high flow sediment bypass for robles diversion dam presentation

High Flow Sediment Bypass for Robles Diversion DamBrent Mefford, Blair Greimann, and Yong LaiTechnical Service CenterDenver, ColoradoMay 2008

Aerial Views

Aerial view of Robles Diversion Dam, 2005 Aerial view with AutoCAD model overlay

• Crest Elevation: 767 ft• Structural Height: 24 ft• Hydraulic Height: 13 ft• Crest Length: 530 ft• Volume: 11,000 yd3

Background

• Sluice Radial Gate Structure– 4 Radial gates (1-10’x9.5’, 3-16’x9.5’)

• Discharge Capacity: 6,000 cfs– Associated features:

» Spillway & Baffle Section

Existing Conditions

• Diversion Canal– 3 Radial gates (11’ x 10.5’)

• Discharge Capacity: 500 cfs

Downstream of Sluice Radial Gate Structure

Sluice Radial Gate Structure (Left)and Diversion Canal (Right)

Existing Conditions• Downstream

– Boulders & Cobbles– Vegetation

Downstream of Sluice Radial Gate Structure (Left)

Upstream

Downstream

Existing Conditions

Sedimentation at Fish Entrance

2005 Flood (less than 10-yr flood)

Existing Conditions

Entrance Conditions at Gates

2005 Flood (less than 10-yr flood)

overtopping and damage to dam

2005 Flood (less than 10-yr flood)

Existing Conditions

Existing Conditions

Debris Loads at Fish Screens

2005 Flood (less than 10-yr flood)

• Determine flow capacity and the best location for the spillway structure (left bank or right bank) based on sediment sluicing performance and impacts on upstream fish passage.

• Identify potential modifications to the design that would enhance sediment sluicing, fish passage and minimize the potential for fish stranding.

• Identify spillway operational patterns that promote sediment sluicing fish passage and prevention of fish stranding.

Objectives

• Physical Model: – Tested with and without HFSB– Tested Medium flow (6,000 cfs) and higher flow (14,000

cfs)• Numerical Modeling:

– compared against laboratory experiements– Simulated without and without Matilija Dam Removal– Simulated without and without HFSB

• Fish Passage:– Designed and tested single pool with fish ladder

Tasks

• Bed load at Robles Diversion will increase after Matilija Dam Removal, potentially entering canal and reducing diversions

• HFSB improves the sediment sluicing and will reduce the bedload entering Robles Canal

• Existing debris loads and suspended sediment loads will remain high

• Existing fishway entrance will need to be raised due to sedimentation

• Additional fish ladder will minimize fish stranding at HFSB

• Raise of dam crest provides greater operational flexibility for diversion and fish ladder

Summary of Results

Final Design Recommendations

Design Recommendations

Downstream of Diversion

Existing spillway

HFSB

Downstream of Diversion

Fishwayexit

Downstream of Diversion

HFSB Spillway

Fishwayentrance

• Test Conditions– Existing Conditions

• Assuming Matilija Dam Removed– Sluice Radial Gate Structure– Diversion Canal Structure

– Proposed Conditions• High Flow Sediment Bypass (HFSB)

Radial Gate Structure

– 4 Radial gates (10’ x 30’)– Discharge Capacity: 11,000 cfs

• Sluice Radial Gate Structure• Diversion Canal Structure

Physical Model

Sluice Radial Gate Structure (Left)and Diversion Canal (Right)

High Flow Bypass Radial Gate Structure

Physical Model

Physical Model

• Test Flows– 6,000 cfs

• 1991 Flood

– 14,000 cfs • 1998 Flood

Physical Model Tests

• Water Surface Elevations– Point Gages

• Dam Crest• Upstream Fishway Exit• Upstream of Spillway Weir

• Velocity– Recorded during peak flow– Measured 1’ (20’ prototype) from upstream toe of dam

• 8 stations– 2.5’ centers

– Deposition• Photogrammetry

– Estimate sediment volume– Survey

• Sediment elev. along downstream perimeter of depositions– Soil samples

• Gradation analysis to compare with original sediment bed composition

Data Collection

Current Condition Test Results

• Existing Conditions – Sluice Radial Gate Structure & Diversion Canal

• Sediment passes through both structures• Sediment deposits in spillway and diversion canal

Results – 6,000 cfs

• Existing Conditions – Sluice Radial Gate Structure & Diversion Canal

Results – 6,000 cfs

Upstream of Sluice Radial Gate Structure

Spillway Downstream of Sluice Radial Gate Structure

Upstream of Diversion Canal

Upstream Fishway Exit

• Sediment Quantities– 3.14 yd3 placed in model– 0.049 yd3 accumulated upstream of spillway weir 1– 0.011 yd3 accumulated within diversion canal

Results – 6,000 cfs• Existing Conditions

– Sluice Radial Gate Structure & Diversion Canal

• Existing Conditions – Sluice Radial Gate Structure & Diversion Canal

• Sediment passing through both structures• Sediment fills spillway & diversion canal• Sediment reaches crest of dam

Results – 14,000 cfs

• Existing Conditions – Sluice Radial Gate Structure & Diversion Canal

Results – 14,000 cfs

Upstream of Sluice Radial Gate Structure & Dam Crest

Spillway Downstream of Sluice Radial Gate Structure

Downstream of Diversion Canal

Upstream Fishway Exit

• Sediment Quantities– 5.63 yd3 placed in model– 0.281 yd3 accumulated upstream of spillway weir 1– 0.131 yd3 accumulated within diversion canal

Results – 14,000 cfs• Existing Conditions

– Sluice Radial Gate Structure & Diversion Canal

Proposed Condition Test Results

• Proposed Conditions – Sluice Radial Gate Structure & Diversion Canal – High Flow Bypass Radial Gate Structure (At Right Bank)

• Sediment passing through both structures• Sediment fills spillway, Diversion Canal clear

Results – 6,000 cfs

High Flow Bypass Structure Sluice Radial Gate Structure

Diversion Canal

Results – 6,000 cfs

Upstream of Sluice Radial Gate Structure& Diversion Canal

Baffle Section Downstream of Sluice Radial Gate Structure

Upstream Fishway Exit

• Proposed Conditions – Sluice Radial Gate Structure & Diversion Canal – High Flow Bypass Radial Gate Structure (At Right Bank)

Upstream of HFSB Radial Gate Structure

• Proposed Conditions – Test Velocities

Results – 6,000 cfs

Image at 2.40 cfs (4,293 cfs)

15-18 ft3/s

• Sediment Quantities– 4.58 yd3 placed in model– 0.000 yd3 accumulated upstream of spillway weir 1– 0.000 yd3 accumulated within diversion canal

Results – 6,000 cfs• Proposed Conditions (Right Bank)

• Proposed Conditions – Sluice Radial Gate Structure & Diversion Canal – High Flow Bypass Radial Gate Structure (At Right Bank)

• Sediment passing through both structures• Sediment fills spillway, Diversion Canal clear

Results – 14,000 cfs

High Flow Bypass Structure

Sluice Radial Gate Structure

Diversion Canal

Results – 14,000 cfs

Upstream of Sluice Radial Gate Structure& Diversion Canal

Spillway Downstream of Sluice Radial Gate Structure

Upstream Fishway Exit

• Proposed Conditions – Sluice Radial Gate Structure & Diversion Canal – High Flow Bypass Radial Gate Structure (At Right Bank)

Upstream of HFSB Radial Gate Structure

• Proposed Conditions (Right Bank)– Test Velocities

Results – 14,000 cfs

Image at 7.90 cfs (14,132 cfs)

15-18 ft3/s

• Sediment Quantities– 5.85 yd3 placed in model– 0.383 yd3 accumulated upstream of spillway weir 1– 0.000 yd3 accumulated within diversion canal

Results – 14,000 cfs• Proposed Conditions (Right Bank)

• Sluice Gate Radial Structure Spillway – Filled during high flows

• Diversion Canal Structure– Clear during high flows with

HFSB Structure in place

• Fish Bypass Structure– Plugged during high flows

at both entrance and exit

• Gate Operations– Aids in directing sediment

transport

Physical Model Study Conclusions

Numerical Model Results: Without HFSB

(b) After Matilija Dam removal(a) before Matilija Dam removal

Numerical Model Results: after Matilija Dam Removal

(b) With HFSB(a) Without HFSB