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Home My WebLink About1310 LAPORTE AVE., MCKINLEY COTTAGES SUBDIVISION - PDP - 35-04A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTffl%!WMOLI� INV N•b76 VI INv C •b20.69 A PROP 12' DRIVEWAY FOR LOFS 2 AND ] PROP FLOW ARROW (TYPI PROP C'ONTOURS(TYPI I � \ Z LAPORTE AVENUE MUML _/ W. (N).wL% o � (t SO ""Nos RW.y}.69 MV (X)•SQjr.J$ �I M. bxr.n it I TRANSITION LXLSTING SIDEWALK MAX SLOPE = 1 A. EXIST CU'RB.OLTrER AND SIDEWALK TO BE REMOVED CAUTION! EXISTING OVERHEAD POWER LINES i I ! ' LOT 1 ti I I lilt I! I 1 I I oil I j Y LOT 4 I k LOT 2I LOT 3 1310 LUIMIF ARE i 4( , ,1 I EXWT NOY$C I + .L,,_.___. ! 1 I I I I I I ,4". I _ Y me RM.b1010 INV 501S,�r My E I I EXLST GRAVEL' ALLEY JI VAIN (i' PROP IT ALLEY SEE DETAIL ALLEY OPTION B TRANSITION FROM EXIST C60 I'0 PROP ROLLOVER CAKi PROP 12' DRIVEWAY FOR LOTS ]AND 4 EXIST GARAUE AND CONIC PADS TO BE REMOVED I I EXIST HOUSE TO REMAIN REMOVE Lmsrm DRI\'SWAY WITHIN ROW ( PROP ATTACHED SIDEWALK CONNECT TO EXISTING SB)EWALK MANHOLE RM•bN.B$ MN {N).bt5.0$ MY (1O•bJ3.It 20 0 20 40 w x0 FEET SCALE: I--2u Pen NORTH Old Town Subbasin Parameters m Subbas." ID To Conveyance Element ,.: Width (ft)-: Area (acres) Percent Impervious Overland Slope ; (ft/ft) : ` Overland Flow Length (ft 401 422 2150 14.7 80 0.006 300 402 421 2050 9.3 90 0.010 200 405 405 1100 5.1 90 0.006 200 501 501 1150 9.3 25 0.010 350 502 502 2600 12.0 40 0.020 200 503 503 5050 28.9 50 0.020 250 504 504 4500 36.1 50 0.008 350 505 575 3000 27.4 50 0.006 400 506 576 3100 24.8 50 0.007 350 507 507 4150 35.6 50 0.008 375 508 508 2650 15.1 50 0.020 250 509 463 3750 26.0 50 0.010 300 510 475 4750 38.0 60 0.020 350 511 472 3050 21.1 50 0.020 300 512 512 2400 16.6 50 0.020 300 513 464 1650 13.3 50 0.010 350 514 434 1300 7.5 50 0.006 250 515 485 3700 25.3 50 0.008 300 516 516 5650 38.8 50 0.009 300 517 477 2000 16.1 50 0.015 350 518 518 1900 15.4 50 0.015 355 519 519 2300 14.5 30 0.065 275 520 570 1 2400 12.9 20 0.010 235 521 573 2450 22.0 20 0.010 390 522 522 1550 12.4 50 0.006 350 523 523 6650 45.7 50 0.010 300 524 524 5750 26.4 50 0.010 200 525 454 2200 12.5 50 0.020 250 526 490 2900 16.6 50 0.010 250 527 413 3700 25.4 55 0.010 300 528 419 5100 29.3 55 0.008 250 529 604 3450 37.6 75 0.010 475 531 479 2300 18.5 50 0.010 350 532 424 1750 10.0 50 0.013 250 533 425 1850 10.5 50 0.010 250 534 426 4200 29.0 55 0.013 300 535 430 4800 34.5 90 0.005 315 536 811 2350 8.1 1 90 1 0.005 150 T:\OPEMCofcl4\cofcl4 Old town prmtrs tbl-rev.wpd B.1 - 1 Of 14 ANd ERSON CONSUITING ENqiNEERS, INC. The existing gravel alley will be improved to a concrete section, sloped without a crown to drain to a curb and gutter along the southern edge of the alley. The curb and gutter will connect with the side -lot swale to be constructed along the east edge of Lots 1 and 4. Proposed Erosion Control Plan. As an infill project, no street construction or overlot grading is proposed. The developer will provide utility service connections, and sidewalk, alley, and lot drainage improvements. Construction erosion control will be provided by the following two measures: 1) A silt fence will be installed around the perimeter of the project to limit the transport of sediment off -site, and 2) Two construction vehicle access points will be allowed: one off the existing gravel alley at the rear of the property, and a second at the location of the proposed driveway off McKinley Avenue. Vehicle tracking control will be installed at these locations to limit the transport by tire of soil onto the City street system. Construction erosion control details will be presented with the Final Drainage Report and Final Plat utility plans. Long-term erosion control will be provided via lot landscaping. Water Quality. Water quality will be provided using Best Management Practices (BMPs) to filter storm runoff prior to discharging to the street system. These BMPs, to be presented with the Final Drainage Report, will likely include grass swales and/or porous landscape detention. Variances. No variances are requested with this Preliminary Drainage Letter Report. Should you have any questions or require additional information please do not hesitate to contact us. Best regards, QED Associates )P-T3t U__Fv� Kent Bruxvoort, P.E. P.-Wrojects114-101 Jensen I"CstmentlDraimgelLetter Hamdan_05.03.05.doc C C17 . Aaaoeiatea 28[;walnut street.iullrq-$coLLins,co88524-oifice;978.<36.8fi80 ?:fax 976.df8.Ofif11 On -site runoff is conveyed toward the property's southeast corner, at Laporte Avenue, as broad, shallow, cross -lot flow. Proposed Drainage Plan. The Master Drainage Study for the Old Town Basin was prepared assuming a percentage of impervious area for each subbasin defined in the hydrologic model for the Basin. The site is located within Subbasin 504, with a modeled imperviousness of 50 percent (see the attached table photocopied from the Master Drainage Study). The lot, with house and garage, currently has an imperviousness of approximately 10 percent. Subdivision of the lot as proposed into four lots, with sidewalks, houses, garages, and driveways will increase the percentage of imperviousness on the property. The following table provides an estimate of the impervious areas to be created on the property with build -out of the proposed lots. Table 1. Summary of Ex ected Impervious Areas Description Estimated Area (s uare feet) Estimated Percent Impervious House footprints 4,900 20.2 Sidewalks, porches, patios 1,300 5.4 Garages 2,100 8.7 Driveways 2,300 9.5 Totals 10,600 43.8 In the calculations summarized above, 18" eaves were accounted for in the house and garage footprints; and calculations for walks included those from the front sidewalk to the front porch, as well as between proposed detached garages and the homes. The percentage of impervious area on the lots, under the proposed subdivision and corresponding improvements, will remain under the 50 percent imperviousness modeled for the Old Town Basin. Therefore, the contribution of additional runoff from the proposed houses and related lot improvements is already considered in the modeled runoff from the Old Town Basin. No additional storm water detention on the property will be required, and none is proposed. Drainage from the property will be enhanced using soil excavated from the basements of the three proposed home sites to raise elevations in key areas to result in two percent or greater slopes on the property. Drainage will continue to be directed primarily southward on the proposed lots with discharge to the Laporte Avenue gutter. Side -lot swales will be used to direct runoff between homes toward Laporte Avenue. The northern most of the four proposed lots (Lot 1) will be oriented primarily east -west. The rear of this lot will drain eastward to a side -lot swale that will extend along the entire eastern perimeter of the eastem-most lot (Lot 4). The front of Lot 1 will drain to McKinley Avenue, from which the flow will be directed via the east gutter to Laporte Avenue. PAProjectsll4-101 Jensen InvestmentlDrainagelLetter Hamdan_05.03.05.doc' Aasotiates . ,20Ewalnut street, suite - ft coLLins;_co 80524• office.970.d16;0690- fax 970.416.0601, May 3, 2005 Basil Hamdan City of Fort Collins, Stormwater Utility 700 Wood Street P.O. Box 580 Fort Collins, CO 80522-0580 RE: Preliminary Drainage Letter Report McKinley Cottages Subdivision Dear Basil, The following preliminary drainage letter report addresses existing and proposed drainage conditions for the above -referenced project. The project is located in the City of Fort Collins, Colorado at the northeast corner of Laporte Avenue and McKinley Street. The project is a proposed subdivision of a single large lot (about 24,200 square feet) into four smaller lots of just more than 6,000 square feet each. Existing Conditions. The property, 0.56 acres in area, and zoned N-C-L (Neighborhood Conservation, Low Density District) is located within the Old Town Basin. The property slopes from its northwest corner toward its southeast comer at an approximate average gradient of 2.4 percent. Runoff from the property enters the north gutter of Laporte Avenue and flows east toward the intersection of Laporte Avenue and Shields Street where an inlet is located. Flow ultimately discharges to the Poudre River at the Howes Street outfall. Site soils are Fort Collins loam, as presented in the Soil Survey of Larimer County Area, Colorado, by the Soils Conservation Service. This soil is of the hydrologic group B. Minimal, if any, off -site runoff reaches the property. The basin divide is located approximately 150 feet north of the project, at a high point in McKinley Street. Flow from this northem-most portion of the basin is directed down the gutters in McKinley to Laporte Avenue. The project is not located within either a City of Fort Collins or a FEMA floodplain. Mountain Avenue, one block to the south, conveys flood waters eastward through Old Town via Oak Street. Laporte Avenue, beginning at a point about a mile east of the project, also conveys flood waters through Old Town via Howes Street. PAProjectsll4-101 Jensen Invest7nentOrainagelLetter—Hamdan-05.03.05.doc a� Aaaociatea - 2tree[- suite g.- ft cd ins co 80524 • eifi6ef970 <Ib.0600 -lax 970 Z16 0601