1 USACE RESERVOIR SEDIMENTATION IN THE CONTEXT OF CLIMATE CHANGE AVAILABLE RESERVOIR SEDIMENT INFORMATION Preferred Citation: Pinson, A., B. Baker, P. Boyd, R. Grandpre, K.D. White, and M. Jonas. (2016) U.S. Army Corps of Engineers Reservoir Sedimentation in the Context of Climate Change. Civil Works Technical Report, CWTS 2016-05, U.S. Army Corps of Engineers: Washington DC. i USACE RESERVOIR SEDIMENTATION IN THE CONTEXT OF CLIMATE CHANGE AVAILABLE RESERVOIR SEDIMENT INFORMATION EXECUTIVE SUMMARY The US Army Corps of Engineers (USACE) is the largest operator of dams in the United States. Each USACE dam was planned, designed and built to provide specific benefits to the American public, including navigation, flood risk reduction, hydropower generation, recreation, and water supply. Most of the USACE dams have operated for more than 50 years, with some approaching 100 years of operation. Sedimentation impacts all of these dams to varying degrees by reducing reservoir volumes over time. Even though sedimentation was taken into account in design, there may be gradual loss of functionality with respect to a dam's authorized purpose(s) over time. Since 2011, the USACE Civil Works Strategic Plan has stressed sustainable solutions for the 21st century. For our reservoirs, this requires that we take into account all of the factors that impact their performance and reliability. Among these is climate change, which has been identified as a major cause of future vulnerability to reservoirs due to its role in changing sedimentation patterns. Both observed and projected hydroclimate trends impact the rate of sediment delivery to reservoirs. Important drivers include increasing heat waves, changes in drought frequency and magnitude, altered freeze-thaw cycles, changes in snow volume and the onset of snowmelt, increased heavy precipitation, and changes in the frequency, magnitude, and duration of floods. A reservoir storage baseline is necessary to determine which reservoirs are vulnerable to increased (or decreased) sedimentation resulting from past and future changes. As part of the effort to set a reservoir sediment baseline, six USACE districts were selected for detailed analysis as a representative sample of reservoirs in a variety of environmental settings. Some reservoirs have experienced impacts from sedimentation, resulting in a loss of storage capacity for water supply, flood risk reduction, recreation and other authorized purposes. For the majority of reservoirs, repeated, accurate surveys are vital to determining current sedimentation status from which to estimate future decreases in reservoir storage due to sedimentation. Information obtained from the pilot districts was used to develop a web portal to collect and house reservoir sediment information from across the Nation, including analytical data supporting efficient and sustainable reservoir sediment management. This progress report summarizes the findings of the six pilot districts and the information housed in the new web portal. We provide recommendations on how to best achieve planned reductions in existing data gaps and how to identify the minimum survey frequency required to accurately project sedimentation impacts to reservoir project benefits. Only by understanding the rate at which sedimentation is encroaching on the authorized reservoir purposes can USACE develop plans to sustainably manage its reservoirs and maximize reservoir service life. ii USACE RESERVOIR SEDIMENTATION IN THE CONTEXT OF CLIMATE CHANGE AVAILABLE RESERVOIR SEDIMENT INFORMATION This page is intentionally left blank. iii USACE RESERVOIR SEDIMENTATION IN THE CONTEXT OF CLIMATE CHANGE AVAILABLE RESERVOIR SEDIMENT INFORMATION TABLE OF CONTENTS Executive Summary ...................................................................................................................... ii Table of Contents ......................................................................................................................... iv List of Figures ............................................................................................................................ vi List of Tables ............................................................................................................................ vii Introduction ................................................................................................................................... 8 Reservoir Sustainability and the Need for Reservoir Sedimentation Planning ...........................8 The Climate Preparedness and Resilience (CPR) Program .......................................................10 Enhancing Reservoir Sedimentation Information (RSI) for Climate Preparedness and Resilience ...................................................................................................................................11 Overview of Climate Change Impacts on Reservoir Sedimentation ...................................... 12 Review and Analysis of Reservoir Sedimentation Information (RSI) ................................... 17 Overview ....................................................................................................................................17 RSI Data Types ..........................................................................................................................17 RSI Initial Data Collection Methods .........................................................................................18 Summary by RSI Category ........................................................................................................22 Developing an RSI Update Strategy .......................................................................................... 30 RSI Update Strategy Overview ..................................................................................................30 RSI Baseline Data ......................................................................................................................30 Project Data Needs Related to Authorized Purposes .................................................................30 Navigation ..............................................................................................................................31 Flood Risk Management ........................................................................................................32 Aquatic Ecosystem Restoration .............................................................................................33 Hydropower ...........................................................................................................................34 Recreation ..............................................................................................................................35 Water Supply .........................................................................................................................35 Dry Dams ...............................................................................................................................36 Other Determinants of RSI Data Needs .................................................................................37 Geomorphology and Regional Characteristics ..................................................................37 Size .....................................................................................................................................37 Shape ..................................................................................................................................38 Basin Schemes ...................................................................................................................38 Data Needs Based on Reservoir Sustainability ..........................................................................39 Understanding Changes Over Time .......................................................................................39 Sediment Yield .......................................................................................................................40 Wildfire ..................................................................................................................................41 iv USACE RESERVOIR SEDIMENTATION IN THE CONTEXT OF CLIMATE CHANGE AVAILABLE RESERVOIR SEDIMENT INFORMATION Sediment Management ...........................................................................................................43 RSI Data Collection ...................................................................................................................45 Data Collection Methods ...........................................................................................................46 Range and Contour Methods .............................................................................................46 Topographic Data Resolution ............................................................................................47 Bathymetric and Hydrographic Survey Techniques ..........................................................48 Innovative Techniques .......................................................................................................48 Datum Requirements .........................................................................................................49 Sediment Sampling ............................................................................................................49 Data Collection Frequency ........................................................................................................50