Presenter/s: Phil Roni
Symposium Session: 2024 - 05 Doing More with Less for the Love of Monitoring
Topics covered: adaptive management and monitoring
ABSTRACT
River restoration efforts continue to grow in size and complexity and several large projects covering 5 km, 10 km, or longer channel lengths have been implemented or are currently in the planning stages. However, monitoring protocols and programs have not been designed to monitor restoration effectiveness at this broad scale. The Middle Entiat Project implemented in 2019 and 2020 represented a unique opportunity to monitor physical and biological responses to a large restoration project (about 8 km) and test new and efficient effectiveness monitoring techniques. In 2018, we implemented a monitoring program to answer the following questions:
Did the restoration in the Middle Entiat increase habitat complexity, pool frequency, wood cover, side channel area and length, channel morphology, and floodplain connectivity?
What are the seasonal patterns of fish habitat use, and have juvenile and adult fish capacity increased following restoration?
How has the total area of suitable habitat for juvenile Chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss changed following restoration?
Did specific restoration design elements meet their objectives?
The trigger for post-restoration monitoring hitting a flow target (bankfull flow of 24 hours or more), which occurred in 2022. We collected pre- (2018) and post-restoration (2022) data including: 1) detailed geo-referenced fish-habitat surveys, 2) channel and floodplain geomorphic assessment based on bathymetric LiDAR, 3) quantification of large wood (LW) using satellite imagery, 4) census of summer low-flow juvenile fish abundance, and 5) as-built surveys to quantify changes in topography and morphology from restoration rather than construction.
Comparison of fish habitat survey data before and after restoration demonstrated that most pool and habitat metrics improved from 20% to 40%. Floodplain and geomorphic metrics calculated primarily from remotely sensed data and hydraulic model outputs also showed that bankfull area (84%), bankfull width (31%), floodprone width and area (10%), sinuosity (21%), river complexity index (47%), and length and area of side channels at high flows (79% and 40%) all increased following restoration. Total juvenile Chinook and steelhead abundance increased from 573 to 2782 and 80 to 544 fish before and after restoration, respectively. Total juvenile Chinook and steelhead capacity based on the 90th percentile of fish densities suggest that reach capacity increased 32% and 26% for juvenile Chinook and steelhead, respectively. Habitat suitability modeling based on showed that total weighted usable area increased for juvenile and spawning Chinook and steelhead at base flows (130 cfs), two-year flows (2,680 cfs), and spawning flows (130 cfs and 660 cfs).
Our evaluation of design objectives indicates that most bar and apex jams are meeting two or more of their design objectives. The constructed perennial side channel and some seasonal side channels were meeting their design objectives at high flows but many were disconnected or dry at low flows. The Middle Entiat case study demonstrated that simple before and after monitoring using remotely sensed data coupled with targeted field data collection can be used to evaluate not only the physical and biological success of large floodplain projects but also individual design elements.