Loading...
HomeMy WebLinkAboutDrainage Reports - 10/01/1979CORNF-11 CONSUITiNCI COMPANY po. Im 106 loRiWbrrcd(wA&80522 14cof: (M)482-6650= MANA4WNIAWNEERiNq ALBERTSONS SITE CREGER PLAZA LOTS 1-4 DRAINAGE REPORT No Text I. SCOPE The purpose of this report is to present the City of Fort Collins Planning and Engineering Departments with support data necessary to evaluate the Albertsons final site plan. As submitted, the final site plan provides feasible and adequate engineering solutions to storm runoff -related problems for Lots 1-4 of Creger Plaza. Specific items addressed are: 1. Extension of Mason Street interceptor sewer from the low point in Mason Street to the Mason Street - Creger Drive intersection. 2. Detention design sufficient to deal with the 100-year storm. DESCRIPTION OF DEVELOPMENT Creger Plaza is a 20-acre commercial subdivision located at the southwest corner of the intersection of Horsetooth Road and College Avenue, Larimer County, Colorado. The Albertsons site, Lots 1 through 4, comprise the extreme northern portion of Creger Plaza. The site has an area of 9.13 acres of which only 0.89 historically drain to the south. This historic ridge line was defined as the northern boundary of the proposed Mason Street Storm Sewer Inter- ceptor Improvement Dis.trict. The remaining area historically drains.to Larimer County Canal #2. See Appendix, page 1 for further basin information. -2- Ill. METHODS In general, the storm drainage analysis was completed using the Preliminary Draft, Storm Drainage Design Criteria for the City.of Fort Collins, The Rational Method was used to determine peak flows as the site is less than 10 acres. Specifically, a 2-year historic storm was used as the unit allowable release of the northern portion, while the design flow of the Mason . Street Interceptor. controls the allowable release of the southern portion (see Appendix, page 1). Required detention was calculated using the accumulated runoff method (see Appendix, page 2). Actual detention was measured from the final site grading plan using the equations from Section 10.1 (see Appendix, page 3). In addition, the hydraulic grade line and half -full velocity were calculated for the storm sewer extension (see Appendix, pages 4-6). As most flow reaches the detention areas as sheet flow, no gutter flow calculations were performed except for where the flow was con- centrated by a cut through parking separators (see Appendix, page 7). -3- IV. HYDROLOGIC -HYDRAULIC INVESTIGATION Major Storm Drainage basins for the 100-year storm are shown on the final site grading and drainage plan. This basin boundary differs from the historic significantly. This change was incorporated as a result of meetings with representatives of the Larimer County Canal No. 2 Board of Directors. The new boundary decreases by.a third the area of.the site contributing runoff to the canal. z This change also affects the improvement district that is presently being formed for the Mason Street storm sewer. Harry Cornell from this office, and Don Deagle of the City of Fort Collins are presently coordinating that aspect of the drainage. The 100-year storm is contained in two detention ponds shown on the grading and drainage plan. The northern pond is released through an oriface plate and culvert. .Flow then passes through a silt filter before entering the irrigation canal. The southern detention is discharged into the extension of Mason Street Interceptor with.the final discharge point being Mail,Creek. Because the hydraulic grade- line is slightly higher than the detention water surface at the site, an oriface plate -is not required for the southern pond. Minor Storm The parking pattern delivers water to the detention ponds as sheet flow with little flow concentrated at gutter line. Also, little -4- overlot flow contributes to street gutter flow. Furthermore, the basins defined for the 100-year storm are identical to the basins for the 10-year storm. Therefore, we see no need for further analysis of a minor storm. Storm Sewer Extension The proposed design for the extension is shown on the Plan and Profile sheet submitted with the site plan. Several points need to be made about this design. First, the pipe size and ali n Street extension plans presently under review by the Ciry Fnninaorinn Department. We will incorporate .the new design at such time as we address other comments from the Engineering staff. Second, the change in the proposed improvement district boundaries has already been addressed. Finally, the hydraulic capacity of the extension is .shown in the hydraulic gradeline calculations (see Appendix, pages 5-6). Assumptions for this calculation include taking the head elevation for manhole 16 from previous design. It is noted that the total flow in the interceptor will be increased by 1.5 cfs. This ranges from 9 percent to 3 percent of total flow in the pipe. It is our opinion that this increase is not sufficient to warrant a redesign of the proposed interceptor.. -5- V. CONCLUSIONS Details and final plans for handling drainage -related problems are shown on the two -sheet plan set from this office submitted with the final site plan. It is our opinion that this design safely handles the 100-year storm and safely conveys water off -site. We hope this report has been useful for the reviewing agencies in their processing of these plans. i K`�SJ�o�ocztc.�t� CALc. F6 P- LR,'F- o�S s trtr . SLcc1-c.� K np.siN nn ,4 RY f _-.1 t( s� W~ C1kly/ u tt�s[aEz�c C-0NpX710NS CI$n'fs tTo dt, of ST-PV F-M) 0.8�1 1� cLt �DED �N GLIhSo*i sT- cv c i�yZ-� cArt a L ttz a, cs- -rc c 3S Q Q -- 1. 3 � � 2, O• �6 crsS �/.aC -iOr' • zy r- all,... h:s�'o�'ic 4lgr'i'ltie.✓'� }�cts��� 'j�ma�'.oPcCJ� core, t�ov�s 'Zo�G •. ti}� =�., Gam' o '.©� �Or. ��©�n ' So'siv.s 2 0.S S6ow�r.} it slc�tc� G1po�c 5rno s�.hS Q7lhr�0 1 joc. '�"ec�"c'.c'�z- vU ��-h �oWN Lot V- v\,� �hcsc Z R�.l c.u•sc Rct��s = o . Z6 � s ��- t`(•o rt� Scams ; h 1-So ...�� �5c�s 1 +�f /. •Ci c�sc� . G h aCC S o� v� C'iC i S C-✓��l V01 C- "• /V\caso /� Sim. �w•F�. rc��t'o r . T�0.5� h CNO•'t-� - �•%.QA-, �oK�'v L�oc1 w 7 1. 2 6 P-S P (A PA LAl L- A,-r � VUAN(OF F eALC LA LIST tC> N.5, DF Co" ttAs (CD -yt^ C:) . c .-Fl f^Ti Cm I M t,t o T- F- 'o• 5- CAL akcc.tq�\ V� S rt,>Ir V,\. (S+ -7 `t 2-5 A-ST' b t-A F- U, V--'TT- ti -T. (O'V-k -PC=) ND � LA PAV- GPI L- C.-CA L- A t kO � fLlD ov "k CD.176 3.CL3 -3 6.Sc4 to J13t C4 Lk 17- 17 Z7, 4 72, 2H - 'L4 -Sol � I Ir. S V4 sa CTZ . Sck - FT. LA :L 6- 3 -� 3 JH 177 -z -7 1 -4 . 3 V3 Tot T:, J43 => y = 3 C A 6 Ll irlrT-Jaor, 0.v-t=.c3l-b �`t• <s asp.. �. ^:._� D R P�iN /l Gi=- R �e �-- t o��6 /�q C3 LEA-�•Kw � C� 23�x1�+�� •' � EXT�hS lo(y CIF /,/�IfSOrI STR��T �►l TE�CGPTcb T-k- F(^ow GIB LG Vc\oc� y j s lob i V c ! Cl q h rif li. C,�cck LA. R� O��S c \at✓ol C lG �7 mil$ Sh ilk- 2j 35.3 i w"Thlk---�.�. 317 wv -52-?� �z.s� ax.7 - „+"x9.�Z ul }{ `t L AJt Q 21 S•� Arc. 3.o s« �'eUow�hq 2 Ze 6. 6 3.3 tq !1.'S' S•7 tT -- I In .i T ',n• 3 to � 6 In o � 1119017A — lU — '- z LD 1771(10 1J 4 U t Mill Cl C > 1-- L 0 0 1N11101111103 UJ J J �- TI Y IALJ _ I I it N M - r� ' ) R Q In J I J lJ -1 afr i J In N JI z I Z 0 L m m a d X o II IV M LLJ S It , JI H o_ _ _ O z I � O tr 2 iJ J I Y N 0 Q y. o O `1 O it]_—_ c`l Cl -- — p o Z N a N r U - j Cl U W i N 4J 3In � La t u Q u lal ' N N o C4 r tjJl O I c NLLJ N r 11 11 > a t IN;_ - a O O u n \0 F1.CURE 12 I �I. I 1F� 33. I j,, J LLl Q W \� L 11 W Q z 0 a is 0 W 1 L z t J W N Z WWW1 O Q C, U W C1 O J O `P CL a l� p L 0 0 u u N � O N Yl a � 41 N 41 W a•) U a ¢ a a l L u U N N n p u U N 41 W 1" p U 0 b N o a _ N Ci O I f.GUltli ] 2 38 CT I 6 `� Yr A 75ICD fnom4mC r arh - d _ �• J yIl r i= 3•S y AS- - 2.3 CS.g. Gs=b VNAvo c,Z , z6- 5 • �a I' 3 s' C--Cs Qr i �rQG� co uA . AV =31-2-1 �{ i y14s (• C•l� � � = •4 1 er` S�� i