# Presentation: 465240

## Bank-Stability and Toe-Erosion Model

**	**** **Andrew Simon, _Robert Thomas_, Andrea Curini and Natasha Bankhead
-  USDA-ARS National Sedimentation Laboratory, Oxford, MS
**	****	**

## Bank-Stability Model

**Version 5.0**

- 2-D wedge- and
-     cantilever-failures
- Tension cracks
- _Search routine for failures_
- Hydraulic toe erosion
- _Complex bank geometries_
- Positive and negative pore-water pressures
- Confining pressure from flow
- Incorporates layers of different strength
- _Vegetation effects: RipRoot_
- Inputs: s, *c*’, ’, b , *h*, *u*w,
-     *k*, c

- Confining pressure

- Tensiometers
- (pore pressure)

- shear surface

- WATER LEVEL, M

## Web Address

## Model Structure

-  **Introduction page**: provides general background
-  **Technical Background page**: provides equations for stability analysis including positive and negative pore-water pressures, effects of vegetation, and the toe-erosion algorithm.
-  **Model Use and FAQ page**: provides methodology for application of model features including hints for working with bank geometry, selecting the shear surface, soil layers, pore-water pressure/water table, vegetation, and the toe-erosion algorithm.

## Model Structure (cont’d)

**Input Geometry page**: Enter coordinates for bank profile, soil layer thickness, and flow parameters..
**Bank Material page**: Enter bank-material properties (geotechnical and hydraulic)
**Bank Vegetation and Protection** page: Run root reinforcement (RipRoot) model and to input  default values of bank and toe protection.
**Bank Model Output page**: Enter water-table depth and obtain results.

## Model Structure (cont’d)

**Toe Model Output page**: Run shear stress macro and obtain toe-erosion results.
**Unit Converter page**: Imperial (English) to metric units

## Modeling Steps

- Model the current bank profile by first evaluating the effect of hydraulic erosion at the bank toe.
- Take the resulting new profile and run this in the bank- stability model to see if the eroded bank is stable.
- Investigate the effects of water-table elevation, stage, tension cracks, vegetation, and toe protection.

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**

## Introduction Sheet

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**

## Input Geometry Sheet

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**
**Select EITHER Option *****A***** or Option *****B *****for***** *****bank geometry and input geometry data. For this first example select Option *****B*****.**

## Input Geometry Sheet

## Starting with Option B

- If you don’t know failure-plane angle, search routine will solve for it.

**Select: Option B**
** ****5m high bank**
** ****85 degree angle**
** ****1m toe length**
** ****25 degree toe angle**

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**
**Select EITHER Option *****A***** or Option *****B *****to input bank geometry**
**Enter Bank-layer Thickness**

## Enter Bank Layer Thickness

## Enter Bank Layer Thickness: Detail

**For this example, enter 1m thicknesses for all five layers**

- Layer 5 should (but does not have to) end at or below the base of the bank toe. Therefore, the basal elevation of layer 5 should be equal to or less than the elevation of point V (base of bank toe) if Option A is selected or 0 (zero) if Option B is selected.

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**
**Select EITHER Option *****A***** or Option *****B *****to input bank geometry**
**Enter bank-layer thickness**
**Enter channel and flow parameters, and check cross section inputs:**
**	****	****a. View Geometry**
**	****	****b. Bank Geometry Macro**

## Channel and Flow Parameters

## Channel and Flow Parameters: Detail

**Input the above values for this example**

## Check Cross Section Inputs I: (View Geometry)

## View of Input Cross Section

## Check Cross Section Inputs: II (Geometry Macro)

## Check Geometry and Flow Level 

- Model will direct you to the Bank Material sheet
- Click on Bank Model Output sheet

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**
**Select EITHER Option *****A***** or Option *****B *****to input bank geometry**
**Enter Bank-layer Thickness**
**Enter channel and flow parameters**
**Enter Bank-material Properties: Click on “Bank Material” sheet**

## Select Bank Materials by Layer

**Select bank materials by layer from drop down boxes. For this case:**
**Layer 1** = Moderate soft clay,
**Layer 2** = Moderate soft clay,
**Layer 3** = Moderate silt,
**Layer 4** = Erodible silt,
**Layer 5** = Moderate silt,
**Bank Toe Material** = Own data

## Selecting Bank Materials

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**
**Select EITHER Option *****A***** or Option *****B *****to input bank geometry**
**Enter Bank-layer Thickness**
**Enter channel and flow parameters**
**Enter Bank-material Properties: Click on “Bank Material” sheet **
**Select “Toe Model Output” sheet and Click on “Run Toe-Erosion Model”**

## Toe Model Output Sheet

## Results of Toe-Erosion Model

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**
**Select EITHER Option *****A***** or Option *****B *****to input bank geometry**
**Enter Bank-layer Thickness**
**Enter channel and flow parameters**
**Enter Bank-material Properties: Click on “Bank Material” sheet **
**Select “Toe Model Output” sheet and Click on “Run Toe-Erosion Model”**
**Export Coordinates to Model (Returned to “Input Geometry” sheet)**

## Profile Exported into Option A(Model Directs you to “Input Geometry” sheet)

**Either: (1) Select shear emergence elevation and shear angle or (2) leave blank for search routine**

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**
**Select EITHER Option *****A***** or Option *****B *****to input bank geometry**
**Enter Bank-layer Thickness**
**Enter channel and flow parameters**
**Enter Bank-material Properties: Click on “Bank Material” sheet **
**Select “Toe Model Output” sheet and Click on “Run Toe-Erosion Model”**
**Export Coordinates to Model (Returned to “Input Geometry” sheet)**
**Run “Bank Geometry Macro” and Click on “Bank Model Output” sheet; Set water-table depth and Click “Run Bank Stability Model”**

## Data for Pore-Water Pressure

**Data for Pore-Water Pressure**

**Or**

**In “Bank Model Output” worksheet**

- In this case select option to use water table depth, and enter a value of 3.0m below the bank top

## Bank Model Output: No Tension Crack

**Bank Model Output: No Tension Crack**

## Bank Model Output: Specific Results

**Failure plane from search routine**

**Failure dimensions (loading)**

**Save your file under a different name**

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**
**Select EITHER Option *****A***** or Option *****B *****to input bank geometry**
**Enter Bank-layer Thickness**
**Enter channel and flow parameters**
**Enter Bank-material Properties: Click on “Bank Material” sheet **
**Select “Toe Model Output” sheet and Click on “Run Toe-Erosion Model”**
**Export Coordinates to Model (Returned to “Input Geometry” sheet)**
**Run “Bank Geometry Macro” and Click on “Bank Model Output” sheet; Set water-table depth and Click “Run Bank Stability Model”**
**Save file under different name**

## How can you make this bank more stable or more unstable?

- Try experimenting with the following parameters to get a feel for the model:
- Water surface elevation (Input Geometry Sheet)
- Shear angle (Input Geometry Sheet)
- Water table height (Bank Model Output sheet)
- Bank material types (Bank Model Output sheet)

**We’ll work with the effects of vegetation later...**

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**
**Select EITHER Option *****A***** or Option *****B *****to input bank geometry**
**Enter Bank-layer Thickness**
**Enter channel and flow parameters**
**Enter Bank-material Properties: Click on “Bank Material” sheet **
**Select “Toe Model Output” sheet and Click on “Run Toe-Erosion Model”**
**Export Coordinates to Model (Returned to “Input Geometry” sheet)**
**Run “Bank Geometry Macro” and Click on “Bank Model Output” sheet; Set water-table depth and Click “Run Bank Stability Model”**
**Save file under different name**
**Open file and Click on “Bank Vegetation and Protection” sheet**

## Incorporating Vegetation Effects and other Protection

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**
**Select EITHER Option *****A***** or Option *****B *****to input bank geometry**
**Enter Bank-layer Thickness**
**Enter channel and flow parameters**
**Enter Bank-material Properties: Click on “Bank Material” sheet **
**Select “Toe Model Output” sheet and Click on “Run Toe-Erosion Model”**
**Export Coordinates to Model (Returned to “Input Geometry” sheet)**
**Run “Bank Geometry Macro” and Click on “Bank Model Output” sheet; Set water-table depth and Click “Run Bank Stability Model”**
**Save file under different name**
**Open file and Click on “Bank Vegetation and Protection” sheet**
**Click “Run Root-Reinforcement Model”**

## Root Reinforcement using RipRoot

## Root Reinforcement using RipRoot

**Root Reinforcement using RipRoot**

_**Simple Case: 1 species**_

## RipRoot: Results

## Operational Steps

**Open Excel file “BSTEM-5.0”**
**Click on “Enable Macros”...to “Introduction” sheet**
**Click on “Input Geometry” sheet**
**Select EITHER Option *****A***** or Option *****B *****to input bank geometry**
**Enter Bank-layer Thickness**
**Enter channel and flow parameters**
**Enter Bank-material Properties: Click on “Bank Material” sheet **
**Select “Toe Model Output” sheet and Click on “Run Toe-Erosion Model”**
**Export Coordinates to Model (Returned to “Input Geometry” sheet)**
**Run “Bank Geometry Macro” and Click on “Bank Model Output” sheet; Set water-table depth and Click “Run Bank Stability Model”**
**Save file under different name**
**Open file and Click on “Bank Vegetation and Protection” sheet**
**Click “Run Root-Reinforcement Model”**
**Return to “Bank Model Output” sheet**

## Still Unstable with Vegetation

**Still Unstable with Vegetation**

**Revised strength and *****F******s****** *****calculated automatically**

## Conditionally Stable with Lower Water Table

**Conditionally Stable with Lower Water Table**

**Revised pore-water pressures and *****F******s****** *****calculated automatically**

**Change water-table depth to 3.5 m**

## Further Simulations...Tension Cracks

**We often use 1⁄2 the value or observed vertical-face heights**

## Results with Tension Crack

***F******s****** *****= 0.79**
**Bank is unstable again due to loss of strength along upper part of failure plane.**

## Bank-Toe Protection

**Re-open BSTEM-5.0.xls**
**Select “Input Geometry sheet”**
**Select Option B**
**Input these values:**
**Input channel and flow parameters**
**Click “Run Bank Geometry Macro”**
**Open “Bank Material” sheet**
**Select “Moderate silt” for all layers**
**Select “Toe Model Output” sheet**
**Click “Run Toe-Erosion Model”**

## Toe Erosion without Protection

**Toe Erosion = 0.62 m****2**

## Bank-Toe Protection

**Re-open BSTEM-5.0.xls**
**Select “Input Geometry sheet”**
**Select Option B**
**Input these values:**
**Input channel and flow parameters**
**Click “Run Bank Geometry Macro”**
**Open “Bank Material” sheet**
**Select “Moderate silt” for all layers**
**Select “Toe Model Output” sheet**
**Click “Run Toe-Erosion Model” and notate results**
**Select “Bank Material” sheet and select **_**boulders**_** for layer 5 and toe material**
**Select “Toe Model Output” sheet and click “Run Toe-Erosion Model”**

## Toe Erosion with Protection

**Toe Erosion = 0.15 m****2**

## Distinguish Between Hydraulic and Geotechnical Bank Protection

- Toe armoringrock, LWD, live vegetation, fiberschines
- Bank face armoringmattresses, vertical bundles, geotextiles
- Bank reinforcementpole and post plantings, bank top vegetation, brush layers, drainage

## Distinguish Between Hydraulic and Geotechnical Bank Protection

- Hydraulic protection reduces the available boundary hydraulic shear stress and increases the shear resistance to particle detachment

- Geotechnical protection increases soil shear strength and decreases driving forces