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Home My WebLink AboutGrading Plans - 01/24/2019t:_di�d t' . .. �ta� „�lir3a e ...�. �'ez�i! F_ �,;: ��ere�g � �i�,f�i � m � � ��.�� To: Dan 1Vlogen, EI, CFM Development Review En�ineer � .. . �. � . . .. . . . . . . . . . �_ . . _ � Pr�„�: �?n-�s�-��.;� �,m�;!: iF,S!t,S��1::��.�,�"f�,!.�::.:, 2243 Hiawatha Court Lot 105, Mission Hills First Filing B1808410 Memo and grading plan accepted 1 /24/2019 DJ M Stormwater Engineering & Development Review Division City of Fort Collins Utilities From: Ron Slosson, P.E. CC: Tom Redder Date: January 23, 2019 Re: Proposed Drainage Plan 2243 Hiawatha Courk Back�round Tom and DeAnne Redder, the owners of the property at 2243 Hiawatlla Court, applied for, and were granted a permit to construct a swimming pool to the rear (west) of the house on this property. The swimming pool and adjacent concrete deck are io b� covei•ed with a greei�liouse. The City of Fort Collins granted a variance for the greenhouse structure which was to be constructed under a separate building permit. In the application and public hearing for a variance for the b eenhouse structure, there u�as no mention of a re�uireinent for a drainage report. The swimming pool and surrounding concrete apron were completed in mid-January 2019. The 30' x 50' concrete pool apron was placed continuous with the existing concrete patio to the rear of the house. The ground surface slopes to the rear of the lot with approximately two feet of elevation difference in the 30 feet froin the existing concrete patio to the edge of the new concrete pool apron. This difference in elevation requii•ed that a��roximateiy two feet of fiIl to be placed around the concrete apron. The fill extended nearly level from the concrete apron for approximately four feet on the north and south ends of the apron and eight feet on the west side, then drops to the e�istinb brade at approsimatel}� a 2.SH:1 V slope. The property is in the Mission Hills subdivision and there is no luiown uiast�i• drainage plan for the area. Historical topographic data shows that house was constructed on the high point of the lot with drainage from the front of the house east to the street (Hiawatha Court), and from the rear of the house «�est to the rear of the property, and then souih. At the rear of the property there is no dedicated drainage pathway to the south and the natural drainage is obstructed by fences, sheds, gardens, etc. Due to the lack of a dedicated and unobstructed drainage path from the rear of the property the O�vners and City agreed to divert the runoff from the ne��ly added imper�rious area to Hia��atha Court at the front of the lot rather than along the historic path to the rear of the lot. Page 1 of 3 Hydrolu�v The rational method (Q=CIA) was used to calculate the runoff from the added impervious area. The City of Fort Collins provided the value for T as 9.96 inches. The area A for the added impervious area is I500 square feet (0.034 acres). A coefficient of 1 was used for C because of the small area and complete imperviousness of the addition. Using these values, the resultant runoff flow is 0.343 cubic feet per second. Desi�n As �reviously� discussed, backfitl l�as been place aroui�d the newly coi�structed �uoi apron. The greenhouse structure will be constructed to the edges of the 30' x 50' concrete apron with the ridgeline n.inning the length of structure with gable ends on the north and south and eaves on the east and «iest sides. For both calculation and constructability reasons a channel of circular eross- section was chosen. Elevations of the concrete apron, backfilled areas, and existing ground surfaces were surveyed, and it was determined that a slope of 0.006 would be required to get from the northeast corner of the backfilled area, around the north, west, and south sides of the backfilled area and daylight onto the existing grade at the southwest corner of the house. From the southw�cst corncr of thc housc to I Iiawatha Court there is cnough falt (approximatcly two feet) for the outflow to sheet across the existing grade. It is expected that a small quantity of fill material will be needed between the southeast corner of the greenhouse and south boundary of the property to ensiire all r�moff is directecl to Hiawatha Co�irt. This fill will be obtained from the area between the existing house and south property line in a manner that will increase the slope and create a swale towards Hiawatha Court. This grading will re-direct drainage from the existing downspout on the southwest corner of the house to Hiawatha Court rather than tlie rear of the property. Using a slope of 0.006, a Manning's n value of 0.028 (for short grass), and assuming a circular channel of l.� feet, Manning's equation was used to calculate the flow in a circular channel at various depths. Table 1 summarizes flow and velocity in the channel at depths in 0.1' increments up to one-half the diameter of the circular section. Detailed calculations from the itcrative math program TK Sol�•cr�� arc attachcd. Table 1. Depth (fl) Fl�w (cfs) Velociiy (fUs) 0.1 0.03 0.66 0.2 0.14 1.03 Q.3 0.33 l .32 0.4 0.59 1.63 0.5 Q.91 1.85 0.6 1.28 2.05 0.7 1.68 226 0.75 1.89 236 Puge 2 of 3 The chanr►el will begin at the northeast corner of the backfill at a depth of 0.3'. Because the backfill is essentially level around the structure, the channel will get progressively deeper as it progresses. At the point where the channel terminates the backfill it will be approximately 0.8' deep. Upper banks of the channei will be sculpted to match grade where the channel exceeds 0.75' in depth. Attached is a schematic drawing of the drainage with approximate elevations. Survey in� Spot elevations used for the design were shot with an optical level and are shown on the schematic drawing. tJpon completion of the channel a more complete survey will be performed and submitted in grade certification form. F��'�� ST r p`'�.� �O H. S< '"•F'P .v :' Q �1��5'1��c1��'•.�o ':035173u':• O: '� � d � ��.. .� Page 3 of 3 � h��_ �� /3 Status Rule Satisf r=D/2 Satisf�, Q=1 4q?n"A."R^i2.'3;'S" 5 fiatisf�A= 5"r^?'f�'-sinf��''='— - S2tisf R=A`fCA"ri Satisfi ��=2"(acos�i,r-d;fr}} Satisf P=��`r Satisf V=C��A S2ti5f I hf= 4.63i �Il^L'L`Q"2�12=r. Satisf�he=1=5'V^2`64.� _ Satisf� PJf=(Q�A)+(fg'd',".5} � 'Jariablec Status Input Name � c 15 IC : r L � 02$ n L A. L R 006 S LF � L 2 d L P L V L hf 150 L l he L ' PJf _ . __'^ L -_ � � INT TFeBLE: Results Element � DEPTH � CFS � 1 --- Q3 2 2 14 3 3 33 � d 59 5 5 J1 6 .6 1.2"0 7 .7 1.68 8 75 1.89 _�I � l x .i �4 )�i q _G� 33 Unit 75 1�� 1 �l 125 1 _�195 1.121 1 0299y0�3 ?d3 0013U?�81 0247ngg�g 4058?312E — A.REA. 05 14 25 38 52 .6� a� as _ �❑i� Comment � Diameter of channel _ Channel radius Flor+r in cfs P,Aannings n f0 28 for shcrt grass; A.rea at gr•�en cfepth Hydraulic radius Slopa cf channel Radfan angle Depth in pipe Lti'etted aerimeter Velocit; Pip� Fri�tion Iosses Length of channel Entrance and exit losses Froude �lumber Hydraulic f�adius 06 12 10 23 2^0 .32 36 38 Wetted Pen, VeI4 ?8 66 1 12 1 03 1 39 1.32 1.r3 1 5� 1.u5 1.'6 2.05 1.93 2.2� 2_Od 2.36 2.14 A.NGLE 1 0� 15 1."a� 2 1' 2 �6 Z.?d 3.01 3.14 � ( � I Frictian Losse Ent. and exi Froude # 0 41 �? 0 02 �1 01 04 �2 02 06 43 05 u7 � .1 .09 �1�M1 18 1 44 23 .11 _44 Redder-2243 Hiawatha Ct.jpeg �,�� , � � �� https://mai I.google.com/maiUu/0/#label/! ! 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