Riparian Habitat Establishment Model (RHEM)
The establishment of riparian vegetation is an important objective for many river restoration projects. Current models for evaluating the establishment and survival of riparian vegetation are overly simplistic because they ignore the potential effects of ground water dynamics on water table elevation, rainfall as a source of plant available soil moisture, atmospheric controls on evapo-transpiration (ET) demands, and the effects of soil hydraulic properties and subsurface layering on soil moisture content in the root zone.
This Science and Technology (S&T) Program research project will perform a coordinated field study and modeling exercise to evaluate the significance of the various physical and biological processes affecting the establishment and survival of riparian vegetation with the objective of providing new methods and tools for river restoration planning and management.
Need and Benefit
The establishment of riparian vegetation is an important part of many river restoration projects. When planning such projects, a simplistic model for evaluating the success of seedling establishment and survival is typically employed. This conceptual model assumes that riparian seedlings only obtain water at the water table and that the water table elevation is equivalent to river stage. Consequently, restoration plans based on this conceptual model call for maintaining the rate of decline of river stage equivalent to the rate of seedling root growth. Since typical seedling root growth rates are on the order of one inch per day, the total quantities of water over the initial seedling growth period can be considerable.
Basic hydrologic and plant growth principles suggest that this conceptual model is overly simplistic because it ignores the potential effects of ground water dynamics on water table elevation, rainfall as a source of plant available soil moisture, atmospheric controls on transpiration demands, and the effects of soil hydraulic properties and subsurface layering on soil moisture content in the root zone above the water table.
For the RHEM, we will perform a coordinated field study and modeling exercise to evaluate the significance of the various physical and biological processes affecting the establishment and survival of riparian vegetation. The field study will focus on developing a new dataset characterizing the physical and biological properties of a point bar located on the Sacramento River. This site was selected because it is area where the California Department of Water Resources (CDWR) has installed instrumentation and collected significant amounts of data on cottonwood seedling growth and river stage relationships. It is also an area where other Reclamation researchers are collecting data for modeling channel migration and sediment transport.
Our field study will build on these studies by characterizing the physical and hydraulic properties of the point bar sediments in the field and laboratory. We will measure soil moisture content in the root zone of growing cottonwood seedlings and collect data relevant to plant transpiration. These new datasets will be used to calibrate and validate the RHEM.
The RHEM will be developed by modifying the widely used HYDRUS model to simulate the growth characteristics of cottonwood seedlings. Using the field data sets, we will calibrate and validate the RHEM model to simulate and predict measured soil water content and seedling growth observations. Upon completion of these activities, RHEM will be used to systematically evaluate the significance of the effects of ground water dynamics, rainfall, atmospheric conditions, and soil properties on the establishment and survival of riparian vegetation.
RHEM will benefit river restoration projects throughout Reclamation and in other agencies by providing basic information about the significance of and relationships between the many factors impacting the growth of riparian vegetation. It will provide documentation on methods of collecting field data and new mathematical tools for quantitatively simulating riparian habitat establishment and survival.
The following documents were not reviewed. Statements made in these documents are those of the authors. The findings have not been verified.
Riparian Habitat Establishent Model (final, PDF,
By Dr. Michael Tansey, Dr. Charles Young and Prof. James H Richards
Report completed on August 03, 2011