2-DIMENSIONAL HYDRAULIC MODELING FOR … · INTRODUCTION ... System and to provide hydraulic parameters for the design of the bank armor. Two models were included in the project scope

2-DIMENSIONAL HYDRAULIC MODELING FOR PUMPING PLANT PROTECTION AND RIPARIAN RESTORATION AT THE LLANO SECO UNIT ON THE SACRAMENTO RIVER NEAR RM 178 – SUPPLEMENTAL DESIGN REPORT

GLENN AND BUTTE COUNTY, CALIFORNIA

June 3, 2010

Prepared for:

580 Vallombrosa Avenue Chico, CA 95926

Sacramento River Looking Upstream at Left Bank near River Mile 178

2-DIMENSIONAL HYDRAULIC MODELING FOR PUMPING PLANT PROTECTION AND RIPARIAN RESTORATION AT THE LLANO SECO UNIT ON THE SACRAMENTO RIVER NEAR RM 178 – SUPPLEMENTAL DESIGN REPORT

GLENN AND BUTTE COUNTY, CALIFORNIA

June 3, 2010

Prepared for:

580 Vallombrosa Avenue Chico, CA 95926 Prepared by:

2150 River Plaza Drive, Suite 330 Sacramento, CA 95833 (916) 563-7700 Project Number 33-0579.00

2-Dimensional Hydraulic Modeling i Ayres Associates Inc For Pumping Plant Protection and Engineers/Scientists/Surveyors Riparian Restoration at the Llano Seco Unit Sacramento, CA on the Sacramento River, Glenn & Butte County, CA June 3, 2010

TABLE OF CONTENTS

1. INTRODUCTION ............................................................................................................. 1 1.1 Overview................................................................................................................... 1 1.2 Acknowledgments..................................................................................................... 1 1.3 Project Area .............................................................................................................. 1 1.4 Background............................................................................................................... 3 1.5 Project Scope ........................................................................................................... 5

2. UPDATES TO HYDRAULIC MODEL FROM PHASE I REPORT.................................... 6 2.1 Updates to the Phase I Two-Dimensional Hydraulic Model...................................... 6 2.2 History of Original Hydraulic Model .......................................................................... 6 2.3 Refinement and Land Use Changes......................................................................... 6 2.4 Channel Realignment ............................................................................................... 6

3. HYDRAULIC MODEL RUNS ........................................................................................... 7 3.1 Existing Conditions – 2008 Land Use Hydraulic Model Run .................................... 7 3.2 Project Conditions – Bank Armor, Bank Armor Removal and Riparian Restoration Hydraulic Model Runs ......................................................................................................... 7

4. HYDRAULIC MODELING ................................................................................................ 7 4.1 General ..................................................................................................................... 7 4.2 Model Development.................................................................................................. 8 4.3 Boundary Conditions .............................................................................................. 10

5. HYDRAULIC MODELING RESULTS............................................................................. 10 5.1 Existing Conditions – 2008 Land Use Hydraulic Model Runs................................. 10 5.2 Project Conditions – Bank Armor, Bank Armor Removal and Riparian Restoration Hydraulic Model Runs ....................................................................................................... 11

6. CONCLUSIONS............................................................................................................. 12 7. REFERENCES .............................................................................................................. 13

2-Dimensional Hydraulic Modeling 1 Ayres Associates Inc For Pumping Plant Protection and Engineers/Scientists/Surveyors Riparian Restoration at the Llano Seco Unit Sacramento, CA on the Sacramento River, Glenn & Butte County, CA June 3, 2010

1. INTRODUCTION 1.1 Overview This report summarizes the results from a 2-dimensional hydraulic model analyzing several elements of one proposed project on the Sacramento River near River Mile (RM) 178 and on the Llano Seco Ranch. The elements include riparian restoration in the floodplain, armor bank protection in one area to maintain channel alignment near diversion, and bank armor removal in another area to allow natural river meander and cutoff processes. US Fish and Wildlife Service and Princeton Codora Glenn and Provident Irrigation Districts have proposed to convert approximately 500 acres of grassland/cropped land in the floodplain area adjacent to the river to riparian habitat and also to arrest the rapid bank erosion and subsequent river migration on the left bank in the area of River Mile (RM) 178 by the installation of armor. The primary purpose of the armor is to prevent the river migration pattern from completely bypassing the irrigation pumping plant at RM 177.6 Right, which serves Provident Irrigation District and Princeton Codora Glen Irrigation District. The procedures, methodologies and boundary conditions used to accomplish this modeling are outlined in the following sections of this report. This report is a supplement to previous analyses conducted by Ayres Associates (2005) that showed that riparian vegetation restoration, bank armor modifications, and cutoff channel would achieve project goals without adversely impacting the Sacramento River Flood Control System. The purpose of this project was to update the hydraulic modeling with recent channel bathymetry and land use conditions so the most current available information can be used for bank protection design. The updated modeling was also checked to confirm that impacts to the flood control system are negligible. 1.2 Acknowledgments The hydraulic modeling of these project features was performed for River Partners under a contract agreement by Ayres Associates, Sacramento, California Office. Helen Swagerty, Senior Restoration Biologist, is the Project Manager for River Partners. 1.3 Project Area The project area encompasses a portion of the Sacramento River between Glenn and Ord Bend, California. Figure 1 shows the project location and extent of the hydraulic modeling. The hydraulic model includes the Sacramento River and the Butte Basin overflow area at the downstream boundary, the flow split area and the combined flow area upstream of the project.


Figure 1 – Project Location and Hydraulic Modeling Limits

Project Area

2D Model

1 1 1 1 1

1 1 1 1 2

1 1 1 1 3

1 1 1 1 4

1 1 1 1 5

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1.4 Background The project area is located near RM 178 on the Sacramento River. This particular reach of the Sacramento River has a natural overflow that conveys flood waters into the Butte Basin which is located toward the southeast from the project site. The flood control levee on the east side of the river begins near the downstream end of the model (approximately at RM 176). The floodplain on the west bank of the river in the project reach is contained by the flood control levee, which begins upstream at approximate RM 184. The recommended use of stone armor on the eroding bank was based on a joint recommendation from the USF&W Service Refuge and representatives of the two affected irrigation districts in regards to an alternative study in Phase I of this project (River Partners Communication, 2010). There was general agreement that the “Traditional Riprap Revetment and Allow the River Bend to Cutoff” alternative from the Phase I Report (Ayres 2005) was preferred for meeting both goals of restoring habitat on the Refuge and the long term protection of the Pumping Plant. The area designated for restoration is located adjacent to the river on the east side, between RM 176 and 178, and the location of the proposed bank protection is on the left bank of the river just downstream of RM 178 on the inside (convex) bank. These features are shown on Figure 2, superimposed on an aerial image from 1998. Figure 3 shows the upstream features, which include stone removal to promote a natural cutoff and realignment of the channel. Photograph 1 shows a view of the eroding left bank area on the River where armor protection is planned.

Photograph 1 – Looking Upstream at the Eroding River Bank at RM 178 Left


Figure 2 - Location of Project Features on 1998 Aerial Image.


Figure 3 - Location of Project Features on 1998 Aerial Image.

1.5 Project Scope The purpose of this project is to update the Ayres (2005) analysis to confirm that the combination of the proposed riparian habitat restoration plantings and bank armoring will not have any detrimental effects on the hydraulics of the Sacramento River Flood Control System and to provide hydraulic parameters for the design of the bank armor. Two models were included in the project scope. The report summarizes the processes and results from the following tasks:

Refine and update the existing conditions hydraulic model from the Phase I Report – This task included updating the previously developed 2-dimensional hydraulic model from the Phase I portion of this project (Ayres, 2005) with bathymetry and topography obtained in June 2008 (Ayres 2008) and added the newly installed bank protection at RM 177.8R installed by the Corps of Engineers in the fall of 2008.


Modify the new existing conditions model with the proposed project – Include the proposed bank protection features, the riparian plantings in the floodplain, and removal of the existing rock armor at RM 178.5 Right.

Compare the proposed project runs with the existing conditions runs for changes in

hydraulic conditions - The two sets of models will be compared for any adverse hydraulic impacts.

2. UPDATES TO HYDRAULIC MODEL FROM PHASE I REPORT 2.1 Updates to the Phase I Two-Dimensional Hydraulic Model The hydraulic model from the Phase I Report (Ayres 2005) was used as the base model for this study. That model was updated with new bathymetry and bank line data (Ayres 2008) and also the geometry of the new bank armor installed by the Corps in the fall of 2008. The limits of the new model are now from RM 173 to RM 183. These new limits and topography become the baseline model geometry for existing condition runs. 2.2 History of Original Hydraulic Model The original 2-D hydraulic model for the Butte Basin, developed in 1995 for the US Army Corps of Engineers (USACE), was used as the basis for this modeling, (with permission from the Corps). That model was originally developed to aid in analyzing the effects on the overflow weirs (flood relief structures or FRS) from a series of potential river bend cutoffs in the area of the FRS’s. That original model extended from RM 173 to 194 on the Sacramento River and included inflows from two smaller drainages, Stoney Creek and Big Chico Creek. The model also included three overflow weirs and they are designated as, M&T FRS, 3-B’s FRS, and the Goose Lake FRS. 2.3 Refinement and Land Use Changes The biggest change made to the original model was the refining of elements and element size. Most of the elements in the overbank and channel were split into smaller elements. In the area of greatest concern (the bend at RM 178) the elements were refined even more to get an accurate depiction of the movement and velocity of the river flow. Land uses were reviewed from the Phase I model and updated where necessary to reflect the 2008 conditions. 2.4 Channel Realignment The alignment of the Sacramento River has been altered somewhat since the 1995 topographic mapping due to erosion, sedimentation and bend migration. While, the entire reach has not been resurveyed, the area between RM176 and RM 183 was resurveyed in 2008 (Ayres, 2008) for bathymetry and where the overbank has changed, those areas were also resurveyed. This recent mapping has been incorporated into the updated model geometry.


3. HYDRAULIC MODEL RUNS 3.1 Existing Conditions – 2008 Land Use Hydraulic Model Run The existing conditions hydraulic model represents the land use and river configuration that presently exist. It incorporates all the changes mentioned in Section 2. This model uses the 2008 bathymetry and topography developed specifically for this project. This run will serve as the baseline for comparison of the proposed project conditions for any effects on velocity and water surface elevation. The land use configuration for the existing conditions model is shown in Plate 1 in the appendix. Two flow conditions were modeled for existing conditions, bankfull flow and the 1957 design flow. 3.2 Project Conditions – Bank Armor, Bank Armor Removal and Riparian Restoration Hydraulic Model Runs The project conditions model runs incorporate bank armor to arrest the bank erosion and land uses associated with the previously developed “Site Specific Planting” plan developed in the Phase I study (MBK, 2004). Two flow conditions were modeled for these changes, bankfull flow and the 1957 Corps design flow. While a final design configuration has not been developed for the proposed bank armor, the model has incorporated a low level rock berm outboard of the existing bank vegetation that extends from the end of the existing armor to a point directly across the river from the irrigation pumping plant. It is anticipated that the berm will be planted with woody vegetation and additional stone materials will be added up the existing bank as needed to protect from the design flow velocities. The limit of additional armor is not known at this point, however it could be possible that armor will need to extent to the top of the existing eroding bank similar to the rock armor that exists at the upstream end of the project. Existing bank armor at RM 178.5 Right was also removed as this is part of the preferred alternative selected in the Ayres (2005) study. Removal of the bank armor is part of this proposed project and is intended to allow the upstream river meander to migrate freely and give the river the opportunity to cut off the bend. The bend cutoff is not a constructed or immediate project condition but an anticipated future condition that is the intended result of the bank armor removal. 4. HYDRAULIC MODELING

4.1 General This hydraulic model, refined from the previous Butte Basin 2D hydraulic Model, was also updated with all the changes mentioned in Section 2. It had been previously calibrated to the flood event that occurred on 10th and 11th of January 1995 (Ayres, 1997).


4.2 Model Development Geometric definition of the project reach is given in the form of a finite element network of triangular and quadrilateral elements as shown in Figure 3. The corner nodes of each element represent points in space (X,Y,Z) defining the topography of the project reach. These nodes were laid out using topographic mapping and aerial photography as a reference for element size and orientation. Nodes were also added at spot locations to define breaklines, structures, or other significant changes in topography. Elevation values were assigned to the nodes using a digital terrain model of the river reach. The original model reflects the river configuration as it existed after the 1995 flood events, based upon mapping developed for the USACE in August of 1995. In the river reach, material types within each element were categorized based on land use and roughness characteristics (dense vegetation, grassland, sandbars, etc.). Material types were assigned to each of the elements in the finite element mesh using aerial photography from the 1995 mapping effort conducted by the USACE and the 2002 Aerial Atlas. A field visit was also made to confirm land usage. For each material type, a Manning’s roughness coefficient (n value) was assigned to represent roughness. These values were determined primarily from the previous modeling effort, and originally were derived using standard engineering protocols and references. In the restoration area, roughness values were assigned based on tree planting density (high, medium and low) discussed and illustrated in Figures 13 and 14 of the Riparian Restoration Feasibility Study for the Riparing Sanctuary (River Partners 2005). After review of site conditions, the Manning’s n values for heavy riparian vegetation and orchards were reduced to 0.12 and 0.10 from 0.16 and 0.15 in the previous study to better represent site conditions, though values in these ranges are reasonable for these land use conditions. The low density vegetation attribute is assigned where rock armor is removed in the proposed condition. Material types and corresponding Manning’s n values used in the model are listed in Table 1.


Figure 3 - Example of the Finite Element Mesh near Project Area

Table 1 - Manning’s Roughness Coefficients (“n” Values)

Description of Model Land Use Material

Manning’s “n” Value

Main channel 0.035

Heavy riparian vegetation (High Density Vegetation) 0.120

Orchards 0.100

Cultivated field (fallow) 0.035

Bare sand bars 0.040

Managed wetlands 0.037

Pasture/Grassland 0.035

Structures 0.200

Sparse trees (Medium Density Vegetation 0.080

Savannah (Low Density Vegetation) 0.050

Stone bank protection 0.045


4.3 Boundary Conditions The input parameters required for the two-dimensional hydraulic model include defining inflows into the model and water surface elevations at the downstream limits. The bankfull flow was taken the Basis of Design Office Report for RM 177.8R (Ayres, 2008) and the design flow was taken from the 1957 Corps of Engineers design capacity for the flood control system. The hydraulic boundary conditions associated with these modeled flows are shown in Tables 2, 3, and 4. For the bankfull flow model the downstream water surface elevation was taken from the Basis of Design Office Report for RM 177.8R (Ayres, 2008). The downstream boundary conditions for the existing conditions design flow model were a water surface elevation and an outflow. Once this existing conditions model was solved, the water surface elevations at both of the downstream boundaries were used as the two downstream boundary conditions for the proposed conditions model.

Table 2 - Boundary Conditions for Bankfull Flow Model Run Boundary Condition Boundary Value

Sacramento River Inflow @ RM 181.5 90,455 cfs Main Channel Stage @ RM 176.0 100.16 ft

Table 3 - Boundary Conditions for Corps 1957 Design Flow Model Run - Existing Boundary Condition Boundary Value

Sacramento River Inflow @ RM 181.5 271,000 cfs Main Channel Stage @ RM 173 100.3 ft

Overbank Flow @ RM 173 111,000 cfs

Table 4 - Boundary Conditions for Corps 1957 Design Flow Model Run - Proposed Boundary Condition Boundary Value

Sacramento River Inflow @ RM 181.5 271,000 cfs Main Channel Stage @ RM 173 100.3 ft

Overbank Stage @ RM 173 104.1 ft

5. HYDRAULIC MODELING RESULTS 5.1 Existing Conditions – 2008 Land Use Hydraulic Model Runs The land use designations for the model mesh for the existing land condition are shown on Plate 1 in the Appendix. This run also includes the new geometry and associated roughness for the new bank protection at RM 177.8R installed by the Corps of Engineers in the fall of 2008.


Two hydraulic conditions were run for the existing, 2008 land use condition, one for the estimated bankfull condition and another for the Corps’ 1957 design flow. The primary purpose for running these two models was to develop an existing baseline for the comparison of velocity and water surface elevation changes for the proposed project. Plate 1 in the Appendix shows the model grid with the existing land use conditions overlaid. Plates 3 and 4 are velocity plots for the bankfull and design flow, respectively and Plate 5 is a plot of the water surface elevation for the design flow. 5.2 Project Conditions – Bank Armor, Bank Armor Removal and Riparian Restoration Hydraulic Model Runs The land use designations for the proposed project conditions are shown on Plate 2 and include stone bank armor along the eroding left bank and the “site specific” riparian planting plan in the overbank area on the east side of the channel. Plates 6 and 7 show the velocity plots for the bankfull flow and design flow model runs and Plates 8 shows water surface elevations for the design flow. Plates 9 and 10 are the differential comparison plots for velocity and water surface elevation for the design flow project conditions over existing design flow conditions. The highest flow velocities for all of the runs are in the main channel, just opposite and a bit upstream of the pumping plant. The velocities range from 7 to 9 fps across the channel with a maximum of 9.3 fps in the center of the channel. This location for the highest velocity is obviously the result of the narrowing of the channel as it comes around the bend and heads directly south past the pumping plant. The differential plot shows a modest increase of about 1 fps and mostly upstream of the pumping plant. Most of the changes in velocity occur along the left bank in the area where new armor is proposed. The final design of the armor will carefully look at these areas to insure there is adequate erosion protection in these areas. The differential water surface plots shows minor increase in water surface along the west levee (0.1 ft) and slightly larger increase in the overbank floodplain. A comparison of these water surface elevations in the main channel to those of the 1957 design water surface profile shows that the proposed project condition is still well below (2 to 3 feet) those elevations as can be seen in Figure 4, and will not affect the design flood control capacity of the system. Values for flow splits show that for the design condition there is approximately a 2,260 cfs, or 1%, increase in flow that goes into the Butte Basin Overflow and a corresponding reduction in the flow within the leveed section of the Sacramento River. The Phase I modeling for this project (Ayres 2005) also showed a small increase in flow into the Butte Basin and a minor decrease in flow into Butte Basin for the channel cutoff condition.


Figure 4. Water Surface Profile Comparisons

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175176177178179180181182183184185

River Mile (RM)

Ele

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VD

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Design Water Surface 2008 Land Use WSE Proposed Project WSE Right Levee Top

Figure 4 – Water Surface Profile Comparisons

6. CONCLUSIONS Based on the analyses performed and the stated results we offer the following conclusions:

1. The conclusions of the Ayres (2005) study remain valid and are consistent with this update. When combined, the project features have a neutral impact on the Sacramento River Flood Control Project. The potential channel cutoff would tend to convey more water into the downstream levee section. This is offset by the riparian floodplain habitat, which, due to the higher flow resistance, counteracts this tendency. All of the project features (riparian habitat, rock protection, rock removal and potential channel cutoff) serve to maintain a beneficial channel alignment at the irrigation diversion.

2. Bank armoring should be implemented across from the pumping plant to prevent river migration from progressing past this location. The anticipated upstream meander cutoff also promotes future beneficial alignment of the channel and the pumping plant intake.

3. The proposed project will not cause any loss in design capacity for the Sacramento River Flood Control System. The design water surface is not only much higher than what would be expected to actually occur in this area at the design discharge, but the changes that are expected due to this project are less than the level of uncertainty associated with the modeling.


4. There is approximately a 1% (2,260 cfs) increase in flow into the Butte Basin overflow area and a similar reduction within the leveed section of the Sacramento River. An even smaller decrease in flow into the Butte Basin overflow area could occur if the cutoff channel formed in the future.

5. Care should be taken in the design stage to carefully analyze the change in velocities in the main channel as it relates to erosion and deposition patterns. The rock armor should only protect the bank without significantly altering the existing bank geometry in order to maintain the flow patterns.

7. REFERENCES Ayres Associates, 1997. Hydrodynamic Modeling of the Sacramento River and Butte Basin from RM 174 to RM 194, Prepared for the US Army, Corps of Engineers, Sacramento District, December 1997. Ayres Associates, 2005. Two Dimensional Hydraulic Modeling, Llano Seco Riparian Sanctuary restoration and Potential Cutoff Channel, Sacramento River, RM 173 – 194, Prepared for MBK Engineers and River Partners, June 10, 2005. Ayres Associates, 2008. Bathymetric Survey and Mapping for pumping Plant Protection and Riparian Restoration at the Llano Seco Unit on the Sacramento River, Glenn and Butte County, California, October 8, 2008 Ayres Associates, 2008. Basis of Design Office Report, Sacramento River Bank Protection Project, Sacramento River erosion Control Sites at … …River Mile 177.8R…, Prepared for the US Army Corps of Engineers, Sacramento District, June 2008. MBK, 2004. Llano Seco Unit, Sacramento River Mile 178, Draft Pumping plant Protection Feasibility Study, Prepared for River Partners, December 2004. River Partners, 2005, Riparian Restoration Feasibility Study for the Riparian Sanctuary, November 30, 2005. River Partners, 2010. Pumping Plant Feasibility Study Final 05/08, email from Helen Swagerty, February 5, 2010.


PLATES

PLATE 1 – 2008 EXISTING LAND USE CONDITIONS PLATE 2 – PROPOSED PROJECT – BANK ARMOR AND SITE SPECIFIC PLANTINGS LAND USE CONDITIONS PLATE 3 – VELOCITY FOR BANK FULL FLOW – EXISTING CONDITIONS PLATE 4 – VELOCITY FOR DESIGN FLOW – EXISTING CONDITIONS PLATE 5 – WATER SURFACR ELEVATIONS FOR DESIGN FLOW – EXISTING CONSITIONS PLATE 6 – VELOCITY FOR BANK FULL FLOW – PROPOSED PROJECT PLATE 7 – VELOCITY FOR DESIGN FLOW – PROPOSED PROJECT PLATE 8 – WATER SURFACE ELEVATIONS FOR DESIGN FLOW – PROPOSED PROJECT PLATE 9 – VELOCITY DIFFERENTIAL FOR DESIGN FLOW PLATE 10 – WATER SURFACE DIFFERENTIAL FOR DESIGN FLOW

2150 River Plaza Dr Ste. 330

Sacramento, CA 95833

(916) 563-7700

ASSOCIATES ftp.ayresassociates.com

www.ayresassociates.com

Pumping PlantNear the Princeton Irrigation District

Sacramento River, RM 177-179Llano Seco Hydraulic Modeling

Plate 1. 2008 Existing Land Use Conditions

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Site Specific Plants - Land Use ConditionsPlate 2. Proposal Project - Bank Armor and

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CondtionsPlate 3. Velocity for Bank Full - Existing

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ConditionsPlate 4. Velocity for Design Flow - Existing

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Flow - Existing ConditionsPlate 5. Water Surface Elevation for Design

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CondtionsPlate 6. Velocity for Bank Full - Proposed

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ConditionsPlate 7. Velocity for Design Flow - Proposed

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Flow - Proposed ConditionsPlate 8. Water Surface Elevation for Design

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FlowPlate 9. Velocity Differential for Design

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2-DIMENSIONAL HYDRAULIC MODELING FOR … · INTRODUCTION ... System and to provide hydraulic parameters for the design of the bank armor. Two models were included in the project scope