David L. Freyberg, a Stanford University professor of civil and environmental engineering, has sought to better understand the interplay of natural processes and human actions in aged "human-altered" river systems. His investigations focus on the Searsville Dam and reservoir, which is located within Stanford's Jasper Ridge Biological Preserve.

Freyberg's research couples field observation with the development of analytical and predictive mathematical modeling tools. The studies hope to gain meaningful conclusions about the complex web of hydrologic, geomorphologic, ecologic, and socioeconomic components in the Searsville Dam and Reservoir system as a model for decision-making about old dams more generally. The mathematical models utilize the data collected in field studies to simulate the reservoir system's response to a variety of changes, both short and long term.

Freyberg's study can be divided into two main areas of investigation. The first looks at the hydrologic interactions between a reservoir, its inflowing streams, and trapped and deposited sediment; in other words, how water flows through the system. The second investigation explores sediment accumulation in aging reservoirs and mobilization upon dam alteration or removal. While the investigations center on the Searsville Dam and Reservoir, the findings have implications for other aging dams and reservoirs.

At the March 16, 2010 Woods Institute Freshwater Salon Associate Professor David Freyberg discusses managing ecosystems and water flow in aging reservoirs. - video credit: Justin Warren, Woods Institute

Hydrologic Interactions in Aging Reservoirs

This study focuses on understanding the movement of water in the subsurface and how it is related to surface

Project: Managing water sediment and ecosystems in aging reservoirs: planning for dam removal or renewal water flow over a range of time scales. The field observations began in 2003 with the installation of a network of piezometers (wells used to measure the local energy of pore water in sediments).

Through regular observations of precipitation, evaporation, stream flow, reservoir surface elevation, and water levels in the piezometers, a number of novel hydrologic behaviors have been observed: 

  •  Groundwater responds very rapidly to precipitation events
  •  Water elevation in piezometers fluctuates on a daily basis in a complex pattern in response to transpiration (evaporation from plants) and coupled evaporation from the reservoir surface
  •  The path of water flow can change significantly over the course of the year and can be either from the sediments to the reservoir, vice versa, or both.

In keeping with Freyberg's general research approach, a mathematical model has also been developed to complement the field campaign. The bulk of this model was created by former Ph.D. student Ting Fong May Chui, now an assistant professor of National University in Singapore. The purpose of the model is to capture the complex and dynamic interactions between the reservoir and the surrounding groundwater in the deposited sediments. Rather than directly developing a Searsville- specific model, May first set out to explore some of the general challenges in modeling groundwater-reservoir systems. Ongoing model work by Ph.D. student Jun Young Kim includes simulating the Searsville hydrologic system to better understand its current behavior and to also predict its responses to different management and investment decisions.

Sediment Behavior in Aging Reservoirs and Their Channels

The goal of this research group is to better understand the conditions surrounding sediment deposition and erosion in aged, sediment-filled reservoirs. Furthermore, it explores how the removal or alternation of dams affects the underlying sediment environment. Through fieldwork coupled with software modeling, this project seeks to improve upon models currently used for how sediment becomes trapped in reservoirs. This study is comprised of two main subareas of focus.

Graduate student Jake Krall has centered his research on the nature of sediment deposition in aged reservoirs. He is working in conjunction with the U. S. Geological Survey in Santa Cruz to apply an isotope dating methodology to Searsville sediments to better understand the depositional history. In addition, he is experimenting with software to determine its usefulness as a sediment deposition predictive tool.

A second graduate student, Spencer Sawaske, focuses on sediment erosion processes and their effects on fish mobility. Sawaske is exploring the possibility of designing a controlled field experiment to study knick-point migration. Knick-points are zones of relatively sharp slope change that characterize erosion of sediment deposits. Design of this experiment remains in the early stages. Searsville provides a unique opportunity to study these processes due to the substantial sediments deposited in the reservoir and ability to control outflow. As with all projects underway at Searsville, mathematical modeling will play an important part in the design of this field experiment.

Going Forward

The complex web of private and public benefits and costs of dams and reservoirs makes decision-making challenging. It is the goal of our research to facilitate this decision-making through enhanced knowledge of the behavior of human-altered river systems. Through the combination of more sophisticated data collection processes, along with further developed mathematical models, Freyberg and his research team hope to provide decision-makers with useful analytical and predictive tools for addressing the issue of aging dams and reservoirs throughout California and beyond. This will allow decision-makers to more accurately assess infrastructure costs and the economic costs of maintenance, rehabilitation, and renewal, as well as the less-quantifiable costs to fisheries, sediment circulation, recreation, aesthetics, and natural flood control.

By Anthony Aerts