Assessment of Water and Sediment Patterns within Prado Basin

Transcription

1 APPENDIX A Assessment of Water and Sediment Patterns within Prado Basin APPENDIX A Submitted To: Orange County Water District Ward Street Fountain Valley, California USA Submitted By: Golder Associates Inc. 44 Union Boulevard, Suite 300 Lakewood, Colorado USA Distribution: Orange County Water District HDR Engineering November 19, 2010 Project No A world of capabilities delivered locally Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation

2 November 2010 i Table of Contents 1.0 INTRODUCTION ANALYSIS Sediment Yield Recent Sedimentation in Prado Basin Sediment Yield Distribution of Sediment Sizes Channel Location Flow Conditions in Prado Basin Model Flow Conditions without and with V shaped Alignment Velocity Profiles CONCLUSIONS REFERENCES List of Tables Table A-1 Comparison of Sediment Yield Estimates Table A-2 Average Sedimentation Rates Table A-3 Six Modeled Flow Rates from Flow Scenarios and Maximum Flow Table A-4 Average Hydraulic Conditions in Ponded Area in Prado Basin at WSE of 510 ft for Flow Scenarios with and without SAR Only Table A-5 Average Hydraulic Conditions in Area at WSE of 510 ft for Flow Scenarios with and without SAR Only Table A-6 Average Hydraulic Conditions in Ponded Area in Prado Basin at WSE of 498 ft for Flow Scenarios with and without SAR Only Table A-7 Average Hydraulic Conditions in Area at WSE of 498 ft for Flow Scenarios with and without SAR Only List of Figures Figure A-1 Alignments in Prado Basin Figure A-2 Historic Sedimentation from 1988 to 2009 Figure A-3 Historic Sedimentation from 1988 to 2009 and s Figure A-4 Potential Optimized Alignment (version 1) Figure A-5 MIKE21C Model Area Figure A-6 Predicted Water Depths in Prado Basin for 47,800cfs and WSE of 510ft without s Figure A-7 Predicted Water Depths in Prado Basin for 47,800cfs and WSE of 510ft with SAR Only Figure A-8 Predicted Water Depths in Prado Basin for 47,800cfs and WSE of 510ft without s ( Alignments shown for reference only) Figure A-9 Predicted Flow Velocity Vectors in Prado Basin for 5,000 cfs and WSE of 510 ft near SAR and Prado Dam without s. (Note: SAR Only alignment in red outline for reference only.)

3 November INTRODUCTION The project goal is to evaluate augmentation of the sediment load in the Santa Ana River by removing deposited sediment from the Prado Basin and introducing it into the Santa Ana River. This appendix addresses some of the potential project effects on the Prado Basin. To address the following questions, Golder Associates, Inc. (Golder) analyzed hydraulic conditions and sediment deposition patterns within the Prado Basin; and estimated sediment yield from the catchment. The principal questions to be addressed are as follows: 1. Will the sediment transport capacity of the water flowing in the vicinity of the dredging trench change once dredging operations has commenced, and how will such a change impact future depositional patterns of sand/silt/clay? 2. What is the rate of sedimentation in the dredging trench and is there an opportunity to optimize its location? 3. Will the anticipated flow velocities and flow velocity directions change post-dredging and grubbing and how might it impact potential floating debris movement? 4. Will there be upstream headcut movement post-dredging and how might it affect operations and the environment? Figure A-1 illustrates the alignments of possible dredging channels currently under consideration for this project. They are the Chino Creek, Temescal Creek and Santa Ana River (SAR) ( V shaped), and Santa Ana River (SAR Only) alignments. Golder performed the preliminary computer simulation to estimate the effects of the project on Prado Basin where the preferred alternative is deemed to be the SAR Only alignment, as identified on Figure A-1. The final selection of a preferred alignment might change. Currently the SAR Only alignment, which could be further optimized, is deemed as the preferred alternative. The results presented in this Appendix are based on computer simulation and analysis of historic data relevant to the Prado Basin. Interpretation of potential effects of the proposed project on Prado Basin requires estimates of the sediment discharge into the basin, of the spatial distribution of deposited sediment, of the spatial distribution of sediment deposition rates, and of the potential effects of dredging on hydraulic conditions within the basin. The knowledge regarding the spatial distribution of deposited sediment and its rate of deposition is required to estimate the rate of sediment deposition in the dredging channel and to optimally locate it. The dredging channel should preferably be located in a region where the greatest amounts of deposited sediment and the highest rates of sedimentation occur. Estimates of the rate of sediment discharge into the basin are required to cross-checks replenishment rate estimates.

4 November Analyses of the hydraulic characteristics of flow in the basin are required to assist in the interpretation of potential debris movement and in the interpretation of the anticipated geomorphic response to the dredging operations. The geomorphic response of the basin will determine whether a headcut will form and whether changes in the spatial distribution of deposited sand, silt, and clay will occur due to the presence of dredging operations. A MIKE21C model was developed to assess hydraulic conditions within Prado Basin, with and without the SAR Only dredging alignment. MIKE 21C is modeling software that can be used to simulate water and sediment flow. The hydraulic performance of other alignments has not been fully assessed. Once the location of the preferred dredging channel has been decided the MIKE 21C model can be focused on investigating its effect on the hydraulic response of flow within Prado Basin. At this stage of the investigation the focus has shifted from the V shaped dredging channel to the SAR Only alignment. In addition to computer simulation, Golder uses professional judgment and existing site knowledge to address critical questions (listed above) regarding the SAR Only alignment.

5 November Figure A-1 Alignments in Prado Basin

6 November ANALYSIS 2.1 Sediment Yield The sediment yield from the Santa Ana River catchment upstream of Prado Dam, where the greatest amount of sediment flowing into Prado Dam originates, is estimated by analyzing recent sediment deposition in the Prado Basin and comparing it with estimates previously executed by the US Army Corps of Engineers (USACE) and others Recent Sedimentation in Prado Basin The two most recent surveys of the Prado Basin occurred in 1988 and A comparison between the 2009 LiDAR survey and the 1988 bathymetric survey was made to estimate the distribution of deposited sediment within Prado Basin. The result is shown in Figure A-2, which confirms that the major source of sediment flowing into the Prado Basin originates from the SAR. The shape of the deposited sediment originating from the SAR principally assumes a delta or fan-type pattern. The layers of deposited sediment are thickest in the delta reach, and become increasingly thinner towards the dam. The sediment originating from Temescal Creek is characterized by a similar deposition pattern, although it contains much smaller amounts of sediment. Based on the difference between the 2009 and the 1988 surveys Golder estimates an average sedimentation rate in Prado Basin of about 1.15 million yd 3 /yr over 21 years Sediment Yield Sediment yield is the quantity of sediment that is transported through a drainage basin or watershed over a period of time. It is usually expressed as the mass of material per unit area of the upstream drainage basin per unit time (e.g. metric tons per square kilometer per year). This convention of expressing sediment yield is also known as the specific sediment yield. All specific sediment yield values presented in this section is summarized in Table A-1 using both imperial and SI units. Based on the analysis referred to in the previous section, it is estimated that the specific sediment yield of the SAR upstream of Prado Basin equals 261 metric t/km 2 /yr. Sediment yield for the Santa Ana River upstream from the Prado Dam has been calculated at different times by the U.S. Army Corps of Engineers (USACE 1967, 2003, 2005); by the U.S. Interagency Advisory Committee on Water Data, Subcommittee on Sedimentation (1992); and by Warrick and Rubin (2007). In order to convert the estimates of the different studies to a common basis specific sediment yield is expressed in metric t/km 2 /yr. This estimate is based on the assumption that the porosity of the deposited sediment is 40%, i.e. a bulk density of 1,400 kg/m 3 is assumed, and that the estimated trap efficiency of Prado Dam is 97%. Trap efficiency expresses the effectiveness of a reservoir to trap sediment. In this

7 November case it means that Prado Dam traps 97% of the sediment discharging into it. The estimated specific sediment yields from the different studies are summarized in Table A-1. The USACE (1967) estimate is the lowest, set at 113 metric t/km 2 /yr. Several other sedimentation rates reported by the USACE in their 2005 report result in sediment yield rates that are significantly higher than those from their 1967 report. It ranges between 211 and 303 metric t/km 2 /yr. The Warrick and Rubin (2007) estimate, when converted to specific sediment yield, amounts to 350 metric t/km 2 /yr. The Subcommittee on Sedimentation of the U. S. Interagency Advisory Committee on Water Data (1992) reports a sedimentation rate in the Prado reservoir that converts to a sediment yield rate of 255 metric t/km 2 /yr. A report published in 2002 by the Department of Boating and Waterways and State Coastal Conservancy entitled California Beach Restoration Study by the Department of Boating and Waterways and State Coastal Conservancy reports the sedimentation rate from 1979 to 1988 to be at least 1,380,000 yd 3 /yr as stated by Chief of the Reservoir Regulation Section of the US Army Corps of Engineers Los Angeles District. This sedimentation rate results in a specific sediment yield of 312 metric t/km 2 /yr. The summary in Table A-1 indicates that the USACE (1967) estimate is likely on the low side. The remainder of the estimates varies between about 200 and 350 metric t/km 2 /yr, which indicates that the estimate made for this study, i.e. 260 metric t/km 2 /yr, is reasonable. Note that the commissioning of Seven Oaks Dam in the Santa Ana River watershed in 1999 will likely decrease the future sediment load to Prado Basin.

8 November Table A-1 Comparison of Sediment Yield Estimates Source Reported Sedimentation Rate m 3 /yr ( m 3 /yr m 3 /yr) Notes Annual Sedimentation Rate 10 6 m 3 /yr yd 3 /yr Specific Sediment Yield metric ton/ (km 2 yr) Historic surveys (1960, 1975, USACE (2003) 1988) ,212, acre-feet/yr Estimated for 1956 to , acre-ft/yr Average annual sediment USACE (2005) (700 to 709 acre-ft/yr) deposition rates for after ,129, Warrick and Rubin (2007) 10 6 m 3 /y Estimated for 1968 to ,307, ,000,000 yd 3 Golder estimate from 1988 and Golder Analysis (This Study) over 21 years 2009 surveys ,154, Estimate based on difference USACE (1967) 5880 acre-ft/18.9 yr from 1941 to , US Interagency Advisory Committee on Water Data, 1941 to 1979 Average of three Subcommittee on Sedimentation (1992) 1,130,000 yd 3 /yr surveys ,130, Department of Boating and Waterways and State Coastal Conservancy 1,380,000 yd 3 /yr 1979 to ,380,

9 November Figure A-2 Historic Sedimentation from 1988 to 2009

10 November Distribution of Sediment Sizes The available sediment sampling data is not extensive enough to map sediment types within the basin. However, based on experience, it is deemed reasonable to expect that the deposited sediment in the vicinity of the River Road Bridge primarily consists of sand, which then transitions to silty sand as the SAR approaches the sparsely vegetated area behind Prado dam. Silts and clays deposit within the sparsely vegetated pond area immediately upstream of Prado dam Channel Location The ideal location of the dredging channel location can be determined by making use of the sediment distribution patterns identified in the foregoing sections. The currently proposed locations of the dredging channel alternatives relative to sediment deposition thickness are shown in Figure A-3. It is noted that the Chino Creek dredging channel is located in an area with relatively low sediment deposition rates. Similarly, the Temescal Creek dredging channel alternative is not optimally located. Although the SAR Only alignment is located in a region with greater sediment thicknesses, it is noted that it is not optimally located. Figure A-4 illustrates that the analysis results pertaining to sedimentation can be used to optimally locate the dredging channel. The differences between sedimentation rates for the alternative dredging channel locations are shown in Table A-2. The table illustrates that it is possible to optimize the location of the dredging channel. The potential optimized alignment (version 1) is associated with a 30% greater sedimentation rate than the currently proposed SAR Only location. It is recommended that additional analyses be conducted to identify the preferred dredging channel location. Table A-2 Average Sedimentation Rates Project Element Average Sedimentation Volume Rate ft 3 yd 3 % ft 3 /yr yd 3 /yr Volume Prado Basin 654,490,000 24,240, % 31,166,190 1,154,303 "V" Shaped 10,817, , % 515,129 19,079 SAR Only 15,108, , % 719,438 26,646 Chino Creek 8,104, , % 385,947 14,294 Potential Optimized Alignment v1 20,377, , % 970,367 35,940

11 November Figure A-3 Historic Sedimentation from 1988 to 2009 and s

12 November Figure A-4 Potential Optimized Alignment (version 1)

13 November Flow Conditions in Prado Basin The dredging scenario evaluated during this analysis considered conditions with and without the SAR Only dredging alignment. The SAR Only dredging alignment starts at the junction of the SAR and Temescal Creek and continues 6,000ft upstream the SAR. The channel width is 200ft. The goal of the hydraulic analysis was to identify possible flow changes with the SAR Only dredging alignment in place Model A MIKE21C model has been developed for Prado Basin to aid in evaluating hydraulic conditions for 6 flow scenarios with respect to the dredging proposal. MIKE21C is a two-dimensional curvilinear hydraulic and sediment transport model developed by the Danish Hydraulic Institute (DHI). The curvilinear grid can follow an irregular boundary more accurately than models using rectilinear girds. The model incorporates Prado Basin from Prado Dam (the downstream boundary) to River Road Bridge (the upstream boundary), where it crosses the SAR (Figure A-5). Two operating water surface elevations of Prado Basin, 510 ft and 498 ft, establish the downstream boundary condition. The operating water surface elevation at 510 ft is the maximum operating water surface elevation for Prado Basin based on available operation records. The maximum water surface elevation was used in order to evaluate the maximum area that may potentially be inundated within Prado Basin. The operating water surface elevation at 498 ft is the normal operating level based on guidance from the OCWD.

14 November Figure A-5 MIKE21C Model Area The model was configured to simulate conditions within Prado Basin, assuming incoming flow from the SAR. Incoming flows from other sources (e.g. Temescal and Chino Creeks) are not included at this time. This is deemed a reasonable assumption because the largest portion of the sediment flowing into the Prado Basin originates from the SAR. Data for flows into the reservoir were not available prior to development of this model at this stage. Therefore, historical, daily flow data for the period 1980 to 2010 from the USGS flow gage, located downstream of Prado Dam, was used to determine flow magnitudes. Golder is aware that flows downstream of the dam would likely be lower than incoming flows. However, the flow range downstream of the dam was deemed to provide some indication of flow magnitudes that should be considered.

15 November Historical discharges downstream of the dam typically range between 100cfs and 5,000cfs, although higher flows have been reported. At this stage of the investigation it was decided to set the minimum flow at 250cfs. This selection will be re-considered during the final stages of the project. Four additional discharges between 100cfs and 5,000cfs were also considered; i.e. 500cfs, 750cfs, 1,250cfs, and 2,000cfs (Table A-3). A maximum flood magnitude at 47,800 cfs was also included. This is the maximum flood incoming from the SAR to Prado Basin in the period of record for USGS gage Santa Ana River at Metropolitan Water Dsictrict Crossing, near Arlington, CA. Table A-3 Six Modeled Flow Rates from Flow Scenarios and Maximum Flow Scenario Discharge cfs cfs cfs 4 1,250 cfs 5 2,000 cfs 6 5,000 cfs Maximum Flow 47,800 cfs In the absence of field-surveyed hydraulic conditions throughout the basin, hydraulic roughness was estimated using aerial imagery and field observations. In the open pond area near Prado Dam, as well as in the active river channel, the range of Manning s n values was set at to In the overbank areas the selected Manning s n values range from to Impoundment ponds located at the north-central side of the basin were excluded from the model. Sufficient model stability was achieved at a general time step of two seconds. At this point in time of the investigation the working model has not been fully developed into a coupled hydraulic/sediment transport model but can be implemented if necessary for further design Flow Conditions without and with V shaped Alignment Comparison of the flow conditions before and after introduction of the alterative dredging area shows insignificant hydraulic changes during maximum operating water surface elevations (Table A-4). Figure A-6 and Figure A-7 show the flow depths for the highest simulated flow rate (47,800cfs) for conditions with and without the proposed SAR Only dredging alignment. The average bed shear stress and flow velocities in the ponded area behind Prado Dam shows minimal change between the two scenarios for both operating pond conditions (Table A-4 and Table A-6). The reason for this is that the shear stress is a function of both the water depth and energy slope. The energy slope in the pond area is low, which greatly influences the magnitude of the shear stress. Flow velocities in the pond area are low and large changes for conditions with and without the dredging area are not anticipated.

16 November The flow depth within the dredging area is deeper when dredging is present than without, as expected. Average trench depth is 12.3ft with average flow depth in the dredging trench of 19 ft and 8.5 ft for modeled operating pond conditions of 510ft and 498ft, respectively (Table A-5 and Table A-7). The assessment of the hydraulics within the dredging area under higher pond conditions at 510ft indicates minimal change in flow velocities with lower bed shear stresses than without dredging (Table A-5). Bed shear stresses rise above psf (approximately critical shear stress for coarse sand) for all scenarios without dredging (Table A-5 and Table A-7). However, for the dredging scenario under the higher pond elevation of 510ft, the critical shear stress for coarse sand is on exceeded for discharge scenarios at 1,250cfs and lower. This suggests that sand-size sediment would drop out of the water column and be trapped by the flooded dredging areas to a greater degree than without dredging under the higher pond elevation. For the lower normal pond elevation at 498ft, bed shear stresses are marginally higher with dredging than without, suggesting similarity in depositional characteristics such as grain size and volume in the dredging area with or without dredging. The three alternative dredging areas are illustrated for reference over the water depths for the case without dredging in Figure A-8. Other dredging alignments or portions thereof similar to the SAR Only alignment that extend beyond the pond area and contain incoming flow are likely to experience increases in flow velocities and bed shear stress when the buffering effect of the ponded water is not available. At this time, the working model has not been fully developed into a coupled hydraulic/sediment transport model with all dredging alternatives and the presented results are for initial general assessment only. Scenario Discharge Table A-4 Average Hydraulic Conditions in Ponded Area in Prado Basin at WSE of 510 ft for Flow Scenarios with and without SAR Only Average Water Depth (ft) Average Flow Velocity (ft/s) Average Bed Shear Stress (psf) Without With Without With Without With 250 cfs cfs cfs ,250 cfs ,000 cfs ,000 cfs ,800 cfs

17 November Scenario Discharge Table A-5 Average Hydraulic Conditions in Area at WSE of 510 ft for Flow Scenarios with and without SAR Only Average Water Depth (ft) Average Flow Velocity (ft/s) Average Bed Shear Stress (psf) Without With Without With Without With 250 cfs cfs cfs ,250 cfs ,000 cfs ,000 cfs ,800 cfs Scenario Discharge Table A-6 Average Hydraulic Conditions in Ponded Area in Prado Basin at WSE of 498 ft for Flow Scenarios with and without SAR Only Average Water Depth (ft) Average Flow Velocity (ft/s) Average Bed Shear Stress (psf) Without With Without With Without With 250 cfs cfs cfs ,250 cfs ,000 cfs ,000 cfs ,800 cfs Scenario Discharge Table A-7 Average Hydraulic Conditions in Area at WSE of 498 ft for Flow Scenarios with and without SAR Only Average Water Depth (ft) Average Flow Velocity (ft/s) Average Bed Shear Stress (psf) Without With Without With Without With 250 cfs cfs cfs ,250 cfs ,000 cfs ,000 cfs ,800 cfs

18 November Figure A-6 Predicted Water Depths in Prado Basin for 47,800cfs and WSE of 510ft without s

19 November Figure A-7 Predicted Water Depths in Prado Basin for 47,800cfs and WSE of 510ft with SAR Only

20 November Figure A-8 Predicted Water Depths in Prado Basin for 47,800cfs and WSE of 510ft without s ( Alignments shown for reference only)

21 November Potential changes to flooding patterns were also evaluated for the highest flow scenario (47,800cfs) simulated concurrently with the maximum reported operating water surface elevation of 510 ft for the period December 10, 2009 to March 10, The downstream boundary condition was set at the constant maximum reported operating water surface elevation, which assumes that dam operations are such that the water surface elevation is maintained. This is deemed a conservative approach to assessing flood potential upstream of Prado Dam. Comparison of the flooding extents for the highest flow scenario of 47,800cfs, before and after the introduction of the alterative dredging area, shows insignificant changes in the flooding pattern beyond higher flow depth in the dredged channel, as would be expected. The elevation changes are so small that they are hardly measurable, and are therefore not presented. Similar results were seen for the other flow scenarios including 5,000 cfs. The flooding water depths at the reservoir for the highest flow scenario without and with the SAR Only alternative are shown in Figure A-6 and Figure A-7, respectively Velocity Profiles Velocity vectors resulting from the MIKE21C model without dredging are illustrated in Figure A-9. These velocity vectors illustrate the direction water is flowing by the direction of the arrow as well as the relative magnitude of the velocity by the length of the arrow line. The general direction of flow from the SAR is towards the dam including the outlet on the east side of the dam. However there are a few vectors located directly north of the dam that cannot be explained at this time. Flow velocity and direction will be further evaluated during the continued MIKE21C modeling.

22 November Figure A-9 Predicted Flow Velocity Vectors in Prado Basin for 5,000 cfs and WSE of 510 ft near SAR and Prado Dam without s. (Note: SAR Only alignment in red outline for reference only.)

23 November CONCLUSIONS The objective for this technical memorandum is to address four questions concerning the proposed dredging in Prado Basin. As noted earlier, to date, Golder assessed the SAR Only alignment (Figure A- 1). Preliminary assessments indicate that the SAR dredging alignment may be preferred as it could yield more sediment than the Chino Creek and V Shaped alignments. This alignment is therefore focused upon. Computer model results and professional judgment, based on site knowledge, have been used to develop responses to the key questions. 1. Will the sediment transport capacity of the water flowing in the vicinity of the dredging trench change once dredging operations has commenced, and how will such a change impact future depositional patterns of sand/silt/clay? The models reveal that average velocities do not change significantly in the SAR Only alignment during maximum and normal operating levels. Bed shear stresses are slightly lower for lower discharges at maximum operating levels when dredging is introduced. This is because the ponded water behind the dam essentially buffers against large changes in flow velocity and shear stress in the dredging alignment. However, the SAR dredging alignment extends beyond the pond area (Figure A-8), which under normal operating levels results in incoming flow experiencing increases in bed shear stress, especially under higher discharges. This is because the buffering effect of the ponded water is not present. Based on our professional judgment, the project team is of the opinion that: The SAR alignment will impact sediment movement due to higher bed shear stresses in the portion of the dredging trench outside of the ponded area at normal operating levels. The increased bed shear stress may move sands and suspended silts and clay further to the west. The dredged SAR trench will have an increased sediment carrying capacity, i.e. hold more water, relative to the non-trenched channel in the portion outside the ponded area. During normal operating levels, this may decrease the amount of water on the floodplain. This means more sediment may be delivered to the dredging trench relative to the floodplain than under current conditions. 2. What is the rate of sedimentation in the dredging trench and is there an opportunity to optimize its location? The assessment reveals that the location of the dredging trench may be optimized. An example is shown in Figure A-4, which provides greater sediment replenishment rates, and greater amounts of sediment that may be dredged. 3. Will the anticipated flow velocities and flow velocity directions change post-dredging and grubbing and how might it impact potential floating debris movement?

24 November Figure A-9 illustrates the velocities modeled in MIKE21C without dredging and indicates that flow from the SAR area is directed towards the dam and outlet. For maximum operating levels of the water surface elevations, the SAR Only alignment minimally altered velocity. However, the portion of the SAR Only dredging alignment that extends beyond the pond area and contains incoming flow does show increases in bed shear stress under normal operating conditions because the buffering effect of the ponded water is not present. Based on professional judgment, we predict that during normal operating levels the bed shear stress in the SAR Only dredging trench will increase in magnitude in the portion above the ponded area. This may funnel the movement of floating debris through this area. This offers an opportunity to capture floating debris in a specific location and install equipment to remove the sediment. The project team recommends that the trees adjacent to the dam remain intact. This will offer the same buffer to floating debris as the current operating conditions. 4. Will there be upstream headcut movement post-dredging and how might it affect operations and the environment? Under the maximum ponded water surface elevation conditions behind the dam, the SAR Only dredging alignment modeled indicate minimal changes in flow velocity and bed shear stress. However, the project team expects these conditions will differ for the SAR Only alignment during normal operating conditions. It is our professional opinion that: Due to the fact that SAR trench will be above the ponded water line during normal operating conditions, there will be an alteration to the bed shear stresses and a headcut will form. This headcut will effectively increase the sediment transport rate into the basin. The rate of head-cut movement will depend on incoming flow rates and sediment load, final geometry of the dredged trench, incoming sediment load, and materials encountered during headcut migration. The high incoming sediment load to the basin will counteract the impact of headcut migration including rate of movement. The project team does not anticipate a detailed assessment of headcut formation/migration during the final phases of this project. The amount of data and intensity of the calculations are beyond the scope of work at this time. We recommend headcut migration be monitored during the demonstration project and in the months/years following the dredging.

25 November Sincerely, GOLDER ASSOCIATES INC. Ian Dubinski, Ph.D. Senior Fluvial Geomorphologist George W. Annandale, D.Ing., P.E. Principal ID/GWA/rjg

26 November REFERENCES Department of Boating and Waterways and State Coastal Conservancy California Beach Restoration Study. Sacramento, California. Dietrich, W.E., D.G. Bellugi, L.S. Sklar, J.D. Stock, A.M. Heimsath, and J.J. Roering Geomorphic Transport Laws for Predicting Landscape Form and Dynamics. Prediction in Geomorphology Geophysical Monograph Griffiths, P.G., R. Hereford, and R.H. Webb, Sediment yield and runoff frequency of small drainage basins in the Mojave Desert, U.S.A.: Geomorphology Hjulstrom, Filip Studies of the Morphological Activity of Rivers as Illustrated by the River Fyris. Bull. Geol. Inst. University of Upsala, Vol. XXV, Leopold, L.B., M.G. Wolman, and J.P. Miller Fluvial Processes in Geomorphology. Dover Publications, Inc. New York. Subcommittee on Sedimentation Sediment Deposition in U.S. Reservoirs: Summary of Data Reported Reston, Virginia: U. S. Interagency Advisory Committee on Water Data. U.S. Army Corp of Engineers Interim Water Control Plan (During Construction). Prado Dam and Reservoir, Santa Ana River, Orange County, California. U.S. Army Corp of Engineers Prado Basin Water Conservation Feasibility Study, Prado Dam, Riverside and San Bernardino Counties, California. U.S. Army Corps of Engineers Sedimentation Studies for Prado Flood Control Reservoir, Santa Ana River Basin, and Orange County, California. Warrick, J.A., and D.M. Rubin, Suspended-sediment rating curve response to urbanization and wildfire, Santa Ana River, California. Journal of Geophysical Research, Vol. 112.

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