Timothy J. Randle

A MANAGED FLOOD ON THE COLORADO RIVER: BACKGROUND, OBJECTIVES, DESIGN, AND IMPLEMENTATION

The Colorado River ecosystem in lower Glen Canyon and throughout Marble and Grand Canyons was greatly altered following closure of Glen Canyon Dam in 1963, as flood control and daily fluctuating releases from the dam caused large ecological changes. Ecosystem research was conducted from 1983 through 1990, and intensively from 1990 through 1995 when dam releases were modified both for scientific purposes and protection of the river ecosystem. High flows (e.g., beach/habitat building flows) were included in the Glen Canyon Dam Environmental Impact Statement (EIS), which identified a preferred strategy for dam operations and protection of the downstream ecosystem. Use of high flows partially fulfills recommendations of many river and riparian scientists for return of more natural flows, as part of initial efforts in river restoration. In 1996, a seven-day experimental controlled flood was conducted at Glen Canyon Dam to closely study the effects of a high flow event equivalent to those proposed for future da...

Nearshore Restoration of the Elwha River Through Removal of the Elwha and Glines Canyon Dams: An Overview

Abstract Removal of two dams from the Elwha River is a unique restoration opportunity. In place for over 95 years, the dams have contributed to changes in the river, its estuary, and marine areas off shore from the river mouth, largely through reductions in sediment supply and salmon populations. Impending removals of both dams will only restore part of the severely degraded Elwha nearshore, where additional large scale anthropogenic impacts will remain. The effects of lower river levees, marine bluff hardening including significant riprapping of the marine shoreline, among other lesser habitat alterations, will continue beyond dam removal. Understanding the relationship of dam removal to the adjacent nearshore area is critical to the design of additional work necessary for successful ecosystem recovery. We provide an overview of the Elwha nearshore and collaborative efforts underway to understand it, and the role it plays in ecosystem restoration. Dam removal is slated to begin in the next 3 to 5 years making timing of this sorely needed nearshore work critical.

Dam removal: Listening in

Dam removal is widely used as an approach for river restoration in the United States. The increase in dam removals—particularly large dams—and associated dam-removal studies over the last few decades motivated a working group at the USGS John Wesley Powell Center for Analysis and Synthesis to review and synthesize available studies of dam removals and their findings. Based on dam removals thus far, some general conclusions have emerged: (1) physical responses are typically fast, with the rate of sediment erosion largely dependent on sediment characteristics and dam-removal strategy; (2) ecological responses to dam removal differ among the affected upstream, downstream, and reservoir reaches; (3) dam removal tends to quickly reestablish connectivity, restoring the movement of material and organisms between upstream and downstream river reaches; (4) geographic context, river history, and land use significantly influence river restoration trajectories and recovery potential because they control broader physical and ecological processes and conditions; and (5) quantitative modeling capability is improving, particularly for physical and broad-scale ecological effects, and gives managers information needed to understand and predict long-term effects of dam removal on riverine ecosystems. Although these studies collectively enhance our understanding of how riverine ecosystems respond to dam removal, knowledge gaps remain because most studies have been short (< 5 years) and do not adequately represent the diversity of dam types, watershed conditions, and dam-removal methods in the U.S.

Channel-planform evolution in four rivers of Olympic National Park, Washington, USA: the roles of physical drivers and trophic cascades

Identifying the relative contributions of physical and ecological processes to channel evolution remains a substantial challenge in fluvial geomorphology. We use a 74-year aerial photographic record of the Hoh, Queets, Quinault, and Elwha Rivers, Olympic National Park, Washington, USA, to investigate whether physical or trophic-cascade-driven ecological factors – excessive elk impacts after wolves were extirpated a century ago – are the dominant drivers of channel planform in these gravel-bed rivers. We find that channel width and braiding show strong relationships with recent flood history. All four rivers widened significantly after having been relatively narrow in the 1970s, consistent with increased flood activity since then. Channel planform also reflects sediment-supply changes, evident from landslide response on the Elwha River. We surmise that the Hoh River, which shows a multi-decadal trend toward greater braiding, is adjusting to increased sediment supply associated with rapid glacial retreat. These rivers demonstrate transmission of climatic signals through relatively short sediment-routing systems that lack substantial buffering by sediment storage. Legacy effects of anthropogenic modification likely also affect the Quinault River planform. We infer no correspondence between channel evolution and elk abundance, suggesting that trophic-cascade effects in this setting are subsidiary to physical controls on channel morphology. Our findings differ from previous interpretations of Olympic National Park fluvial dynamics and contrast with the classic example of Yellowstone National Park, where legacy effects of elk overuse are apparent in channel morphology; we attribute these differences to hydrologic regime and large-wood availability. Published 2016. This article is a U.S. Government work and is in the public domain in the USA

Avoiding The Inevitable? Capacity Loss From Reservoir Sedimentation

The inexorable loss of capacity of the nations reservoirs—sooner or later threatening water supplies for municipal, agricultural, and industrial uses—is but one of a number of deleterious effects wrought by sediment deposition. Trapped sediments can also damage or bury dam outlets, water intakes, and related infrastructure. Downstream effects of sediment capture and retention by reservoirs can include channel and habitat degradation and biotic alterations.

Modelling of meander migration in an incised channel

Abstract An updated linear computer model for meandering rivers with incision has been developed. The model simulates the bed topography, flow field, and bank erosion rate in an incised meandering channel. In a scenario where the upstream sediment load decreases (e.g., after dam closure or soil conservation), alluvial river experiences cross section deepening and slope flattening. The channel migration rate might be affected in two ways: decreased channel slope and steeped bank height. The proposed numerical model combines the traditional one-dimensional (1D) sediment transport model in simulating the channel erosion and the linear model for channel meandering. A non-equilibrium sediment transport model is used to update the channel bed elevation and gradations. A linear meandering model was used to calculate the channel alignment and bank erosion/accretion, which in turn was used by the 1D sediment transport model. In the 1D sediment transport model, the channel bed elevation and gradations are represented in each channel cross section. In the meandering model, the bed elevation and gradations are stored in two dimensional (2D) cells to represent the channel and terrain properties (elevation and gradation). A new method is proposed to exchange information regarding bed elevations and bed material fractions between 1D river geometry and 2D channel and terrain. The ability of the model is demonstrated using the simulation of the laboratory channel migration of Friedkin in which channel incision occurs at the upstream end.

GUIDELINES FOR ASSESSING SEDIMENT-RELATED EFFECTS OF DAM REMOVAL

Dam removal is becoming more common in the United States as dams age and environmental concerns increase. Sediment management is an important part of many dam removal projects, but there are no commonly accepted methods to assess the level of risk associated with sediment stored behind dams. Therefore, the interagency Subcommittee on Sedimentation (SOS) is sponsoring the development of a decision framework for assessing sediment-related effects from dam removals. The decision framework provides guidance on the level of sediment data collection, analysis, and modeling needed for reservoir sediment management. The framework is based on criteria which scale the characteristics of the reservoir sediment to sediment characteristics of the river on which the reservoir is located. To assist with the framework development, workshops of invited technical experts from around the United States were convened October 2008 in Portland, Oregon and October 2009 in State College, Pennsylvania. The decision framework developed at these workshops is currently being validated with actual dam-removal case studies from across the United States including small, medium, and large reservoir sediment volumes. This paper provides the latest thinking on key components of the guidelines. The paper represents contributions from over 26 entities who have participated in the development of the guidelines. After completion of the case study application, the framework will be finalized and published.

Assessing Sediment‐Related Effects of Dam Removals: Subcommittee on Sedimentation: Sediment Management and Dam Removal Workshop; Portland, Oregon, 14–16 October 2008

For a host of reasons including dam safety, maintenance costs, and ecological concerns, more dams are currently being removed each year in the United States than are being constructed. Because many reservoirs have accumulated sediments within their pools, dam removal can potentially impose a variety of sediment-related risks, including downstream effects on habitat, water quality, infrastructure, and flood storage. Sediment-related risks are particularly heightened when the sediment stored behind a dam is contaminated.

Elwha River Restoration: Sediment Modeling

The National Park Service, with technical support from the Bureau of Reclamation, is in the process of removing Elwha and Glines Canyon Dams on the Elwha River near Port Angeles, Washington to restore anadromous fish and the natural ecosystem and areas of cultural significance to the Lower Elwha Klallam Tribe. Elwha Dam was completed in 1913 and forms Lake Aldwell. Glines Canyon Dam was completed upstream in 1927 and forms Lake Mills. These two dams are the largest ever removed. These dams are being removed concurrently in controlled increments over a three-year period, which began on September 17, 2011. As of July 2010, reservoir sedimentation for the two lakes was estimated to be 24 million yd 3 , of which 20 million yd 3 are stored in Lake Mills. Reservoir sediment is being eroded and redistributed by the river as the dams are removed and the reservoirs are drawn down. This paper describes a mass balance numerical model that is being used as part of the sediment adaptive management and monitoring program. This program is presently being implemented to compare measured effects with predictions and recommend corrective actions if necessary. Facilities have been constructed for water quality and flood protection to mitigate for sediment effects, including water treatment plants, new wells, a new surface water intake, raising the height of existing levees, and the construction of new levees. The sediment effects of dam removal have been predicted based on a drawdown experiment of Lake Mills, numerical modeling, and physical laboratory modeling. A numerical mass balance model was developed for use during the adaptive management program to provide up-to-date predictions based on changing hydrology and dam removal schedules. In addition, the numerical model is also being used to help guide monitoring activities and synthesize monitoring data.

Bridging the Gap between Numerical Sediment Modeling and Reality for Dam Removal Investigations

Dam removal projects are becoming increasingly common, yet the accuracy of quantitative sediment predictions remains uncertain. This situation results because of a general lack of scientific monitoring during dam removals, and the fact that the majority of dams that have been removed are small in size. Resource managers dealing with dam removal projects rely heavily on results from predictive numerical modeling to assess environmental impacts on the human environment. If the models are not properly applied, predicted impacts can be erroneous. This paper provides some guidance for the application of numerical sediment transport models to improve their accuracy and utility for dam removal investigations.