Event Title

Addressing the Legacy Effect of Low Large Woody Debris Volumes in Wadeable Streams: HDLWD, a Low Impact, Inexpensive Approach

Presenter Information

Stephen N. Bennett

Location

Ellen Eccles Conference Center

Event Website

https://forestry.usu.edu/htm/video/conferences/restoring-the-west-conference-2014/

Abstract

A common assessment of many Pacific Northwest streams is that they have low instream complexity due to reduced large woody debris (LWD) and degraded riparian areas. A traditional approach to addressing this problem has been to use heavy machinery to install expensive LWD structures (> $50-100/m) that are engineered to be stable. In contrast, we are testing a hand-based approach called high density large woody debris (HDLWD) for adding LWD in high densities (e.g., 20-50 m between structures) that is inexpensive (< $5- 10/m), and can be built with minimal disturbance to recovering riparian areas. We use a hydraulic post driver to drive 4-6 cm diameter x 1.5 m long, non-treated, wooden fence posts into the stream bottom and banks

to secure hand-placed LWD in place. In contrast to many traditional engineered structures, we expect LWD to remain on these structures for 1-5 years, making them dynamic by design. We have built almost 550 structures covering 12 km in wadeable streams within an Intensively Monitored Watershed in southeast Washington. We developed a set of a priori hypotheses about the hydraulic and geomorphic responses the HDLWD would create and are testing these with a variety of survey methods including topographic surveys and rapid habitat surveys. We are still assessing the long-term effectiveness of the structures but we have already observed many of our hypothesized responses including: the creation of eddy pools, scour pools, undercut banks, a variety of bar types, and wood movement and trapping by the structures. After two spring flow events (2013 and 2014) 92% of the structures are remaining. The HDLWD method appears to provide an inexpensive, highly adaptable, and low impact method for addressing the legacy deficit of LWD in many small to medium sized streams until riparian areas fully recover.

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Oct 21st, 8:10 AM Oct 21st, 8:20 AM

Addressing the Legacy Effect of Low Large Woody Debris Volumes in Wadeable Streams: HDLWD, a Low Impact, Inexpensive Approach

Ellen Eccles Conference Center

A common assessment of many Pacific Northwest streams is that they have low instream complexity due to reduced large woody debris (LWD) and degraded riparian areas. A traditional approach to addressing this problem has been to use heavy machinery to install expensive LWD structures (> $50-100/m) that are engineered to be stable. In contrast, we are testing a hand-based approach called high density large woody debris (HDLWD) for adding LWD in high densities (e.g., 20-50 m between structures) that is inexpensive (< $5- 10/m), and can be built with minimal disturbance to recovering riparian areas. We use a hydraulic post driver to drive 4-6 cm diameter x 1.5 m long, non-treated, wooden fence posts into the stream bottom and banks

to secure hand-placed LWD in place. In contrast to many traditional engineered structures, we expect LWD to remain on these structures for 1-5 years, making them dynamic by design. We have built almost 550 structures covering 12 km in wadeable streams within an Intensively Monitored Watershed in southeast Washington. We developed a set of a priori hypotheses about the hydraulic and geomorphic responses the HDLWD would create and are testing these with a variety of survey methods including topographic surveys and rapid habitat surveys. We are still assessing the long-term effectiveness of the structures but we have already observed many of our hypothesized responses including: the creation of eddy pools, scour pools, undercut banks, a variety of bar types, and wood movement and trapping by the structures. After two spring flow events (2013 and 2014) 92% of the structures are remaining. The HDLWD method appears to provide an inexpensive, highly adaptable, and low impact method for addressing the legacy deficit of LWD in many small to medium sized streams until riparian areas fully recover.

https://digitalcommons.usu.edu/rtw/2014/Posters/16