|
<br />coefficients for conveyance elements were increased by 25 percent. Two types of conveyance
<br />elements within catchment areas were simulated using channel elements; a grassed channel and a
<br />street The grassed channel simulates the channel in catchments dominated by open space and/or
<br />agricultural activities The street channel simulates stormwater transport in catchments dominated
<br />by de,'elopment, Typical parameters used tor conveyance elements are shown in Table 5
<br />Catchment widths and conveyance element parameters for individual catchments are listed in the
<br />computer output summary in Appendix A
<br />
<br />Table 5, Typical ConvC)'ance Element Pllramelers
<br />
<br /> D(~h Side Slope, Manningn' BottomWidt.'l
<br /> H:V I~Order 2 Order 3 Order ,
<br />Lnannel
<br />Main , 3 3:1 0,044 , 7,5 10
<br />Overt1ow 10 20:1 0,056 23 25.5 28
<br />Slrut ,
<br />Main 0.5 3:1 0-020 , . . .
<br />Overflow , 10 20:1 ON4 , '1 '1 , 11 ,
<br />
<br />'increaso:dby2S%
<br />
<br />C. Calibration
<br />
<br />(
<br />
<br />Hydrographs produced by UDSWM arc calibratcd to CL'HPF hydrographs for the IOO-year event
<br />using the five catchments within the study area sho\vn on Figure 4 in Chapter II Flood peak
<br />~alibration 1S summarized on Table 6 (VJ-lPF and L'DS,",,':\!! ttoo,] hydrograph~ lor the 100-year
<br />evcnt are compared on Figure 8, All individual or contiguous catchments in the study area meding
<br />the following criteria were used tor calibration, (1) area less than 200 acres, (2) reasonably uniform
<br />shape, (3) length-width ratio less than 4, and (4) catchment slope between OJ105 and 0,037 !lift,
<br />Flood peak and hydrographealibration forc'l:isting and fitture percent i mperviousness was achieved
<br />by multiplying the UDSWIv\ catchment width parameter~ for all catchment~ by I 8 This
<br />multiplication factor was also applied 10 the catchment width parameter for all other ,torm events
<br />(0,4-ineha\'eraileslorm.a!\d2.,5-.1O-.and50-vearewnts)
<br />- .
<br />
<br />Tahle 6. Flood Peak Calibration, CDSW:\I to Cl'HPF
<br />
<br />Ex;.\,t,,, Percentft"l'erv,ollsne$,'
<br />Catchment-- r----Fl00dPeak (efs) % different from
<br /> , CUHPF
<br /> , CUHPF UDSWM
<br />221(PT) I '" 18J 3%
<br />212/213(PT) 188 187 -1%
<br />430(CC) ; 1M 163 .1%
<br />440/442 (CC) 186 2'- 20%
<br /> -, I
<br />645IBC) "" 21' 5%
<br />
<br />FUllIrePercenlf iou.,ne$s
<br />Catchment Flood Peak (cfs) %differentfromi
<br /> CUHPF I
<br /> CLBPF lJDSWM ,
<br />221(PT) 396 361 -9%
<br />212/213(PT) 503 435 -14%
<br />430(CC) 204 204 0%
<br />440/442:~)C) 190 2'0 21>%
<br />645 C 204 2lS 5%
<br />
<br />NOlO PT" Prince Tributary, CC" Coal Creek Tributaries,
<br />BC=BollJderCreekTributarie,
<br />
<br />D, Detention Areas
<br />
<br />FOllr derention fadlitie, located ",ithin subdivisions (Arapahoe Ridge r-;o, t, Arapahoe Ridge No ::.
<br />Orchard Glen riling ;.10, I, and Canyon Creek Filing No. I) were incorporated in the existing and futurc
<br />conditions hydrologic models, Design information tor these detention facilities was obtained Irom the final
<br />drainage reports for these subdivisions, There are no as-built plans available for these detention fae.ilities,
<br />Field inspection indicates some of the dctention facilities were likely not eonstructed according to the final
<br />drainage reports Two SlOan detention facilities located in Harvest Point subdivisi<)ll were not modeled
<br />beeauseofan absence of design information,
<br />
<br />Inadvertent swrmwatcl detention at such areas as stock ponds and at railroad embankments was generally
<br />nM modeled An undersized eu]vert below the abandoned BI'."RR embankment near ;.Iortheast County Line
<br />Road was modeled to include delemion upstream of the embankment caused by the culvert, using design
<br />intormationobtainedfromaerialphotographyandfieldinspection.
<br />
<br />Rating curves tor the detention facilities are developed using Federal Highway Administration ~lodel HY.8
<br />computer program (federal Highway Administration, 1996), the orifice equalion (C .. 0,62 (UDFCD,
<br />1969)), arld the weir equation (C = 3,0 (UDFeD, ]9(;>9))_ Stage/slOrage relationships ",ere obtained from
<br />the tinal drainage reports Storage/dbcharge relationships for detention area> are listed in the computer
<br />output summar)' in Appendi~ A
<br />
<br />1J1-2
<br />
|