The Stream Restoration Toolbox

2. 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.

3. 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.

4. Title Page Tool Title: The Dam Remover: Mark 1 Tool Author: Alessandro Cantelli, PhD. Author e-mail: Alessandro.Cantelli@shell.com Version: 1.0 Associated files: 1) DamRemoverMARK1.ppt 2) DamRemoverMARK1.xls Date: February 2006

5. Outline of this Document • 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

6. Warnings on tool limitations • 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.

7. Introduction to the tool • 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.

8. This tool is related to this issue. 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); • Reservoirs behind dams are filling with sediment and losing their effectiveness; • Rivers returned to their natural state may have positive economic and social benefits.

9. 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

10. 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/

11. 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 NASA https://zulu.ssc.nasa.gov/mrsid/mrsid.pl From Gary Parker’s e-book http://cee.uiuc.edu/people/parkerg/

12. 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. Matilija dam during flood event Upstream face of Matilija dam, sediments are adjacent to the structure Courtesy http://pages.sbcglobal.net/pjenkin/matilija/

13. Tool Overview 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.

14. Narrowing versus widening 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.

15. Experiments - Data On the left: sketch of the facility. On the right: photo of the flume used. front_view.mpg and plan_view.mpg : to run without relinking, download to same folder as this PowerPoint presentation. Flow View from downstream Overhead View FRONT

16. Time evolution of the channel long profile after dam removalThe observed time evolution of the longitudinal profile is shown in this plot. For the non-cohesive material 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 delta front. This result provides one of the boundary conditions used in the tool.

17. Time evolution of the width of the channel water surface at various points upstream of the dam after removal 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 of the inlet section. rapid narrowing slow widening

18. Experiments: General Observations • 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.

19. Introduction to DamRemovalMARK1.xls • 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.

20. The Conceptual Model 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.

21. The Model and the Approximations • 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 width • Flow Hydraulics • Flow conditions approximated as normal (uniform and steady) • The Manning-Strickler flow resistance relationship is used. • Theshear 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 j.

22. The Model and the Approximations • 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.

23. The Model and the Approximations 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 coordinate Ss = side slope of the channel banks (constant value) H = water depth of the bed region (defining the active channel) Bb = half the channel bed width Bw = half the channel top width Bs = width of one sidewall region (including both submerged and emergent banks) hb = bed elevation on the bed region ht = elevation of the top of the active channel he = elevation of the top of the channel bank L = bank arc length normal to flow direction. Conceptual model for erosional narrowing Cross-section at time t: solid line cross-section at time t+Dt: dashed line.

24. The Model and the Approximations qbs denotes the total volume bedload transport rate per unit width in the streamwise direction qbndenotes 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 narrowing Cross-section at time t: solid line cross-section at time t+Dt: dashed line.

25. Initial and Boundary Conditions • 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. Flow A B Hd 2 Hd C ABD = Deltaic deposit ABC = Part of the deltaic deposit treated in the model D

26. C C IMPORTANT: In the case of “staged removal” the point C is represented by the crest of the dam. Flow A B Hs Hd D ABD = Deltaic deposit ABC = Part of the deltaic deposit treated in the model

27. 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. A Initial Channel Width A Initial Longitudinal bed profile B B C Sketch of the initial trapezoidal channel above the deltaic deposit Pivot axis C

28. Using the Excel workbookDamRemovalMARK1.xls Worksheet “Auxiliary Parameters” These parameters need to be input before starting the calculation. The parameters are discussed in the Appendix

29. 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 steps Is automatically calculated. Worksheet “Initial Topography”

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

31. Worksheet “Initial Topography” (continued) 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.

32. Insert Parameters Here 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”

33. 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.

34. 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.

35. Using the tool: Three examples • 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. • Laboratory scale with a characteristic stramwise length of about 10 m and a height of about 30 cm. • Small dam scale with a characteristic streamwise length of about 100 m and a height of about 3 m. • Medium size dam scale with a characteristic streamwise length of about 1 km and a height of about 30 m.

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

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

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

39. Laboratory scale: results for long profile Legend in seconds

40. Laboratory scale: results for channel width Legend in seconds

41. Laboratory scale: results for water depth Legend in seconds

42. Laboratory scale: results for volume sediment transport rate/unit width Legend in seconds

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

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

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

46. 2. Small dam scale: results for long profile Legend in seconds

47. 2. Small dam scale: results for channel width Legend in seconds

48. 2. Small dam scale: results for water depth Legend in seconds

49. 2. Small dam scale: results for volume sediment transport rate/ unit width Legend in seconds

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