HYDROLOGY REPORT BOSLEY WASH DETENTION BASIN MESA COUNTY, COLORADO

Transcription

1 Offices: Arizona Colorado Wyoming Montana Arizona Oregon Washington Alaska HYDROLOGY REPORT BOSLEY WASH DETENTION BASIN MESA COUNTY, COLORADO December 2017 Prepared for: Mesa County Public Works Attn: Carrie Gudorf P.O. Box Grand Junction, CO 81502

2 Table of Contents Bosley Wash Detention Basin Hydrology Report 1.0 Executive Summary Introduction Basin Characteristics Basin Delineation Soil Types Precipitation Losses Constant Loss Method Loss Value Determination Hyetograph Development Probable Maximum Precipitation (PMP) & Frequency Precipitation Temporal Distribution General Storm Temporal Distribution Local Storm Unit Hydrograph Development Colorado Plateau Unit Hydrograph Unit Hydrograph Result Reservoir Routing Rainfall Runoff Model Results References Table of Tables Table 1: Bosley Wash Detention Basin Performance Summary... 2 Table 2: USBR Recommended Ultimate Infiltration Rates Table 3: Bosley Wash Ultimate Infiltration Rates Table 4: Composite Ultimate Infiltration Rate Comparison Table Table 5: General Storm Precipitation Depths Table 6: Local Storm Precipitation Depths (Factored by 0.45) Table 7: Local Storm PMP Hyetograph Comparison Table Table 8: Colorado Plateau Synthetic Unit Hydrograph Parameters Table 9: Spillway Crest and Dam Crest Elevations Table 10 : Bosley Wash Detention Basin - Stage-Area-Storage-Discharge Table Table 11: IDF & Reservoir Routing Results Table of Figures Figure 1: Vicinity Map... 4 \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page i

3 Bosley Wash Detention Basin Hydrology Report Figure 2: Drainage Basin Map... 7 Figure 3: Hydrologic Soil Groups... 8 Figure 4: SMU Designations and Saturated Soil Hydraulic Conductivity Map... 9 Figure 5: General Storm PMP Depth Duration Curve Figure 6: General Storm PMP Hyetograph Figure 7: Local Storm PMP Depth Duration Curve Figure 8: Local Storm PMP Hyetograph Figure 9: Bosley Wash Synthetic Unit Hydrograph Figure 10: Bosley Wash Basin Parameters Exhibit List of Appendices Appendix A Hyetographs Appendix B Infiltration Worksheets Appendix C Unit Hydrograph Worksheet Appendix D Spillway Discharge Worksheets Appendix E HEC-HMS Output \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page ii

4 1.0 EXECUTIVE SUMMARY Bosley Wash Detention Basin Hydrology Report This second revision (R2) of the Hydrology Report was revised to incorporate Colorado Dam Safety review comments on the first revision (R1) of the report. In addition, in the process of resolving Dam safety comments, a minor error in the stage-storage relationship was discovered and corrected; this error results in a minor improvement in the anticipated performance (i.e., reduction in the maximum water surface elevation) during the Dam Safety IDF. The principal report revisions include: 1. The discharge capacity of the low-level outlet is not included in the IDF routing. 2. The discharge capacity of the emergency spillway is now included in the IDF routing. 3. The supplemental simulations demonstrating the potential range of antecedent conditions and anticipated dam performance were removed. Simulation results for the most severe antecedent conditions (i.e., initial abstraction = 0 inches) are presented for initial water surface (IWS) elevations of 4,800 ft (no water behind the dam) and 4,806.5 ft (water behind the dam up to the spillway crest). 4. Correction of the stage vs. storage curve. 5. All of the IDF routing summary tables were updated to reflect the revised and corrected model input parameters. This report presents the results of the Inflow Design Flood (IDF) analysis for the proposed Bosley Wash detention basin. The sole purpose of the dam is for flood control to protect the downstream development from flooding through up to the 100-year flood. The Bosley Wash detention basin will be classified as a minor, high hazard dam. The hydrologic analysis for computing of the IDF and design of the spillway system was performed in accordance with the State of Colorado Dam Safety s Rules and Regulations for Dam Safety and Dam Construction. From the Rules and Regulations for Dam Safety and Dam Construction, the IDF for a minor, high hazard dam is shall be derived based on 0.45 PMP, where PMP is obtained from the applicable hydrometeorological report. PMP depths for both the 6-hr Local and 72-hr General Storm were determined using the Hydrometeorological Report (HMR) No. 49. Despite the greater total precipitation depth of the General Storm, the greater intensities that will occur during Local Storm PMP will produce the more severe hydrologic loading on Bosley Wash and is the basis for the design storm in computing the IDF. The area tributary to Bosley Wash is approximately mi 2. The basin extends from a low point near I-70 up to the top of the Bookcliffs. The lower third (approximately) of the \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 1

5 Bosley Wash Detention Basin Hydrology Report basin is characterized as moderate slopes with sparse, brushy vegetation, and the upper two-thirds (approximately) is characterized as steep, bare slopes. Soils in the basin are generally classified as sand and exposed rock with moderate to high runoff potential. As recommended in the Hydrologic Basin Response Parameter Estimate Guidelines for Colorado (the Guidelines), the Colorado Plateau dimensionless unit hydrograph was used as computing the rainfall-runoff hydrographs for the Bosley Wash IDF evaluation. Table 1 presents the peak inflow to, and outflow from, the proposed Bosley Wash detention basin during the IDF. Table 1: Bosley Wash Detention Basin Performance Summary Unit Hydrograph Inflow (cfs) Peak Stage (ft) Discharge (cfs) IDF (0.45% PMP) 4,426 4, ,981 \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 2

6 2.0 INTRODUCTION Bosley Wash Detention Basin Hydrology Report Bosley Wash is located north of I-70 and east of the Clifton interchange around 34 Road, west of Mt. Garfield. Bosley Wash is a mixed desert and agricultural watershed located east and northeast of Grand Junction, Colorado, in Mesa County. Figure 1 shows this location of Bosley Wash in Colorado. The watershed extends from the rim of the Bookcliffs south to the Colorado River, crossing beneath Interstate I-70 (I-70) via an 8-ft x 8-ft reinforced concrete box culvert (RCB). Development in the wash is limited to the portion of the watershed south (downstream) of I-70. In the current condition, stormwater originating from Bosley Wash flows through residential, commercial, and agricultural areas, and has caused flooding and severe property damage. Flooding has been relatively frequent, occurring both upstream and downstream of I-70 (overtopping or nearly overtopping the freeway, resulting in a fatality in 2006). The Bosley Wash detention basin project is being funded through a grant from the State of Colorado Department of Public Safety Division of Homeland Security and Emergency Management (the State) for the sole purpose of flood control. Given the historical impacts from flooding (i.e., fatality on I-70 in 2006), the detention dam design is based on the assumption the dam will be classified as high hazard. Further, the dam geometry has been designed to limit the maximum section height to less than 20-ft, and the dam will be classified as a minor, high hazard dam. The funding agreement between the State and Mesa County (the County) requires the detention basin be constructed to capture and detain stormwater runoff from the upper Bosley Wash basin for runoff events up through the 100-year flood, releasing detained runoff at a maximum release rate of 50 cfs. However, to comply with the Rules and Regulations for Dam Safety and Dam Construction, the Inflow Design Flood (IDF) used to size the dam and embankment structure was derived from the 0.45 PMP, where the PMP was obtained from Hydrometeorological Report 49 (HMR 49). \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 3

7 Bosley Wash Detention Basin Hydrology Report Figure 1: Vicinity Map \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 4

8 3.0 BASIN CHARACTERISTICS Bosley Wash Detention Basin Hydrology Report 3.1 BASIN DELINEATION DOWL delineated a mi 2 drainage area tributary to the proposed Bosley Wash detention basin using digital, 1:24,000 scale, USGS topographic maps, National Elevation Data (NED, 10m Resolution), and LiDAR mapping. There are no tributaries or topographic features that would be better represented by subdividing the basin. Figure 2 presents a map of the Bosley Wash basin. 3.2 SOIL TYPES Soils data for the drainage basin were obtained from the National Resources Conservation Service (NRCS) Soil Survey Geographic Database (SSURGO, The NRCS SSURGO data base was used to identify soil properties, such as hydrologic soil group and infiltration rates. Infiltration rates assigned in the hydrologic model were determined considering both hydrologic soil group (HSG) and the saturated soil hydraulic conductivity (Ksat). The NRCS soil mapping coverage of the Bosley Wash basin identifies three hydrologic soil groups: HSG B, HSG C, and HSG D, but for a large percentage of the basin area (approximately 40%), the NRCS soil mapping does not include assignment of a HSG. Where the HSG is not assigned, DOWL assigned an HSG based on the published saturated soil hydraulic conductivity for those areas. The NRCS define HSG B as: Hydrologic soils group B soils have a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. The NRCS defines HSG C as: Hydrologic soils group C soils have a slow rate of infiltration rate when thoroughly wet. Water movement through these soils is moderate or moderately slow and they generally have a restrictive layer that impedes the downward movement of water. The depth to the restrictive layer is greater than 20 inches and to a permanent water table is deeper than 2 feet. The NRCS defines the HSG D as: Soils in hydrologic group D have a high runoff potential. These soils have a very slow infiltration rate when thoroughly wet. Water movement through the soil is slow or very \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 5

9 Bosley Wash Detention Basin Hydrology Report slow. A restrictive layer of nearly impervious material may be within 20 inches of the soil surface and the depth to a permanent water table is shallower than 2 feet. The NRCS SSURGO hydrologic soil group map is shown in Figure 3 and the soil map unit (SMU) designations and the associated saturated soil hydraulic conductivities are shown on Figure 4. \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 6

10 Bosley Wash Detention Basin Hydrology Report Figure 2: Drainage Basin Map \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 7

11 Bosley Wash Detention Basin Hydrology Report Figure 3: Hydrologic Soil Groups \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 8

12 Bosley Wash Detention Basin Hydrology Report Figure 4: SMU Designations and Saturated Soil Hydraulic Conductivity Map \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 9

13 Bosley Wash Detention Basin Hydrology Report 3.3 PRECIPITATION LOSSES Soil type, vegetation type and density, and the antecedent moisture condition directly affect the rate and quantity of rainfall runoff through the processes of interception, infiltration, surface storage, and evaporation. The sum of these four processes is referred to as cumulative precipitation losses and is often represented by two parameters: initial losses and infiltration losses. Infiltration is the process by which precipitation moves downward through the surface to recharge aquifers and support base flow in streams. Infiltration capacity varies in both space and time within a given watershed. Spatial variation of infiltration capacity occurs due to differing surface conditions, such as soil type and vegetation, and temporal variations occur as the wetting front progresses downward through the soil column until the soil becomes saturated and the ultimate infiltration rate is achieved. DOWL applied the Constant Loss Method to estimate the ultimate infiltration rate Constant Loss Method The constant loss method is a simple, yet reasonable, method for computing precipitation losses during extreme rainfall events. An initial loss (depth) and a constant loss rate (depth/time) are specified for this method. The premise for this method is that after the initial loss is satisfied, rainfall is lost at a constant rate over the remaining duration of the storm. The initial loss represents depression storage, evaporation, and interception and is a function of the antecedent moisture conditions (USACE, 1994). For this analysis, DOWL assumed a range of potential initial abstraction values, from 0.0 inches to 0.5 inches. Table 2 presents the constant infiltration rates identified in the USBR Flood Hydrology Manual using hydrologic soil group as the only soil parameter for selecting the ultimate infiltration rate. Table 2: USBR Recommended Ultimate Infiltration Rates Ultimate Hydrologic Infiltration Soil Group Rate Range (in/hr) A B C D \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 10

14 Bosley Wash Detention Basin Hydrology Report Alternately, the saturated soil hydraulic conductivity (Ksat) for specific soil types can be obtained from the NRCS SSURGO system, which utilizes basin specific data for estimation of the ultimate infiltration capacity. Based on the Hydrologic Basin Response Parameter Estimation Guidelines for the State of Colorado (page 51, Determine Controlling Soil Horizon Layer) (George V. Sabol, 2008), for storm frequencies up to the 100-year event, the effective depth of infiltration is approximately six inches; however, for less frequent storms up to the PMP, at least the top 12-inches, but no more than 18-inches, should be considered. For soils in the Bosley Wash basin, DOWL obtained the limiting Ksat values over the range of 0 to 12-inches below ground surface from the NRCS Web Soil Survey website. Table 3 presents the breakdown of SMUs in the Bosley Wash basin and their associated Ksat values for the 12-inch depth range. The values presented reflect the vertically weighted average of the most limiting hydraulic conductivity values for each SMU. Also presented in the table are the bare ground infiltration rates by soil type from Table 10 of the Guidelines. Soil Map Unit Symbol (SMU) Table 3: Bosley Wash Ultimate Infiltration Rates Area (mi 2 ) Hydrologic Soil Group KSat (in/hr) Sabol, Table 10 (in/hr) Soil Texture of Infiltration Limiting Soil Horizon D Badland entered as clay Very shallow weathered bedrock B* % - Sandy Loam 30% - Clay 30% - Sandy Clay Loam D* % - Silty Clay Loam 55% - Clay B % - Silty Loam 30% - Clay Loam 25% - Sandy Loam C % Loam *Assumed HSG The Ksat values presented in Table 3 are the bare earth values, unadjusted for vegetative cover; vegetative cover generally increases the infiltration rate for a given soil type. Limiting Ksat to the bare earth values incorporates an additional level of conservativism (i.e., uses a lesser infiltration rate). \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 11

15 Bosley Wash Detention Basin Hydrology Report When more than one soil type is present within a basin, the composite infiltration rate should be calculated using weighted areas. The composite ultimate infiltration rate was calculated using Equation 1 (below). This equation is taken from Hydrologic Basin Response Parameter Estimation Guidelines (George V. Sabol, 2008), and is appropriate for use with log-normally distributed parameters, such as infiltration rates for different soil types. The composite ultimate infiltration rate for the Bosley Wash basin is presented in Table 4 (the composite ultimate infiltration rate worksheet is provided in Appendix B). Where, Equation 1: Composite Ksat Composite Ksat = alog 10 ( A ilog 10 Ksat i A T ) [1] [1] Note: alog10 is the antilog function Ksati = bare ground hydraulic conductivity for a SMU, in/hr Ai = component area of SMU, mi 2 AT = size of subbasin = mi 2 Table 4: Composite Ultimate Infiltration Rate Comparison Table Infiltration Reference Composite Ultimate Infiltration Rate (in/hr) NRCS SSURGO Ksat 0.26 USBR HSG B, C, D Range (min max) Sabol, Table Loss Value Determination In evaluating the sensitivity of infiltration rate on the IDF hydrograph, the NRCS SSURGO composite value of 0.26 in/hr produces an effective precipitation of approximately 80%; conversely, the maximum ultimate infiltration rate for a HSG D soil type of 0.05 in/hr results in an effective precipitation of greater than 90%. Based on discussion with the Colorado Department of Natural Resources (DNR) Dam Safety Program staff, the composite ultimate saturated soil hydraulic conductivity for bare ground by soil texture (Table 10 from Sabol) was selected for use for computing excess precipitation in the rainfall-runoff model. \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 12

16 Bosley Wash Detention Basin Hydrology Report 3.4 HYETOGRAPH DEVELOPMENT Probable Maximum Precipitation (PMP) & Frequency Precipitation Colorado rules require computation of the Inflow Design Flood based on the PMP. By definition, the PMP is the theoretically greatest depth of precipitation for a given duration that is physically possible in a particular geographic location at a certain time of year (Hansen, Fenn, Schreiner, Stodt, & Miller, 1988). DOWL used the National Weather Service s HMR 49 to calculate PMP depths specific to the Bosley Wash basin for both the 72-hr General Storm and the 6-hr Local Storm. Depending on the size and hazard classifications, the State of Colorado s Rules and Regulations for Dam Safety and Dam Construction allows for a reduction in PMP. The Bosley Wash dam will be classified as a minor, high-hazard dam, and the rules specify a design storm depth of 0.45 PMP (refer to Table 5.2 on page 19 of State of Colorado DNR, 2007). Table 5 and Table 6 present the General Storm and Local Storm PMP depths as determined using HMR 49. Table 5: General Storm Precipitation Depths Source General Storm PMP (1 mi 2 ) - inches 6- hour 12- hour 18-hour 24-hour 48-hour 72-hour HMR No Factored by 45% Source Table 6: Local Storm Precipitation Depths (Factored by 0.45) ¼- hour Local Storm PMP (1 mi 2 ) - inches ½- hour ¾- hour 1- hour 2- hour 3- hour 4- hour 5- hour 6- hour HMR No Factored by 45% Temporal Distribution General Storm To develop the General Storm PMP hyetograph, it is necessary to compute incremental precipitation depths for the desired model time step (five minutes) between the index precipitation depths (0, 1, 6, 12, 24, 48, and 72 hours). Thus, for this IDF study, the incremental precipitation depths were computed by linear interpolation between the bounding index precipitation depths. The Depth-Duration curve for the General Storm PMP is shown in Figure 5. \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 13

17 Precipitation Depth (inches) Bosley Wash Detention Basin Hydrology Report General Storm PMP Depth-Duration Curve Time (Hours) Figure 5: General Storm PMP Depth Duration Curve Once computed using linear interpolation, the incremental precipitation values were temporally distributed to create a late-peaking storm arrangement as defined in the in the USBR s Flood Hydrology Manual. The late-peaking distribution places the largest increment at the 2/3 point of the storm (i.e. 48-hours), then places the second and third largest increment, respectively, in front of the largest increment, then the fourth largest increment immediately behind the largest increment, continuing this alternating pattern until all increments are used. Figure 6 presents the precipitation hyetograph for the late-peaking General Storm PMP; the incremental precipitation depth values for this distribution are included in Appendix A. \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 14

18 Incremental Precipitation (inches) Bosley Wash Detention Basin Hydrology Report PMP General Storm Hyetograph Time (hours) Figure 6: General Storm PMP Hyetograph Temporal Distribution Local Storm The Local Storm PMP depth-duration curve was temporally distributed in accordance with the EM (U.S. Army Corps of Engineers, 1965) and HMR No. 5 (U.S. Weather Bureau, 1947); the distributions are similar, with EM peaking after the center of the storm and HMR No. 5 peaking before. HMR 49 (National Oceanic and Atmospheric Administration, 1984) states, In application, the choice of [EM or HMR No. 5] is left to the user since one may prove to be more critical in a specific case than the other. Consistent with the guidance in HMR 49, both distributions were evaluated, and the distribution that resulted in the more severe hydrologic loading was selected. As for the General Storm, the incremental precipitation between index precipitation depths was computed using linear interpolation. The depth-duration curve for the Local Storm PMP is shown in Figure 7. \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 15

19 Precipitation Depth (inches) Bosley Wash Detention Basin Hydrology Report 12 Local Storm PMP Depth-Duration Chart Time (Hours) Figure 7: Local Storm PMP Depth Duration Curve For rainfall-runoff model simulations using the Local Storm PMP depth (all other model parameters being equal), EM results in the more severe hydrologic loading (Table 7), and Figure 8 presents the corresponding Local Storm PMP hyetograph. Note that the peak runoff rates presented in Table 7 were developed using assumed parameters for the purpose of determining the temporal rainfall distribution that produces the greatest peak runoff rate. Subsequent to this comparison, the basin parameters were refined and these values do not represent the final analysis. The tabular hyetographs for both Local Storm PMP storm distributions are included in Appendix A. Table 7: Local Storm PMP Hyetograph Comparison Table Peak Hyetograph Runoff Distribution Rate (cfs) EM ,829 HMR 5 2,803 \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 16

20 Incremental Precipitation (inches) Bosley Wash Detention Basin Hydrology Report 1.0 PMP Local Storm Hyetograph (EM ) Time (hours) Figure 8: Local Storm PMP Hyetograph 3.5 UNIT HYDROGRAPH DEVELOPMENT The synthetic unit hydrograph (UH) method was used to develop the runoff hydrographs for the Bosley Wash basin. DOWL applied the Colorado Plateau UH to the rainfall runoff model of the Bosley Wash detention basin. The following sections describe the Colorado Plateau UH parameters, and the process by which the value for each parameter was determined Colorado Plateau Unit Hydrograph The Colorado Plateau UH requires parameters of area, basin lag time, and unit duration. The USBR Flood Hydrology Manual recommends that the unit duration be equal to the lag time divided by 5.5, rounded down to the nearest 5, 10, 15, or 30 minutes (Aurthur G. Cudworth, 1989). The lag time equation is shown below. L g = 26 K n ( LL ca )N S0.5 \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 17

21 Bosley Wash Detention Basin Hydrology Report Where, Lg = Lag Time, hrs, equal to the time from the center of mass of precipitation to the center of mass of runoff Kn = A trial value based on an estimate of the weighted, by stream length, average Manning s n value for the principal watercourses in the drainage basin L = Length of the watercourse to the hydraulically most distant point, miles Lca = Length measured along L from the point of concentration to a location perpendicular to the watershed centroid, miles S = Watercourse slope, ft/mile N = Exponent = 0.33 Based on a USBR study of 162 flood hydrograph reconstitutions of floods west of the Mississippi, the Flood Hydrology Manual presents guidance on selecting Kn using drainage basin characteristics, such as region, area, and basin factor (i.e., LL ca S 0.5 ). For the Colorado Plateau Region, the USBR Flood Hydrology Manual indicates Kn ranges from to Table 7 of the Guidelines (George V. Sabol, 2008), identifies a minimum Kn of 0.04 for the arid, western Colorado Plateau. Based on discussion with the Colorado DNR Dam Safety Program staff, a Kn value of 0.04 was used for developing the unit hydrograph. Table 8 presents the basin parameters used for application of the Colorado Plateau UH to the Bosley Wash basin; supporting calculations are included in Appendix C. \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 18

22 Bosley Wash Detention Basin Hydrology Report Table 8: Colorado Plateau Synthetic Unit Hydrograph Parameters Unit Hydrograph Parameter Value Basin Area (mi 2 ) L (mi) Lca (mi) S (ft/mile) Kn 0.04 Lg (hr) 0.55 Unit Duration (D) (min) 5 Lg + 0.5D (hr) Unit Hydrograph Result Using a spreadsheet provided by the State of Colorado s Division of Water Resources Dam Safety (State of Colorado DNR), DOWL developed the Bosley Wash detention basin UH. The spreadsheet uses the basin specific parameters described above to compute the UH ordinates, as shown in Figure 9. \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 19

23 DISCHARGE, (cfs) Bosley Wash Detention Basin Hydrology Report 1,800 Unit Inflow Hydrograph Synthetic USBR COLORADO PLATEAU 1,600 1,400 1,200 1, TIME, (Hours) Figure 9: Bosley Wash Synthetic Unit Hydrograph \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 20

24 Bosley Wash Detention Basin Hydrology Report Figure 10: Bosley Wash Basin Parameters Exhibit \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 21

25 3.6 RESERVOIR ROUTING Bosley Wash Detention Basin Hydrology Report The capacity of a reservoir to attenuate an inflow hydrograph is a function of the available storage capacity within the reservoir and the discharge capacity of the spillway. For instance, large reservoirs may have the capacity to store all of an inflow hydrograph, while the majority of an inflow hydrograph may quickly pass through a small reservoir. To account for attenuation through the Bosley Wash Detention Basin, the IDF was routed through the pond using the design stage-storage-discharge relationship of the basin and spillway (excluding the emergency spillway capacity). Because the sole purpose of the proposed Bosley Wash detention basin is for flood control, the pond is assumed to be dry (empty) at the onset of the IDF, and the initial water surface was set to the bottom of the pond, 4,800.0 ft for the reservoir routing simulation (assumes the one foot of sediment in the basin). Additionally, because of the potential for debris to obstruct the low level outlet, the Bosley Wash Detention Basin discharge capacity curve is based only on the principal spillway and the emergency spillway the discharge capacity of the low level outlet is not included in the IDF routings. Table 9 presents the spillway characteristics and Table 10 presents the stagearea-storage-discharge relationships that were incorporated into the HEC-HMS model. Dam Feature Low level outlet (orifice) Table 9: Spillway Crest and Dam Crest Elevations Description Rectangular orifice (42-inches wide by 12- inches high NOT included in the discharge capacity for routing the IDF) 42-ft horizontal weir adjoined by two 21-ft sloping weirs with 2.5H:1V slopes Broad crested trapezoid: 50-ft crest width, 2.5 (left) & 3.0 (right):1 side slopes Elevation (ft) 4,797.0 Principal Spillway Crest 4,806.5 Emergency Spillway Crest 4,811.8 Dam Crest 4,813.5 Table 10 : Bosley Wash Detention Basin - Stage-Area-Storage-Discharge Table Elevation (ft) Area (acres) Storage (ac-ft) IDF Routing Discharge 1 (cfs) \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 22

26 Elevation (ft) Area (acres) Storage (ac-ft) Bosley Wash Detention Basin Hydrology Report IDF Routing Discharge 1 (cfs) 4, , , , , , , , , , , , , , ,416 4, ,830 4, ,951 4, ,6818 4, ,124 1 The IDF routing discharge does not include the discharge capacity of the low level outlet The rating curve for the spillway weir crest was computed using weir equations for each portion of the weir. Flow over the horizontal portion was computed using the equation for a rectangular weir. The horizontal weir was assumed to have 4 contractions, one at each end and corner. Weir coefficients were taken from Table 5-3 of the Handbook of Hydraulics (Brater & King, 1976). Flow over the sloped weir was computed using the equation for a triangular weir, with the weir coefficient taken from Computer Applications in Hydraulic Engineering (Haestad Methods, Inc, 1997). The rating curve for the emergency spillway was developed from a HEC-RAS model, including the approach channel, crest control section, and the downstream section. The energy grade elevation (EGL) at the upstream section (Section 5) over the range of discharge from 25 cfs to 300 cfs was used to define the stage vs. discharge capacity for the emergency spillway; the maximum capacity is 285 cfs, when the pool is up to the dam crest elevation of 4,813.5 ft. The IDF routing discharge capacity of the proposed \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 23

27 Bosley Wash Detention Basin Hydrology Report Bosley Wash detention basin is then the cumulative capacity of the principal spillway weir and the emergency spillway. Spillway discharge capacity worksheets are included in Appendix D. \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 24

28 4.0 RAINFALL RUNOFF MODEL RESULTS Bosley Wash Detention Basin Hydrology Report Model results for the 100-year flood (developed during a previous study) and the IDF routed through the reservoir are presented in Table 11. Simulations were performed for a variety of initial abstraction constants and initial water surface (IWS) elevations (rainfall-runoff hydrographs developed from the Colorado Plateau Unit Hydrograph); complete model results for the IDF simulation are included in Appendix E. Inflow Hyetograph Table 11: IDF & Reservoir Routing Results Peak Inflo w (cfs) Peak Dam Discharg e (cfs) Peak Reservo ir Stage (cfs) Residual Freeboar d (ft) Inflow Volum e (inches ) Effectiv e Precip. (%) 100-year 1, , *Local Storm PMP IA = 0.0 in, IWS = 4,800 ft 1, *Local Storm PMP IA = 0.0 in, IWS = 4,806.5 ft 4,430 2, % Table 11 shows that proposed Bosley Wash Detention Basin will successfully pass the IDF with greater than 1.0 ft of residual freeboard. The HEC-HMS output Time-Series Tables correlating to the simulation summary presented in Table 11 are included in Appendix E. \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 25

29 5.0 REFERENCES Bosley Wash Detention Basin Hydrology Report Aurthur G. Cudworth, J. (1989). Flood Hydrology Manual: A Water Resources Technical Publication. Denver: USBR. Brater, E., & King, H. (1976). Handbook of Hydraulics. George V. Sabol, P. P. (2008). Hydrologic Basin Response Parameter Estimation Guidelines. Tierra Grande Internation, Inc. Haestad Methods, Inc. (1997). Computer Applications in Hydraulic Engineering, 6th Edition. Haestad Methods, Inc. Hansen, E. M., Fenn, D. D., Schreiner, L. C., Stodt, R. W., & Miller, J. F. (1988). Hydrometeorological Report No. 55A. Silver Spring: U.S. Department of Commerce. National Oceanic and Atmospheric Administration. (1984). HMR 49 Probable Maximum Precipitation Estimates, Colorado River and Great Basin Drainages. State of Colorado DNR. (2007). Rules and Regulations for Dam Safety and Dam Construction. Denver: State of Colorado DNR. State of Colorado DNR. (n.d.). Dam Safety Documents. Retrieved 2016, from Colorado Department of Natural Resources: px U.S. Army Corps of Engineers. (1965). EM : Standard Project Flood Determination. U.S. Weather Bureau. (1947). HMR 5 Thunderstorm Rainfall. \\MTJ-FS\Mtj-projects\36\ \95Rpts\IDF\BosleyWash_IDF_R2.docx Page 26

30 APPENDIX A HYETOGRAPHS

31 Bosley Wash Hydrology PMP Calculations HMR 49 - General Storm PMP 24-hr 10mi2 convergence PMP 45.0 % Reduction 6.0 inches Drainage Avg. Orographic Index 3.0 inches 13.3 inches August - greatest PMP depth Convergence factor for effective elevation & barrier considerations CONVERGENCE Procedure Step hours % inches inches % inches inches OROGRAPHIC % inches General Storm TOTAL PMP inches

32 Bosley Wash Hydrology PMP Calculations HMR 49 - Local Storm PMP Avg. 1-hr 1mi2 PMP for drainage 8 inches Elevation adjustment 8 inches No reduction (Bosley Wash Basin's lowest point is below 5000 ft Procedure Step 1/4 1/2 3/ hours % inches % inches inches 60-min increments inches 15-min increments Local Storm Time Sequence Of incremental PMP: Hourly inches 15 Min inches

33 General PMP Hyetographs INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 1 of 15

34 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 2 of 15

35 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 3 of 15

36 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 4 of 15

37 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 5 of 15

38 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 6 of 15

39 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 7 of 15

40 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 8 of 15

41 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 9 of 15

42 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 10 of 15

43 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 11 of 15

44 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 12 of 15

45 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 13 of 15

46 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 14 of 15

47 INPUT DATA Duration 72 hr PRECIPITATION HYETOGRAPH USING CENTER DISTRIBUTION Late Peaking Storm Increment 5 min # increm 864 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) sum \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx General Hyetographs 15 of 15

48 Local PMP Hyetographs INPUT DATA Duration 6 hr HYETOGRAPH USING CENTER DISTRIBUTION EM HMR No. 5 Increment 5 min # increm 72 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) Reorder (inches) (in/hr) z \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx Local PMP Hyetographs 1 of 2

49 INPUT DATA Duration 6 hr HYETOGRAPH USING CENTER DISTRIBUTION EM HMR No. 5 Increment 5 min # increm 72 Interpolated Depth Duration Sorted Data Reordered Data Reordered Data Reordered Data Total Increm. Increm. Increm. Increm. Increm. Duration Depth Change Duration Depth Depth Sort Depth Depth Intensity Depth Intensity Depth Intensity (hrs) (inches) Ratio (hours) (inches) (inches) Order (inches) Reorder (inches) (in/hr) Reorder (inches) (in/hr) Reorder (inches) (in/hr) sum \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ Bosley Wash_Hyetographs.xlsx Local PMP Hyetographs 2 of 2

50 APPENDIX B INFILTRATION WORKSHEETS

51 AREA WEIGHTED K-SAT DETERMINATION FOR BOSLEY WASH BASIN Project No: Project Name: Bosley Wash Calculations by: AEK Checked by: RCR Wtd. Ksat (EQN 1) 0.26 in/hr ΣA i log 10 Ksat i 0.35 Total Area (with reservoir) 1.31 mi 2 OBJECTIDSoil Map Unit (MUSYM) KSat (mm/sec) KSat (In/hr.) Area (mi 2 ) Area*Log 10 (Ksat) Total Equation taken from pg. 53 of Hydrologic Basin Response Parameter Estimation Guidelines by George V. Sabol, PhD, PE \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ BosleyWash_Infiltration.xlsx Bosley Wash Ksat 0-12inches 1 OF 1

52 AREA WEIGHTED K-SAT DETERMINATION FOR BOSLEY WASH BASIN Project No: Project Name: Bosley Wash Calculations by: AEK Checked by: RCR Wtd. Ksat (EQN 1) 0.02 in/hr ΣA i log 10 Ksat i Total Area (with reservoir) 1.31 mi 2 OBJECTIDSoil Map Unit (MUSYM) KSat (mm/sec) KSat (In/hr.) Area (mi 2 ) Area*Log 10 (Ksat) Total Equation taken from pg. 53 of Hydrologic Basin Response Parameter Estimation Guidelines by George V. Sabol, PhD, PE \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Hydrology\ BosleyWash_Infiltration.xlsx Bosley Wash Ksat Table10 1 OF 1

53 APPENDIX C UNIT HYDROGRAPH WORKSHEET

54 COLORADO PLATEAU UNIT HYDROGRAPH 29-Jun-17 Bosley Wash DAMID: dcq Sub-Basin 1 Drainage Area = sq. miles Lg+D/2 = 0.59 Hours Basin Slope = 586 ft./mile Basin Factor = 0.15 L = mi., Length of Watercourse V' = cfs/day Lca = mi., Distance to Centroid Qs = 59.2 * q, cfs Kn = , Ave. Weighted Manning's n PARAMETERS: Calculated: Lag Time, Lg = 0.55 Hours Unit Duration, D = 5.00 minutes Calculated Timestep = 1.78 minutes Data to be used Unit Duration, D = 5 minutes, round down to nearest of 5, 10, 15, 30, 60, 120, 180, or 360 in Analysis Selected Timestep = 2 minutes, integer value evenly divisible into 60 1,800 Unit Inflow Hydrograph Synthetic USBR COLORADO PLATEAU 1,600 1,400 1,200 DISCHARGE, (cfs) 1, TIME, (Hours) UI Record - Unit Graph 2 minute interval UI UI UI UI UI UI UI UI UI UI 7 6 UI UI USBR calculated unitgraph peak = 1711 Interpolated Peak = 1690

55 Time t, % Qs Time t, % Qs of Lg+D/2 Hours Min. q cfs of Lg+D/2 Hours Min. q cfs , , , , , , , , , NOTES : 1. Methodology used Dimensionless Unit Hydrograph. 2. For values of q use Table 4-13 from Flood Hydrology Manual Colorado Plateau UH volume = AF ft3 Total runoff = AF 5.25E+09 in3 Ratio = 1.00

56 APPENDIX D SPILLWAY DISCHARGE WORKSHEETS

57 Water Surface Elevation (ft) Bosley Wash Detention Basin Stage vs. Discharge 4,815 Dam Crest Elevation = 4,813.5 ft 4,813 Emergency Spillway Crest Elevation = 4,811.8 ft 4,811 4,809 4,807 Principal Spillway Crest Elevation = 4,806.5 ft 4,805 4,803 4,801 Orifice Invert Elevation = 4,797.0 ft - Not Included in IDF Routing 4, ,000 1,500 2,000 2,500 3,000 3,500 Discharge (cfs)

58 Bosley Wash Combined Spilway Rating Curve WSEL (ft) Orifice Discharge (cfs) Weirwall Spillway Discharge (cfs) Emergency Spillway (cfs) Combined Discharge (cfs) IDF Routing Emergency + Weirwall Spillway Discharge (cfs) 4, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Outlet Capacity\ Bosley Wash_OutletCapacity_R2.xlsx Combined_R2 Page 1 of 5

59 WSEL (ft) Orifice Discharge (cfs) Weirwall Spillway Discharge (cfs) Emergency Spillway (cfs) Combined Discharge (cfs) IDF Routing Emergency + Weirwall Spillway Discharge (cfs) 4, , , , , , , , , , , ,067 1,127 1,067 4, ,179 1,240 1,179 4, ,296 1,357 1,296 4, ,416 1,478 1,416 4, ,541 1,603 1,541 4, ,670 1,733 1,670 4, ,803 1,866 1,803 4, , ,015 1,951 4, , ,173 2,108 4, , ,353 2,287 4, , ,544 2,478 4, , ,748 2,681 4, , ,964 2,897 4, , ,192 3,125 \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Outlet Capacity\ Bosley Wash_OutletCapacity_R2.xlsx Combined_R2 Page 2 of 5

60 Bosley Wash Orifice Rating Curve Orifice Width: 3.5 ft Orifice Height: 1 ft Orifice Invert Elevation: 4, ft WSEL Orifice Height Orifice h Q = CA 2gh Where: A = Flow area through orifice h = difference between upstream and downstream water levels C = Orifice coefficient Orifice Width Orifice Coefficient: 0.6 (BOR, Design of Small Dams, Figure 10-10, Entrance Condition 1, Series 2) WSEL (ft) Orifice Depth (ft) h (ft) Orifice Area (ft 2 ) Orifice Discharge (cfs) 4, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Outlet Capacity\ Bosley Wash_OutletCapacity_R2.xlsx Orifice Page 3 of 5

61 Bosley Wash Spillway Weirwall Rating Curve 0.5Q Spillway Crest: 4, ft Crest Length, Length, L1 = 30 ft Crest Length, Length, L2 = 6 ft Crest Length, Length, L3 = 6 ft Total Crest Length (L t ) = 42 Crest Side Slope 2.5 H:1V Weir angle, q = 68.2 degrees Number Contractions (N): 4 WSE Q 1 0.5Q V H Weir wall Weir 1 Flow Area Weir 2 Flow Area WSEL (ft) h (ft) L e (ft) Weir Coeff. 1 (C) Weir 1 Discharge (Q 1 ) (cfs) Weir Coeff. 2 (K) Weir 2 Discharge (Q 2 ) (cfs) Weir Wall Discharge (cfs) 4, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,839.3 \\MTJ-FS\Mtj-projects\36\ \26WtrDes\Outlet Capacity\ Bosley Wash_OutletCapacity_R2.xlsx WeirWall Page 4 of 5

62 0.5Q 2 WSEL Weir 1 Flow Area Q 1 0.5Q 2 V Weir 2 Flow Area H Weir wall Diagram WSE V H h L2 L2 h L1 Weir 1 Plan View L1 Weir 1 Side and Front View L3 Q 1 = CL e h 3 2 Where: L e = Effective Crest Length C = Weir coefficient H = Height of water above weir L e = L t 0.1Nh Where: L e = Effective Crest Length L t = Total Crest Length N = Number of contractions H = Height of water above weir Q 2 = K 2g tan θ 2 h5 2 V H θ Weir 2 Side View h WSEL Where: Q = Flow over weir K = Weir coefficient θ = Angle of weir h = Height of water above weir *Multiplied by 2 since there are two identical weirs, one on each side

63