Sediment storage and shallow groundwater response to beaver dam analogues in the Colorado Front Range, USA

Abstract

Enthusiasm for using beaver dam analogues (BDAs) to restore incised channels and riparian corridors has been increasing. BDAs are expected to create a similar channel response to natural beaver dams by causing channel bed aggradation and overbank flow, which subsequently raise water tables and support vegetation growth. However, lack of funding for monitoring projects post‐restoration has limited research on whether BDAs actually cause expected channel change in the Front Range and elsewhere. Geomorphic and hydrologic response to BDAs was monitored in two watersheds 1 year post‐restoration. BDAs were studied at Fish Creek, a steep mountainous catchment, and Campbell Creek, a lower gradient piedmont catchment from May to October 2018. At each restoration site, the upstream‐ and downstream‐most BDAs were chosen for intensive study in comparison with unrestored reference reaches. Monitoring focused on quantifying sediment volumes in BDA ponds and recording changes to stream stage and riparian groundwater. Despite differences in physical basin characteristics, BDA pools at both sites stored similar volumes of sediment and stored more sediment than reference pools. Sediment storage is positively correlated to BDA height and pool surface area. However, BDAs did not have a significant influence on shallow groundwater. The lack of groundwater response proximal to BDAs could indicate that local watershed factors have a stronger influence on groundwater response than restoration design 1 year post‐restoration. Systematic, long‐term studies of channel and floodplain response to BDAs are needed to better understand how BDAs will influence geomorphology and hydrology.

Beaver dam analogues drive heterogeneous groundwater–surface water interactions

“…Although few field‐based studies of BDAs exist, the link between BDA height and function has been affirmed in other work. Scamardo and Wohl (2020) found that BDA height was a significant predictor of sedimentation volume associated with the structures. These findings provide further confirmation that ability of a BDA to alter riparian processes is closely linked to BDA size.…”

Beaver dam analogue configurations influence stream and riparian water table dynamics of a degraded spring‐fed creek in the Canadian Rockies

“…In the absence of natural beaver recolonisation, dam structures intended to mimic the form and function of beaver dams, called beaver dam analogues (BDAs), are used for restoring degraded streams. BDAs are low‐tech and inexpensive, constructed to be permeable instream structures made up of branches, mud and rock (Pilliod et al, 2018; Pollock, Lewallen, Woodruff, Jordan, & Castro, 2018; Scamardo & Wohl, 2020). There are three generic BDA designs that differ in structure, materials and desired outcomes (Pollock et al, 2018; Pollock, Wheaton, Bouwes, & Jordan, 2012), sometimes referred to as standard BDAs (Scamardo & Wohl, 2020).…”

“…BDAs are low‐tech and inexpensive, constructed to be permeable instream structures made up of branches, mud and rock (Pilliod et al, 2018; Pollock, Lewallen, Woodruff, Jordan, & Castro, 2018; Scamardo & Wohl, 2020). There are three generic BDA designs that differ in structure, materials and desired outcomes (Pollock et al, 2018; Pollock, Wheaton, Bouwes, & Jordan, 2012), sometimes referred to as standard BDAs (Scamardo & Wohl, 2020). The types are: (a) starter dams—vertical posts with willow woven between the posts (wicker weave) and fill material (e.g., cobble, vegetation and mud) placed upstream, (b) post lines and wicker weave—just post lines with wicker weaves, which are highly permeable and (c) reinforced existing or abandoned natural beaver dams which involve simply reinforce existing or abandoned natural structures using vertical posts.…”

“…The types are: (a) starter dams—vertical posts with willow woven between the posts (wicker weave) and fill material (e.g., cobble, vegetation and mud) placed upstream, (b) post lines and wicker weave—just post lines with wicker weaves, which are highly permeable and (c) reinforced existing or abandoned natural beaver dams which involve simply reinforce existing or abandoned natural structures using vertical posts. Recently, Scamardo and Wohl (2020) installed two types of BDA: (a) traditional post and willow BDAs (Pollock et al, 2018) made up of few large wood posts (diameter > 0.10 m) inserted in the stream bed with thinner branches woven between posts and staked on the downstream end of BDA, and (b) non‐traditional wood‐jam BDAs built of large logs partially buried in the banks across the bed and perpendicular to flow. These BDAs were also individually dispersed structures.…”

“…BDAs have been deployed in thousands of degraded streams (Lautz et al, 2019). Similar to natural beaver dams, BDAs aggrade the channel and stream bed (Scamardo & Wohl, 2020) and thus raise water tables in the riparian area (Briggs, Lautz, Hare, & González‐Pinzón, 2013; Feiner & Lowry, 2015; Karran, Westbrook, & Bedard‐Haughn, 2018). A higher riparian water table helps support healthy riparian plant communities (Dittbrenner et al, 2018; Silverman et al, 2019; Westbrook, Cooper, & Baker, 2006) while slowing of stream water helps moderate stream temperatures (Majerova, Neilson, Schmadel, Wheaton, & Snow, 2015; Weber et al, 2017).…”