin Study, at sheets 8, 9, and 10 of this report. These copies show a plan of the site along with peak flows and water surface elevations. Phillip Robinson, P.E. & L.S. roOeICj\STER�°.O,r�a.����. e •. • •, o _ ,0. e 450 ` 00 :eA 5: o,: :: '� P�I ,,','�/Fl19tlQG4 ♦ 2 COMPUTATIONS ---..- Stewart & Associates, Inc. - 214 N.. Howes. St.. • Ft. Collins, CO 8052.1 (303) 482-9331 By: PIZK Date // Client:— f eAs-I LLczg7'ISf ChurGA Sheet No. •3 of 10 Chkd By: Date Project: 833 s- 7-a11- 1181 TKO Subject /9 o W r 4! n F�(>n%0F. i FIT O M! I --' j -1 -- ;N —� -i - _ . l•..837 .ac. _ CQlCIi�aTI.U�11.iOT_.�GG. 0 _. : %arc r a!✓ jel.. PI ; - - -- __Q 1-7 _ - -- - - GO pas/�e - - o s a O .�0 i I ' �¢ 10, '6 Tc _ j...� L. 56 3 0 q Jy3 _.. - I I i --- -- — - .. Qio-_.i..Cl r. .O._.S�G�i 25 i G I3,.3_ ��193- - - — - 3!.9- i �SI. � TOK1CFIW I )�UNoIrF; . tTO�► -. ).'8 7-� a.u. ' -- p_ - -- I f /-�a-e� ! .�IIdS.. !�' per.. �-.� : � _... �l•-��� I I � -� � i ! i r4e- rr s 4?17 ! i i II � _ C't1• II, --I I�` DEV LO D' FLOws ! z_I �l._�_��� -.7� ��.__!-.)�. 8 �� L !c is I i I j � i. . ' • i ' i 1 I , I � I � � i COMPUTATIONS Stewart & Associates, Inc. 214 N. Howes St. Ft. Collins, CO 80521 (303) 482-9331 By: PI'M Date 11) 71 YO Client: SPI 6 el Cti UrCg� Sheet No. 4— of 0 Chkd By: — Date— Project: 033 5- T,:aT4-. 11m Rd-, Subject9vndA Ft-og-_ Ondeve)qped A/eg-A Portion of _54e anL 4-am Par-k674IU)" IF opt0 5 �111 0.: 1 ON 3f RUNOFF FROM J3;As1w1 W'Q. il C 1. -� i � = i I V, ( ) 6 1 0.2 ); + (") 34 0 aiup KvNgJFr- :FRom 13, 10.142 Z7 OW1.0. + 0.5 q 0. Arexi- I I Tr L-73 ,� 'Ii gq 6 43- '57:1) !.Z� 3 S- _T a it, e IA I C 0- 7) 00 CC- 5 a A 5 1r;um0Fr_ :FKa�v 6 0 06 1 Te- I a 0 On. 0 4-ma. 0 rig bo z A10 r< TN 4-2_qg�0 S-F, 170" be c, d?,!diver Pei tAis 4 4 13 W 35( -2-4) :03 0. 2- COMPUTATIONS Stewart & Associates, Inc. 214 N. Howes St. Ft. Collins, CO 80521 (303) 482-9331 By: 271 R Date.-)I):21 20 Client: 3e+6el 13cipb-s-E GLrC4 Sheet No. 57 of J 0 T_ T_ Chkd By: — Date— Project: Fd Subject — V\le--s U m (:5 �7'pl n 4 e, r 0 o ri U (7 LA J=Ju,jS Iq-7_0 �Jes.4-10+1 ! -rcT4- 6di rl 0 00'i T4 -v I q 10 1:10 C C_ SrS; P01-t0 V1 AC—. 4 r� F rOVS A!-T V 57 r t4AP ,57 SITE cz c; c�-4-,e J L/ 17,614 pill .2AII rz * 131" )ZS te5 Z10 _7777-:I 0 Z51 zp N va, f);-5- 5.3)(1 .15 a r I a! I v T tH rz 5— (fA41'4NA;E L A z 3 0 60 0. -4 0 7 Al tZ V. FLaL �)A�CAIAIGL ell L/ ; I (e) Z. sPf F L y-1 0 :/c4T PEAK i 13� 1/ more Aan01 1)(2. .7 rewired) vim! c;- C'� J. i 1�4v 1• 4- 5 ro 0 x r" ��e' iz; -peel,+ L OTP 0 S) e-, bvl, ins,willbe COMPUTATIONS Stewart & Associates, Inc. 214 N. Howes St. Ft. Collins, CO 80521 (303) 482-9331 By: Date Client: ge-A e 1 45 q ;2LS461 VtC S Sheet No. of 10 Chkd By: Date- Project:- 8.3 3 -5-1 9; ( 7—<oo, Subject 6? C ) ):2 of 6x is �i e,-):5 oncel- -:L 7-oll- M-0 Rd, YN I I III m�l sP� I O^ N^ro / /y!/ o I eE:, oo 0Jy"or" l; '" Q;X V ,te e R/-*)SIN 0,4Z TIC i% h0.5i p0 n 00/ 0 1• � 0 �— � r 0.57 i}c �+ v/•IDOw WELLS G` ELM(71.5) G I LZ t--L�Qjr L = —LY I II Nap* J46 ooMy xlh G4uga 13Asl 3 , , FLOOR t7Z.35co I } , I/ I eHV 5G3•zo4 'e WALK I 9 I I I �•Ih L•• Zb,ob ,� y3.i/h � � . . •• .• - -- = =--- -:. �.:�avj. II , 7 6 w==-- 4,D I. so' Z � I/ z D•�\ ul 1r GB V' " .Z N � �toB.C.) y u i L „ 0'1 e .0) / V 0� N U I �v N I a.= EXISTING INLET 00X FOR LOV FLOW vIPE I I I ��- �0 I 1-2 WIDE coNc. PAN (• C T. I I !O 5F''/2 RIPRAP I�- V f3E DDIN(� 1iIjEX15T. /zLOw FLOI✓FIPE FLOW LINE OF: CR1caIN DITCH 100 s F ' /zRIPRAm o ON C, 0 EL OEPOINO AVID! CONC:PAN �- / I•I Q2 = /.4-G7-f. C_ %�i Y .I .i= X M I• j 10�7'YEAR'LOOD= �✓p7�l�SOfzFHcJ /5. x Y(ce.zl cpd N L. 5 Z PA" 2 VICE CONC. PAN 10 S.F. - 12' RIPRAP /'' Z O � �� ON. (•'• GRAVEL CSE DDINF�/ (JZ fdf 0.7 -Gdlo '_ EXISTING RIP RAp' i ,"VcR PIPES t (LI. 07) {�// I ' EXISTING 2- 2.751-S.SO' ELIPTICAL CONC. PIPES III S�CT10N LWELWE mW Q J A[ Q 11 II II II II II I I - II II I II II II II II I II II II II II II II II II II II II II II II II II II II II • � sac � � '�''"� �•.�a ,J.}. *' '��!'.'� ♦r �f � a f l f or, n Reach 3 i Reach 2 _ E-iiI:I.�i1it � • ��/���=�� �� �� ��ii•���� wit t N E 1 C J � O £� 0 \\` C O J �- N _ C O T O O a c o c N o � o, c c N — d N N d 0 X ❑ 0 w { r 0 i W <o�LD ix 4(p V ❑G m< Z Z C < W C 0<r-Yt` Z•^ U(g��C L` W Z f� 0 ->U• <C- ZWL) < � w � W ❑ ^ c C Ur 0 C W ❑ - C Z ` © J < Y LLJW C7 < c7Cw❑o�❑coWw 2 z<N0� 0� � =~zZL c UJ ��0ZIL V) WiO�i" c OOW w~z0�O0<�, 0 z W � Z � Co Q J C }_ Z O c' W U N � Cr1 e Q •0• O c c3 NW LL n C7 0 � C IL ¢ U F � C o w s 46.00 44+00 42+00 40+00 38+00 36+00 34+00 32-00 30-00 28-00 26-UU 41+-UU GG•UU GU+UU 8 Table 2. Computed Peak Flows at Points within the West Plum Basin (Fully Developed Conditions) Point Location Con% 2-yr 5-yr 10-yr 25-yr 100-yr Elem. A Overland Trail 20 9 12 14 15 17 B Proposed Scenic 22 2 4 15 24 47 Views Detention C _ Kimbal Detention 24 29 51 67 86 127 i D Rocky Road 26 28 28 34 t 70 121 E Pear Street 28 38 52 60 a5 154 F Timber Lane 30 34 34 36 62 183 G Tyler Street 31 47 62 71 82 171 H Ponderosa Drive 32 57 82 100 123 255 I W. of Sun Ray Apts. 34 64 98 121 154 256 I Taft Hill Road 35 72 117 147 198 288 K Orchard Pl. 29 9 22 32 45 74 _ (North Tributary) L Glenmore Dr.(channel) 38 82 130 160 202 309 M Skyline Drive 39 108 183 233 306 455 1� The locations of these points are shown on Figure 3. The hydrologic analysis shows peak flows along the major drainageway for the 100- year event to range from 17 cfs at Overland Trail to 455 cfs at Skyline Drive. Using the peak flows, the flood water levels can be determined through hydraulic analysis and are presented in the next section. Hydraulic Analysis Investigation of the extent of flooding was conducted using the flows computer during the hydrologic analysis. Cross sections of the channel and overbanks were developed from aerial mapping and field surveys as discussed previously in this report. Utilizing this information, the U. S. Army Corps of Engineers HEC-2 Water Surface Profile program was used to determine the extent of flooding. The modeling effort was supplemented with manual computations, as needed, to prepare the floodplain map shown in Plates 1, 2, and 3 for the four reaches described earlier. Also depicted on the plan views in these plates are the existing structures, minimum channel elevations, and 100-year water surface profile. The discharges used in the modeling process are shown in Table 2 and a discharge profile is shown in Figure 4. Table 3 summarizes the flood elevations that were computed 9 of 10 i Table 3 Water Surface Elevations Section Station Channel - 2 year- - 5 year- - 10 year - Number Elm Flow W.S.E Flow W.S.E Flow W.S.E (Ref. Plates 1-3) (ft.) (cfs) (ft.) (cfs) (ft.) (cfs) (ft.) - 25 year - Flow W.S.E (cfs) (ft.) - 100 year - Flow W.S.E. (cfs) (ft.) 1 170 5049.60 110 5051.47 185 5052.00 235 505228 305 5052.80 455 5054.93 199 5049.60 110 505150 185 5052.02 235 505231 305 5052.81 455 5054.83 2 200 5055.45 110 5055.65 185 5055.77 235 5055.82 305 5055.87 455 5055.96 3 230 5055.45 110 5055.74 18S 5055.88 235 5055.94 305 5056.01 455 5056.11 4 290 505450 110 5055.76 185 5055.89 235 5055.92 305 5055.92 379 5056.00 364 5056.00 110 505634 185 5056.60 235 5056.71 305 5056.93 455 5057.04 5 365 5050.45 110 5056.41 185 5056.69 235 5056.80 305 5056.91 455 5057.06 6 410 5051.40 110 5056AI 185 5056.67 235 5056.76 305 5056.93 455 5057.11 475 505350 110 505652 185 5056.90 235 5057.09 305 505733 455 5057.88 7 476 5051.80 110 505652 185 5056.90 235 5057.09 305 5057.33 455 5057.98 8 800 5054.00 110 S05653 185 5056.94 235 5057.15 305 5057.41 455 5057.97 9 1050 5055.80 110 5057.78 18S 5057.88 235 5057.87 305 5057.94 455 5058.28 10 1270 5057.00 110 505850 185 5058.63 235 5058.74 305 5058.82 455 5058.88 11 1490 505&00 85 5058.87 130 5059.03 160 5059.10 205 5059.19 310 50S9.39 12 1675 5059.10 85 5060.87 130 5061.29 160 5061.47 205 5061.67 310 5061.91 13 1850 5061.00 8S 5062.66 130 5062.98 160 5063.14 205 5063.33 310 5063.33 14 1910 5061.66 85 5062.94 130 5063.24 160 5063.40 205 5063.61 310 5064.05 1924 5061?6 85 5062.95 130 506327 160 5063.42 205 5063.64 310 5064.09 15 1925 5060.17 85 5062.77 130 5062.99 160 5063.28 205 5063.63 310 5064.48 2003 506027 85 506350 130 5064.94 160 5063.87 205 5064.29 310 50-66.83 16 2006 5060.17 85 5063.91 130 5065.13 160 5064.91 205 5065.34 310 506721 17 2055 5065.60 8S 5067.44 130 5068.19 160 5068.43 205 5068.62 310 5068.81 18 2400 5065.90 65 5068.87 100 506931 120 5069.44 155 5069.62 255 5069.98 19 2510 506630 65 5068.93 100 506936 120 506950 155 5069.68 255 5070.03 20 2700 5067.60 65 506925 100 5069.74 120 5069.93 155 5070.19 255 5070.71 21 3000 5072.40 65 507332 100 5073.42 120 5073.50 155 507359 255 5073.89 22 3300 5075.00 65 5075.68 100 507533 120 5075.89 155 5076.00 255 5076.18 23 3445 5075.80 65 5077.98 100 507837 120 507856 155 5078.87 255 5079.62 3499 5076.10 65 5078.81 100 507930 120 507953 155 5079.87 255 5080.60 24 3500 5081.48 65 5081.61 100 5081.75 120 5081.79 155 5081.96 255 5081.99 3550 5081.48 65 5081.71 100 5081.89 120 5081.95 155 5082.03 255 5082.19 25 3551 5077.01 57 5081.69 82 5081.87 100 5081.92 123 5082.01 255 5082.14 3600 5078.00 57 5081.71 82 5081.88 100 5081.92 123 5081.98 255 5081.76 3690 5079.15 57 5081.78 82 5082.01 100 5082.11 123 5082.25 255 5082.92 26 3685 508150 57 5082.15 72 508223 86 5W2.28 103 5082.34 255 5082.92 27 3775 508450 57 5085.19 72 508539 86 508551 103 5095.64 255 509632 28 3850 5086.00 57 5086.18 72 508624 86 508630 103 508636 255 5086.78 10 or- 10