NCED Stream Restoration Toolbox

The Dam Remover: MARK1

By: Alessandro Cantelli

February 2006 – Version 1.0

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The Stream Restoration Toolbox

The Stream Restoration Toolbox consists of current basic research cast into the form of tools that can be used by practitioners. The details of a tool are presented through a PowerPoint presentation, augmented by embedded Excel spreadsheets or other commonly available applications. The toolbox is a vehicle for bringing research findings into practice.

While many tools are being developed by NCED Researchers, the opportunity to contribute a tool to the Toolbox is open to the community. For more information on how to contribute please contact Jeff Marr at marrx003@umn.edu.

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Statement of liability and usage

This tool is provided free of charge. Use this tool at your own risk. In offering this tool, the following entities and persons do not accept any responsibility or liability for the tool’s use by third parties:

• The National Center for Earth-surface Dynamics;

• The universities and institutions associated with the National Center for Earth-surface dynamics; and

•The authors of this tool.

Users of this tool assume all responsibility for the tool results and application thereof. The readers of the information provided by the Web site assume all risks from using the information provided herein. None of the above-mentioned entities and persons assume liability or responsibility for damage or injury to persons or property arising from any use of the tool, information, ideas or instruction contained in the information provided to you.

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Title Page Title Page

Tool Title: The Dam Remover: Mark 1Tool Author: Alessandro Cantelli, PhD.Author e-mail: Alessandro.Cantelli@shell.comVersion: 1.0Associated files:

1) DamRemoverMARK1.ppt2) DamRemoverMARK1.xls

Date: February 2006

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• Warnings on tool limitations• Introduction to the Tool

• Some important reasons to remove dams• Morphodynamics of rivers ending in 2D/1D deltas• Tool Focus: reservoirs with diminished water capacity

• Tool Overview• Narrowing versus Widening• Experiments – Data

•Experiments: general observations• Introduction to DamRemovalMARK1.xls

•The conceptual model• The model and the approximations• Initial and boundary conditions

• DamRemovalMARK1.xls• Using the tool: three examples• Work in process• References

Outline of this Document

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The present tool is related to the specific case of the morphodynamic evolution of a deltaic deposit due to dam removal. This tool does not consider other important and crucial factors. In order to make a decision on the removal of a specific dam it is strongly recommended that consideration be given to these other perspectives.

In particular the following aspects need to be considered: • GEOCHEMESTRY ( i.e. presence of pollutants stored in the reservoir)• BIOLOGY and ECOLOGY ( i.e. impact of the procedure on the ecosystem)• SOCIOLOGY (i.e. impact of the procedure on nearby communities)• ECONOMY (i.e. impact of the procedure on the economy of the area)• …….. And others.

Warnings on tool limitations

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Removing a dam is the most drastic of available options for dam remediation. The most commonly cited benefits of removal include:• improvement in upstream fish passage• restoration of the natural transport of river sediment • reinstatement of natural peak flows and seasonal flooding.

The negative consequences of removal are:• associated massive release of sediment• temporary destruction of desirable habitats that have developed after dam installation

Alternatives to complete removal of a dam are: Dam breaching, dam modification, modification of water-use practices, sluicing to remove accumulated sediment.

This tool is directed to the erosion associated with dam removal.

Introduction to the tool

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Some important reasons to remove dams•Many structures are approaching their design life, and therefore may

be unsafe;

• Environmental damage is often caused by the dam (e.g. fish habitat);

•Rivers returned to their natural state may have positive economic and

social benefits.

•Reservoirs behind dams are filling with sediment and losing their

effectiveness;

This tool is related to this issue.

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Reservoirs behind dams are filling with sediment and losing their effectiveness

View of the delta of the Eau Claire River as it enters Lake Altoona, a reservoir in

Wisconsin, USA

1951 1988

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Morphodynamics of rivers ending in 2D/1D deltas

When rivers flow into bodies of standing water such as lakes or reservoirs, they typically form fan-deltas that spread out laterally as they prograde in the streamwise direction.

If the river is confined by a narrow canyon, however, the installation of a dam can lead to a nearly 1D delta that progrades downstream. An example is shown on the next page.

Fan-delta at the upstream end of Mills Lake, a reservoir on the Elwha River, Washington, USA.(Image courtesy Y. Cui.)

From Gary Parker’s e-book http://cee.uiuc.edu/people/parkerg/

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AN EXAMPLE OF A 1D DELTA

Hoover Dam was closed in 1936. Backwater from the dam created Lake Mead. Initially backwater extended well into the Grand Canyon. For much of the history of Lake Mead, the delta at the upstream end has been so confined by the canyon that it has propagated downstream as a 1D delta. As is seen in the image, the delta is now spreading laterally into Lake Mead, forming a 2D fan-delta.

View of the Colorado River at the upstream end of Lake Mead.

Image from NASAhttps://zulu.ssc.nasa.gov/mrsid/mrsid.pl From Gary Parker’s e-book http://cee.uiuc.edu/people/parkerg/

12Courtesy http://pages.sbcglobal.net/pjenkin/matilija/

Tool Focus: Reservoirs with diminished water capacity

The Dam Remover: Mark 1 tool is designed to simulate removal of a dam where the reservoir sediments are close to the dam itself and water storage capacity has been dramatically reduced by sedimentation. The tool models the morphodynamics of the channel that incises into the delta after dam removal.

Upstream face of Matilija dam, sediments are adjacent to the structure

Matilija dam during flood event

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This tool consists of a simplified 1D model implementing the time evolution of a channel incising into a deltaic deposit. In particular, the tool considers the evolution of the longitudinal profile and the width of the incising channel.

The model is designed to track the evolution of bed elevation and bottom width of a channel incising into the topset of a deltaic deposit when subjected to a degradational setting due to the removal of the dam.

The tool can be used to help estimate the morphodynamic evolution of the deltaic deposit due to dam removal.

The Tool does not, however, cover a limitless range of cases; it has specific limitations that need to be considered. Some of these limitations are discussed below.

Tool Overview

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Experiments carried out in a flume at St. Anthony Falls Laboratory, University of Minnesota have been focused on sedimentation and erosion processes in reservoirs characterized by well sorted and non-cohesive sediments. Results have shown an interesting phenomenon that we refer to as “erosional narrowing”. This occurs immediately after the sudden removal of a dam that is filled with sediment. A channel incises into the deposit after failure of the leading front of the sediment deposit. In the early stages of incision this channel may become significantly narrower as it undergoes rapid degradation. Both incision and narrowing propagate upstream over a relatively short time. In the long term however, the depositional contribution from the side slopes eventually balances and then surpasses erosional narrowing, so the channel widens toward some new equilibrium state with a lower streamwise slope. This picture is at variance with the general belief that the incisional channel widens from the very beginning. “Erosional narrowing” does not occur under all conditions, but in many cases it is an important factor in the evolution of channel width and bed elevation.

Narrowing versus widening

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On the left: sketch of the facility.

On the right: photo of the flume used.

View from downstream Overhead View

Flow

FRONT

Experiments - Data

front_view.mpg and plan_view.mpg : to run without relinking, download to same folder as this PowerPoint presentation.

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20

25

30

35

40

45

200 300 400 500 600 700 800 900 1000 1100

Distance in the downstream direction (cm)

Bed

ele

vatio

n (c

m)

0 23 120 410 840

1800 4200 6000

The original location of the dam removed wasat 900 cm in the downstream direction

'Pivot' point

Time (s) after dam removal

Time evolution of the channel long profile after dam removalTime evolution of the channel long profile after dam removalThe observed time evolution of the longitudinal profile is shown in this plot. For the The observed time evolution of the longitudinal profile is shown in this plot. For the non-cohesive non-cohesive materialmaterial tested in these experiments, an important observation is made: the erosional and tested in these experiments, an important observation is made: the erosional and depositional zones rotate in time around a point located approximately at the centerpoint of the depositional zones rotate in time around a point located approximately at the centerpoint of the delta front. This result provides one of the boundary conditions used in the tool.delta front. This result provides one of the boundary conditions used in the tool.

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0

5

10

15

20

25

30

0 30 60 90 120 150 180 210 240 270 300

Time (s)

Cha

nnel

wid

th (

cm)

847.5 845 842.5 840 835 830

825 820 810 780 740

Location (cm) downstream of flume entrance

slow wideningslow widening

rapid narrowing

rapid narrowing

Time evolution of the width of the channel water surface at various points Time evolution of the width of the channel water surface at various points upstream of the dam after removalupstream of the dam after removalEach line corresponds to a different transverse section (i.e., to a different distance upstream of Each line corresponds to a different transverse section (i.e., to a different distance upstream of the sediment feed point.) Distances are in centimeters. The dam is located 900 cm downstream the sediment feed point.) Distances are in centimeters. The dam is located 900 cm downstream of the inlet section.of the inlet section.

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• In a dam/reservoir system that is filled with sediment (i.e. when the sediment front is adjacent to the dam), sudden removal of the dam results in 1) “rapid” base-level lowering and 2) a “sufficiently” upward convex long profile.

• Both incision and narrowing propagate upstream.

• The time scale of the narrowing process is very short. Streamwise bed slope declines as the channel narrows.

• The greatest erosion is at the center of channel, where it overcomes the depositional contribution from the side slopes.

• In the long-term, the channel eventually stops narrowing and starts to widen. The banks continue to erode, and the streamwise bed slope continues to decline in time.

Experiments: General Observations

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• The Dam Remover Tool is a tool in the NCED Stream Restoration Toolbox. The slides that follow give an overview of the conceptual model for the tool, initial and boundary conditions, governing equations, assumptions and an overview of model use.

• The tool is designed to study the effects of the removal of the dam on a pre-existing deltaic deposit in the reservoir. The tool is written in MSExcel (Visual Basic for Applications embedded in an Excel spreadsheet) and is designed to be relatively easy to use.

• The scenarios that can be considered include both “blow and go,” i.e. the sudden removal of a dam and staged removal.

Introduction to DamRemovalMARK1.xls

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The above diagram provides a schematic view of the process of incision observed in the experiments, in terms of the trajectories of the left and right side of the channel bottom. Immediately after dam removal, incision is rapid and the channel narrows; while the sidewalls erode, narrowing suppresses this erosion. Eventually, rapid incision with channel narrowing gives way to slow incision with channel widening; the widening enhances sidewall erosion.

The Conceptual Model

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The Dam Remover Tool considers general and simplified conditions, and is designed to give an approximation of the impact on the reservoir due to the sudden removal of a dam.

CHANNEL HYDRAULICS AND ANALYSIS OF THE SIMPLIFICATIONS USED

Channel Geometry• Single channel• Straight channel• Trapezoidal cross section• Specified initial widthFlow Hydraulics• Flow conditions approximated as normal (uniform and steady)• The Manning-Strickler flow resistance relationship is used.• The shear stress bb on the bed region of the active channel is related to the shear stress bs on the side region of the active channel by a constant value .

bbbs

The Model and the Approximations

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Sediment Transport• The sediment is non-cohesive.• The sediment is approximated by a single grain size.• The streamwise volume bedload transport rate per unit width on the bed and

the sidewall regions (qbsb and qbss, respectively) are estimated using Parker’s

approximation of the Einstein (1950) bedload transport relation (Parker, 1979).• Transverse (normal) bedload transport is estimated using the formulation of

Parker and Andrews (1985) under the added assumption of negligible

secondary flow.

The Model and the Approximations

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The definitions used in the Figure are: x = streamwise coordinate (directed out of the page)y = transverse coordinate (origin at the center of the channel and positive toward the right bank)z = vertical coordinateSs = side slope of the channel banks (constant value)H = water depth of the bed region (defining the active channel)Bb = half the channel bed widthBw = half the channel top widthBs = width of one sidewall region (including both submerged and emergent banks)b = bed elevation on the bed regiont = elevation of the top of the active channele = elevation of the top of the channel bankL = bank arc length normal to flow direction.

Conceptual model for erosional narrowingCross-section at time t: solid line cross-section at time t+t: dashed line.

The Model and the Approximations

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qbs denotes the total volume bedload transport rate per unit width in the streamwise direction

qbn denotes the corresponding bedload transport rate per unit width in the transverse (normal) flow direction

qbsb is the streamwise volume bedload transport rate per unit width on the bed region

qbss is the streamwise volume bedload transport rate per unit width on the sidewall region, which is assumed to be the same on either bank

qbnb is the transverse (normal) volume bedload transport rate per unit width on the bed region

qbns is the transverse (normal) volume bedload transport rate per unit width on the sidewall region, which is assumed to be the same on either bank

Conceptual model for erosional narrowingCross-section at time t: solid line cross-section at time t+t: dashed line.

The Model and the Approximations

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Initial conditions:• Specified longitudinal profile of the deltaic deposit (given as ABC in Figure)• Initial channel width along the topset of the delta (given as AB in Figure)

Boundary conditions• Downstream boundary condition is represented by a fixed PIVOT POINT as observed in the experimental data. This point is located proximally at the half height Hd of the delta front as shown in the Figure.

Hd

2 Hd

AB

C

DABD = Deltaic depositABC = Part of the deltaic deposit treated in the model

Flow

Initial and Boundary Conditions

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IMPORTANT: In the case of “staged removal” the point C is represented by the crest of the dam.

Hs

Hd

AB

D

C

C

ABD = Deltaic depositABC = Part of the deltaic deposit treated in the model

Flow

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• The upstream boundary condition is represented by a specified constant total bedload transport rate at upstream end. More specifically, the model computes the equilibrium sediment transport rate associated with the initial cross-sectional geometry and bed slope of the cross-section farthest upstream.

Sketch of the initial trapezoidalchannel above the deltaic deposit

Initial Longitudinal bed profile

Initial Channel Width

Pivot axis

A

B

C

C

B

A

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These parameters need to be input before starting the calculation. The parameters are discussed in the Appendix

Using the Excel workbook DamRemovalMARK1.xls

Worksheet “Auxiliary Parameters”

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The worksheet Initial Topography sheet is used to input the geometry of the delta,in terms of the slope of the topset of the delta, the slope of the front and the streamwise and vertical coordinates of the intersections with the preexisting slope before delta formation. All are required parameters.

Enter the Spatial step. The total number of stepsIs automatically calculated.

Worksheet “Initial Topography”

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Scroll down in the “Initial Topography” work sheet. The initial longitudinal profile is calculated by clicking on the indicated button.

Worksheet “Initial Topography” (continued)

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The equilibrium channel widths associated with the delta slope, pre-delta slope, and front slope are calculated. The program requires an initial channel width, and also a maximum channel width that represents a limitation often defined by the valley width at the reservoir elevation.

Worksheet “Initial Topography” (continued)

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Insert ParametersHere the total number of time steps and the time step duration in seconds is required.The light blue cells give the time duration in seconds and minutes

Click on the gray button to perform the calculation after making sure that all the parameters in the worksheets “Initial Topography” and “Auxiliary Parameters” are also input properly. A countdown of time steps in the green cell measures the progress of the calculation.

Worksheet “Calculator”

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Results: worksheets “Bed Elevation” and “Bed Elevation plot”

Bed elevation results are presented and plotted for the times specified in worksheet “Calculator”. The plot is set up to accommodate up to 20 profiles. If more are specified the user must add these manually to the plot.The profile at each time is located in a different column as illustrated.

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The width evolution along the channel is presented and plotted for the different times requested in the Calculator Worksheet. The plot is set up to accommodate up to 20 profiles. If more are specified the user must add these manually to the plot. The profile at each time is located in a different column as illustrated.

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Erosion of a channel into three different deltaic deposits are analyzed In the following slides.

The main difference between the deltas is one of scale.

1. Laboratory scale with a characteristic stramwise length of about 10 m and a height of about 30 cm.

2. Small dam scale with a characteristic streamwise length of about 100 m and a height of about 3 m.

3. Medium size dam scale with a characteristic streamwise length of about 1 km and a height of about 30 m.

Using the tool: Three examples

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1. Laboratory scale with a characteristic streamwise length of about 10 m and a height of about 30 cm

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1. Laboratory scale with a characteristic streamwise length of about 10 m and a height of about 30 cm (contd.)

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1. Laboratory scale with a characteristic streamwise length of about 10 m and a height of about 30 cm (contd.)

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1. Laboratory scale: results for long profile

Legend in seconds

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1. Laboratory scale: results for channel width

Legend in seconds

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1. Laboratory scale: results for water depth

Legend in seconds

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1. Laboratory scale: results for volume sediment transport rate/unit width

Legend in seconds

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2. Small dam scale with a characteristic length of about 100 m and a height of about 3 m

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2. Small dam scale with a characteristic length of about 100 m and a height of about 3 m (contd.)

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2. Small dam scale with a characteristic length of about 100 m and a height of about 3 m (contd.)

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2. Small dam scale: results for long profile

Legend in seconds

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2. Small dam scale: results for channel width

Legend in seconds

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2. Small dam scale: results for water depth

Legend in seconds

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2. Small dam scale: results for volume sediment transport rate/ unit width

Legend in seconds

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3. Medium size dam scale with a characteristic length of about 1 km and a height of about 30 m

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3. Medium size dam scale with a characteristic length of about 1 km and a height of about 30 m (contd.)

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3. Medium size dam scale with a characteristic length of about 1 km and a height of about 30 m (contd.)

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3. Medium size dam scale: results for long profile

Legend in seconds

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3. Medium size dam scale: results for channel width

Legend in seconds

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3. Medium size dam scale: results for water depth

Legend in seconds

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3. Medium size dam scale: results for volume sediment transport/unit width

Legend in seconds

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Future versions of the program are under construction!!!

In particular the next new version will include:

Sediment mixtures

Deposition processes downstream the dam

Work in process

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ReferencesCantelli A., Paola C., Parker G.Experiments on upstream-migrating erosional narrowing and widening of an incisional channel caused by dam removalWater Resour. Res., Vol. 40, No. 3, W03304 10.1029/2003WR002940 31 March 2004(a pdf version of the paper can be requested by clicking on the hyperlink “Order WRR-7” at http://cee.uiuc.edu/people/parkerg/order_pdf_reprints.htm)

Wong M., Cantelli A., Paola C. and Parker G.Erosional narrowing after dam removal: Theory and numerical model. River Restoration and Urban Streams Symposium, EWRI.(June 27-July 1, 2004, Salt Lake City, Utah, USA: a pdf version of the paper can be downloaded by clicking on the link “DamRemNarrow” at:http://cee.uiuc.edu/people/parkerg/conference_reprints.htm )

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The information on this site is subject to a disclaimer notice. Thank you for visiting the National Center for Earth Dynamics Web site and reviewing our disclaimer notice. The Web site is for informational purposes only and is not intended to provide specific commercial, legal or other professional advice. It is provided to you solely for your own personal use and not for purposes of distribution, public display, or any other uses by you in any form or manner whatsoever. The information on this Web site is offered on an “as is” basis without warranty. The readers of the information assume all risks from using the information provided herein.

This tool is provided free of charge. Use this tool at your own risk. In offering this tool, the following entities and persons do not accept any responsibility or liability for the tool’s use by third parties:

• The National Center for Earth-surface Dynamics;

• The universities and institutions associated with the National Center for Earth-surface dynamics; and

•The authors of this tool.

Users of this tool assume all responsibility for the tool results and application thereof. The readers of the information provided by the web site assume all risks from using the information provided herein. None of the above-mentioned entities and persons assume liability or responsibility for damage or injury to persons or property arising from any use of the tool, information, ideas or instruction contained in the information provided to you.

Disclaimer Notice

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Want more information?

For more information on this tool or the NCED Stream Restoration Toolbox please contact the author of this tool, Alessandro Cantelli, or the NCED Stream Restoration Project Manager, Jeff Marr at marrx003@umn.edu

National Center for Earth-surface Dynamics2 3rd Ave SE,

Minneapolis, MN 55414612.624.4606