Bureau of Reclamation’s Grant for Sustainable Pool-Riffle Morphology in River Restoration

Criteria and knowledge gained from this research project have the potential to provide design guidelines, assess the need for engineered features as well as provide a means for determining design success metrics.

These mitigation efforts include the design of specific habitat features for several life stages of salmonids in various streams or rivers identified throughout the Northwest.

In addition to a field survey to identify the effectiveness of the Caamaño velocity reversal criterion, a physical model of a pool riffle sequence will be developed. The purpose of the physical model will be to measure and monitor the jet flow through pool and riffle features under varying conditions. The flume allows study of the velocity reversal phenomena in concert with sediment deliveries that cannot be accomplished safely or effectively in the field. This model would also afford the opportunity to validate measured field data in addition to numerically modeled output of a pool riffle sequence.

The river cross sectional shapes, at any location along the watercourse, are a function of the flow,
the quantity and character of the sediment in movement through each section, and the character
or composition of the materials making up the bed and banks of the channel (Leopold et al. 1964;
Knighton, 1998; Federal Interagency Stream Corridor Restoration Working Group, 1998). Poolriffle sequences are one of the possible river reach morphologies created by these interactions.
Many restoration projects attempt to restore pool morphology in a sustainable and minimum
maintenance manner. This proposal addresses three important aspects of the restoration design
and assessment:
1. The design of sustainable pools in a restoration project requires either an empirical analysis (such as the Rosgen methodology) or a full 3 dimensional hydrodynamic and sediment transport model. For the latter analysis, few projects have the budget to conduct a thorough modeling approach.
2. When selecting reaches for restoration or deciding whether a particular feature within a
restoration reach should be left untouched, it is important to have a methodology for assessing whether the pool will be stable with or without engineering features.
3. There is increasing external pressure to develop performance criteria for assessing the success of stream restoration projects (for example, Bernardt et al., 2005). To minimize resources in these performance metrics, it is very useful to have indicators that are quickly and easily assessed in the field (Palmer et al., 2005, Federal Interagency Stream Corridor Restoration Working Group,
1998).

In order to verify these criteria over a broader range of field conditions, the following
tasks are proposed:
Activity 1: Field Verification of Pool Sustainability Criteria: Six Reclamation restoration projects will be selected and the pool sustainability criteria will be tested for projects in the Northwest.
Activity 2: Laboratory Verification: The criterion assumes the gravel bed river is supply limited. This is usual for most systems but undisturbed watersheds (for example logging, development, grazing or wildfire can alter this balance). To assess the response of the pool to sediment pulses or artificially high sediment loads it is necessary to measure the differential sediment transport between the pool and riffle. This is very difficult and hazardous to do in the field at the high flow conditions when the geomorphically significant sediment transport is occurring. To investigate the relevance of the simple criteria in high sediment delivery systems and whether the simple criterion should be modified under conditions of high sediment loads, a laboratory simulation sediment transport through a pool-riffle sequence will be simulated in the large-scale flume at the Idaho Water Center located in Boise, Idaho.