Loading...
HomeMy WebLinkAboutDrainage Reports - 08/19/2016MEMORANDUM M J•R ENGINEERING A Westrian Company To: Shane Boyle City"Of Ft,CoQins pro ed Plans. ,App gy From: Tim Halopoff, PE 'OrS1t Dat8 ' I: Date: June 8, 2016 Subject: Kechter Farm -Conceptual Drainage Revision Analysis (Filing 2, Phase 5, Lots 1-6) JR Engineering, LLC has completed a conceptual drainage analysis for lots 1-6 in the 5`' phase of filing 2, of the Kechter Farm project. The following is a summary of the findings discovered while performing a conceptual drainage analysis of the proposed Kechter Farm project in order to determine if the lots in the northwest corner of the site can be graded as garden lots and have rear yard storm runoff drain onto the City of Fort Collins property to the northwest of Kechter Farm; similar to the northeast corner of the Mail Creek drainage basin D3. If lots 1-6 were graded to garden lots (see attached conceptual drainage exhibit), the runoff from the back half of the lots would drain west to the on -site open space tract and be collected in a Swale, from there flows would be routed north to the northwest property corner and onto the City of Fort Collins property to the northwest of the site, see the attached exhibits. This drainage pattern would be similar to that of the Mail Creek Crossing drainage. According to the Mail Creek Crossing Drainage report completed by Northern Engineering in December 2013, runoff from Basin D3 drains to the back of the lots into swales and onto the City of Fort Collins property at the northeast property corner (see Mail Creek drainage exhibit drainage node D3). Historically, the entire Mail Creek site drained to the northeast corner of their site and with the majority of the proposed condition flows draining elsewhere, the proposed minor and major storm event flows entering onto the City of Fort Collins property are considerably less than the historic flow rate. The Mail Creek Crossing report states that the historic flow rates at the property corner were 9.7 cfs in the 2-year event and 44.4 cfs in the 100- year event. The Mail Creek developed basin D3 generates 1.8 cfs in the 2-year event and 7.8 cfs in the 100-year event at the same property corner. See attached excerpts from the Mail Creek Drainage Report. This proposed basin from Kechter Farm creates 0.6 cfs in the 2-year event and 2.6 cfs in the 100-year event. Directly adding these storm flows to the 100 year runoff created from the Mail Creek Crossing site, we get 10.4 cfs in the 100-year event. This new combined basin of D3 and lots 1-6 generate 100-year flow rates within 1 cfs of the historic 2-year event at this location. The grading of the 6 Kechter Farm lots into garden style lots would create a minor increase in runoff onto the City of Fort Collins property, the total developed basin draining to the City's property is significantly less runoff than the historic condition. In fact, the developed condition drainage basin essentially would meet the City's requirement of 100-year developed flow rate down to the historic 2-year event, without detention necessary. Additionally, the water quality for this minor change is handled in the proposed natural Swale and the grass buffer on the City of Fort Collin's property. Thus, we request approval to revise Kechter Farm, Filing 2, Phase 5, Lots 1-6 from A to garden style grading. Sincerely, Tim Halopoff, PE 07200 South Alton Way, Suite C400 0130 East Kiowa Street, Suite 400 F!12900 South College Avenue, Suite 3D Centennial, C0801 l2 Colorado Springs, C080903 Fort Collins, C080525 303-740-9393 9 Fax 303-921-7320 719-593-2593 • Fax 303-921-7320 970491-9888 9 Fax 303-921-7320 N m qx d x X x N N C t m 6 Vl YI ma— x . d a? X t m n m ni m E A t7 Y m C .2 m A V O O 9 ¢ X X" E X X u X x L °p m m u E 3— O V � N � N N ¢ X 6 E yx e X ¢ V m m a d O H O � � ¢ O m ~ o _ 0 q C O O m V u C N O O m d V 3 q O y c d 0 V O C A 3 m a' d N V � c m d o � 3 �" oN N V q a u � o x a N C q J o C Y (V � V C. O d d V i N M m m c O 3 ; m o u O R' q N u o Q O L m O V ym G Q V {C 1D q q O O f c a O q m ~ N Q C L N o c o 0 o c o o 0 0 b h .'1.'e: b O 04 AI G h i G G N 0 J Q C e'I z LL y E d C E m O N d j 112 Q O V m r O = W Q S m U N H H m � � � N n f E o u C E N O J � > x W O n ~ — W � Y• F ae O � � N O y � m � _ � E M z 5 � C Q f Z N � S � b u p V v 0 O N x N Z n m � F E m N O O o l7 V = N Q V � 2 � Q m U Y N N O N N u c a Yl a d c m 01 0 d y > d H O N d o z F L d N Ip W 6 V V u b b Ic G C C O O O O O O a � d s 01 N m m o E x I v ^ E m m d m J O m N E of o w Ic o 0 c N c Ill b o a o d o m •� Y % ^, n m o f Lc c � m c d u N •Y a c o. a c 0 W m O d N N ry 0 o c c u a y.'o_ a E c ^ 0 V d m m C d N '2 C m L •= o'' - T m « w E d ° m Ko d> j N an d a m c u y lY Q o II 3> J E o m d 11 II � II d II W L N i ~ I I I J 11 O J C z a. v LL LL LL z W W Q W H H W z Z G cr C O R; a Q (ulw) ' W i P J W (sdj) Alpola (u)47gua f (sa4Jui) azis adi (s�J) mod j u8rsa W (sp) molj laws G' (%) OdOJS LL Is1J) z POO ae J (Jv) v. 0 (ulw) J (sly) O POO m LL LL IJv) v* N m O O z w (ulw) ' .ai G w m wFS •yao:) jjoun o (Jv) eai pI uise a lwod uRlsa W R' N M LL C� G O W 0 z c z Q F E Y C S (ulw) W j W (sd1) A1pola 41sua (sapuj) azis adi W (s)7) MO�j u�lsa (s)7) MOIA UWA cc to (%) adolS (sp) z G4/ul) w J 0 (ww) 31 (sp) ID U4/ul) m 0 a 0 z 7 G c •Ijao:) j4oun a (ay) eaj p� uise ¢ luiod ueisa .. H W OC h 1N)r—'HOW lNU �. �. —:`—•— i 1 •III I i I ' 1 I 1 r �, � I" I� 1r 1+ � 1 [ I 1 1. .. I� � L � ,r I 1 -+ 1 !., I 1I ,,-�r 1� I_. _- I�� �' � � Ir'I _ � ; .e • 1 •� Lrr�l a 1 I I 1 r 1�1 1 I � II Ir V1 I 1 I.r l I I 14�1 .. I 1 Ir� I � 1 Irr. . II11+ I I'rr • .r In I I "•.. IF r �-u, I �I u .• w. 1 I � 1 I 1 1• — '{ � 1�-'1 .I 1 1 1 hrN 1 1. 'ir 11. 1 I —_�. I 1 r Iy .vV I � I 1'r t. r• I 1 1 Irn, l �, 1111+ - 1 .I�rIN W 1 �_��—ram.. 11 I r I I�'.1. rr• J� I�I It1��, •r ''�'y I u I • _ I �� � U. N ` ILI •.1 Iv . � P \ �j 1. 1 � I , _ , u - n•� �.—_-I �1��/r I I• 'er 11 �����f J11 •.� i www 1` n wxw 1 1 n l nrr I i r w .. I —� I41iN 1 1' •i Z� 1� 1 1 _-4)1 •i� �� 1 1 III SPRUCE CREEK DRI — — VE — —� FNGINFFR'S STATEMINI //II e -n-7s ' 1'iIY of 1'erl l•.IIWIe, l illlxw4� tT'll.l` AI'PHn�':V S Knaw *fiat below. '1'LA� 1°i3%I .. " Call belme you dig�/— rwiVsv4'.C41 -- Jyv� w-\ 1 .I r Vrrn. llir.r IWr �}1 urn I annlo l'Inrnli, l"dlnw111 1 1 AIJA llj^ .AITNI I% r -2�>Nr ,.dF Lam..+• nI, IMP z z a� fq-1 2361 -' INORTHERN ENGINEERING MAIL G includes developed runoff from future undeveloped area, one single-family lot and approximately 0.06 acre of Piney Creek Drive. The proposed developed flows (i.e., Q2=0.77 cfs and Q,00=3.35 cfs) from this area are comparable to the existing flow estimates (i.e., Q2=0.0.64 cfs and Q,00=2.95cfs). In general, we anticipate the impact from our developed runoff to be negligible. 8. Sub -basin D3 wraps around the northeast corner of the project site. It is comprised of the back half of fifteen single-family lots. The current proposal shows the developed runoff from D3 draining into a swale along the east property line and sheet flowing across the north property line. The existing runoff draining to these property lines generally flows overland and into shallow swales. At the confluence of these swales, which is the northeast property corner, the existing runoff flows north in an existing concentrated flow path. The character of the proposed drainage patterns is generally consistent with the existing condition. Additionally, the minor and major storm event flows that we propose to drain at D.P. D3 are considerably less than existing flow rates. The entirety of the existing property (38.7 acres) historically drains to the northeast corner of the site. This historic basin generates 9.7 cfs in the 2-year event, and 44.4 cfs in the 100-year event. Developed sub -basin D3 (1.78 acres) generates1.8, and 7.8 cfs in the 2- and 100-year events. 9. Sub -basin D4, which includes the front half of two single-family lots and 0.1lacre of Tilden Street will drain to a portion of Tilden Street that was designed with Kechter Crossing. The additional flows should have no adverse impact during the 2- and 10-year storm events. During the 100-year storm event, the additional flows may cause ±1cfs to bypass the proposed on -grade inlets at the intersection of Tilden Street and Kechter Road. 10. We are working with the New Mercer Ditch Company on the Mail Creek Irrigation Ditch crossings designs. Mail Creek Crossing will cross the Mail Creek Irrigation Ditch at three locations: • Tilden Street • A pedestrian crossing to the east of Piney Creek Drive 1 1 p/ is unofficial copy was downloaded on Apr-I8-2016 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com 7 l lf/W UAMIE/PAMFIAS I I AM!)eG fe. OWNER NFI:NiFR f.Nr1SCIMfl OWNER E OEN STREE rr (6T RavJ ®a®mm®mmm� �QQQQQQQ�QQQQQQQQQQQQ�QQ�QQQQQ�QQQQQQQ�QQQQQQ�QQQQQQQ�QQ�' aQQQQQa�amm®m®m as®mQQ.�ammmm m•��m��QQ��mm®m 00mmmmmmm QSQQQ��®��mmmm® QOm��s�QQ[x�■ mmm 0a m �0E■EC)• QQQQ©Qs�� ��mmm asQQQQQ®m®mm®m aam•Q�mmmE�m QQQQQQQQQQQQQ.QQQQQQQQQQ�QQQQ��Q�QQQ[Q�QQQQQQ�Q�QQQQQQ�QQQQQQQQ. QOE000QQ�QQQQQ��i7® ®m�� �!•�3•E000QEk1!♦SI' c`��'IJ�Ey]♦QQQ[S')•�dl�l3ls s:J•SYJ•�M!•�1U' ' ��'d:�s[61•!Ed'!•�[[�ibk'J• �����a ��'sLJ•�lk>•�d:�1 l`-r9 �11JJ NORTH Tao 0 — $ 0 200 3wr°.1 (IN FEET) MM. iMN LEGEND: PPO n SIM. $EWER PROMSED UNDEa0loiN �• PIWESED IWEI B PROPOSED COMOLW vJ E]( HG CCNIOUR MOPDSED Av — — — MMOBEO CURB • GUTRR MOPERTr BGMGARY OESIW i'my Q ELM MAINAW DAM LABR �We A nNpE camm� WMNADE SAM 8011NDANT ■ ■ mm= SWAIL MUN 1� NOTES: - 1. WM TO MF rMM WMNAGE ANB ERO9W rAN RE➢MT FM E MNL MEFN WOSWC BY NMTIIFRN EN4INEERMG, DATED DECEMBM IB, $ i 201 3 FW ADnnaNM INEDNVAnM, 'o (D H FOR DRAINAGE REVIEW ONLY NOT FOR CONSTRUCTION City of Fort Collins, Colorado UTILITY PLAN APPROVAL 'Im L. M1 EOPy D.L° ':NECKED BY. WA R.L.. R wLn.w uwHy -D�1� NEreFD Rr _HEUED BY —tss A A•°"°°°" D°L• Sheet ]NEEAED 8... D R 1 HRZNED Rr E"""'"""'"���•�� na1 Of 54 Sheets