2009 - Illinois DNR - State of Illinois

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HYDRAULICSHEC-RAS MODELThe Hydraulic Engineering Center’s River Analysis System (HEC-RAS Version 3.1.3),created by the US Army Corps of Engineers, was used to develop base condition floodprofiles on Farmers and Prairie Creeks. The base conditions model has 7 profilesincluding the 1-year, 2-year, 5-year, 10-year, 25-year, 50-year, and 100-year frequencyevents. The results of the hydraulic model are provided in Appendix 3. Appendix 3 alsoincludes baseline water surface profiles, complex hydraulic structures discussion, andRand Park Pump Station operation plan.Farmers Creek is divided into 2 model reaches, Lower and Upper (see Exhibit 4). TheLower reach starts at the mouth to the Des Plaines River and stretches upstream to theconfluence with Prairie Creek at Prairie Avenue, just east of the Greek Orthodox Churchon Dempster Avenue. The Lower Reach of Farmers Creek is approximately 5180 feetlong and contains 56 cross-sections and 10 stream crossing structures including theclosure gates at the Rand Park pump station. The Upper reach starts at the confluencewith Prairie Creek and heads upstream to just south of Golf Road. The Upper Reach ofFarmers Creek is approximately 4580 feet long with 58 cross-sections and 8 streamcrossing structures.Starting water surface elevations for Farmers Creek at the mouth to the Des PlainesRiver were set to the Des Plaines River 5-year frequency profile elevation as required bythe Des Plaines River Phase II Corps of Engineers study guidelines. However,incorporation of the Rand Park Flood Control Project gate and pump station operationplan into the HEC-RAS model just downstream of Busse Highway, governs most watersurface profile elevations in the lower reaches of the model. The flood control gates onFarmers Creek close when Des Plaines River Stages exceed elevation 624.0(approximately a 1-year frequency flood elevation on the Des Plaines River). Gatesremain closed and pump operations control water surface elevations on Farmers Creek aslong as Des Plaines River flood elevations remain higher than flood elevations onFarmers Creek. The Rand Park Pump Station Operation Plan is included in Appendix 3of this report. Based on this operation plan, gates are closed (and pumps on) for the 1, 2,5, 10, and 25-year frequency events in the baseline HEC-RAS model. A separate HEC-RAS model is used to evaluate 50, and 100-year frequency events on Farmers Creekwhen baseline conditions warrant open gate (no Des Plaines River flood control)conditions. Hydraulic conditions for each alternative flood damage reduction measureconsidered as part of this study were evaluated to determine which gate operationcondition applied to each potential flood control measure for each frequency event.15
Prairie Creek is modeled as a single reach which starts at the confluence with FarmersCreek and stretches to Greenwood Avenue. Prairie Creek contains 138 cross-sectionsover approximately 7800 feet and contains 20 stream crossing structures.Hydraulic modeling of the Farmers and Prairie Creek watershed includes severalcomplex hydraulic structures. These include: culvert and bridge sedimentation,hydraulically long culverts, atypically-shaped stream crossing structures, inlinereservoirs, and 90-degree channel bends. The discussion in Appendix 3 explains thecomplex characteristics of the urban drainage system represented in the Farmers andPrairie Creek model. Flood flow debris has historically collected at various structures onFarmers and Prairie Creek causing additional restrictions and temporarily increased floodprofile elevations. Due to the varied and inconsistent nature of the debris problem fromevent to event in the watershed, the HEC-RAS model does not account for temporaryaccumulation of debris at structures.MANNING’S N-VALUESTable 4 lists typical n-values used in the HEC-RAS model. These values were based onfield inspections and commonly used values. Some reaches required minor n-valuechanges to calibrate the flows based on area precipitation and staff gage data.TABLE 4: TYPICAL MANNING’S N-VALUESLeft Bank Channel Right BankNormal Section 0.06 0.04 0.06High Roughness 1.0 0.06 1.0Low Roughness 0.04 0.02 0.04INEFFECTIVE FLOW AREAS AND BLOCKED OBSTRUCTIONSAs part of developing the HEC-RAS model, buildings that obstructed flow were enteredas permanent ineffective flow areas. This approach allowed the HEC-RAS model toproperly model storage between the cross-sections while ensuring that these areas do notconvey flow.Ineffective flow limits were also used to maintain conveyance channels upstream anddownstream of culverts and bridges. Such limits prevent the model from overestimatingthe expansion and contraction losses associated with restrictive structures in the channel.16
Page 4: Alternative C5 - Pipe From Lutheran
Page 7 and 8: 27. Alternative D6 - Combine Altern
Page 9 and 10: As shown in Exhibit 1, the study ar
Page 11: construct addition flood water stor
Page 14 and 15: PURPOSE AND AUTHORITYThis report hi
Page 16 and 17: infrastructure and commercial devel
Page 18 and 19: Central Road20120220620420710110410
Page 21: TABLE 3: CRITICAL DURATION DETERMIN
Page 25 and 26: TABLE 5 CONTINUED: CALIBRATION DATA
Page 27 and 28: average annual damages under existi
Page 29 and 30: EXHIBIT 5: SAMPLE FLOOD DAMAGE COMP
Page 31 and 32: DAMAGE RESULTS TABLE 8PLAN DESCRIPT
Page 33 and 34: FLOOD DAMAGE REDUCTION ALTERNATIVES
Page 36 and 37: STORAGE IMPROVEMENTSALTERNATIVE S1
Page 38 and 39: Table 9: Alternative S1 - Dude Ranc
Page 40 and 41: Exhibit 7: Alternative S2 - Good Av
Page 42 and 43: ALTERNATIVE S3 - LUTHERAN GENERAL H
Page 44 and 45: Table 11: Alternative S3 - Lutheran
Page 46 and 47: Exhibit 9: Alternative S4 - Luthera
Page 48 and 49: ALTERNATIVE S5 - HIGH SCHOOL RESERV
Page 50 and 51: Table 13: Alternative S5 - High Sch
Page 52 and 53: Exhibit 11: Alternative S6 - Bellea
Page 54 and 55: ALTERNATIVE S7 - LAKE MARY ANNE PUM
Page 56 and 57: Table 15: Alternative S7 - Lake Mar
Page 58 and 59: Exhibit 13: Alternative S8 - Bellea
Page 60 and 61: ALTERNATIVE S9 -COMBINED STORAGE AT
Page 62 and 63: normal flows to bypass the lake in
Page 64 and 65: Table 17: Alternative S9 - Combined
Page 66 and 67: An additional 50 acre-feet flood st
Page 68 and 69: Table 18: Alternative S10 - Combine
Page 70 and 71: the flood storage at the site by ap
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Table 19: Alternative S11 - Combine
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Exhibit 17: Alternative S12 - Dude
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CONVEYANCE IMPROVEMENTSALTERNATIVE
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ALTERNATIVE C3 - DEMPSTER STORM SEW
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ALTERNATIVE C5 - PIPE FROM LUTHERAN
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ALTERNATIVE C7 - REPLACE RANCHO LAN
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OTHER IMPROVEMENTSALTERNATIVE L1- P
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COMBINATION IMPROVEMENTSALTERNATIVE
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damages for 59 structures currently
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Table 22 Continued: Alternative D1F
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Hospital property, north of Dempste
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Table 23: Alternative D2 - Combine
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sewer system would be restricted to
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sewer system would be restricted to
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Page 104 and 105:
Exhibit 31: Alternative D5 - Combin
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ALTERNATIVE D6 - COMBINE STORAGE AL
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Page 112 and 113:
Page 114 and 115:
Exhibit 34: Alternative D8 - Combin
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ALTERNATIVE D9 - COMBINE STORAGE AL
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Existing flood damages along Lower
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Table 30 Continued: Alternative D9F
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ALTERNATIVE D11 - COMBINE STORAGE A
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Exhibit 37: Alternative D11 - Combi
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Table 32 Continued: Alternative D11
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ALTERNATIVE D13: PRAIRIE CREEK CULV
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community can realize additional re
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concrete block or brick veneer over
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CONCLUSIONSFarmers and Prairie Cree
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costs to construct these improvemen
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S1S2S3S7S8S12S11S9D7TABLE 33 Farmer
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2009 - Illinois DNR - State of Illinois

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