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A Decade of Geomorphic and Hydraulic Response to the La Valle Dam Project, Baraboo River, Wisconsin

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  • Paper No. JAWRA-12-0244-P of the Journal of the American Water Resources Association (JAWRA).
  • Discussions are open until six months from print publication.

Abstract

We investigate stream response to the La Valle Dam removal and channel reconstruction by estimating channel hydraulic parameter values and changes in sedimentation within the reservoir. The designed channel reconstruction after the dam removal included placement of a riffle structure at the former dam site. Stream surveys undertaken in 1984 by Federal Emergency Management Agency and in 2001 by Doyle et al. were supplemented with surveys in 2009 and 2011 to study the effects of the instream structure. We created a model in HEC-RAS IV and surface maps in Surfer© using the 1984, 2009, and 2011 surveys. The HEC-RAS IV model for 2009 channel conditions indicates that the riffle structure decreases upstream channel shear stress and velocity, causing renewed deposition of sediment within the former reservoir. We estimate by 2009, 61% of former reservoir sediments were removed during dam removal and channel reconstruction. Between 2009 and 2011 renewed sedimentation within the former reservoir represented approximately 7.85% of the original reservoir volume. The HEC-RAS IV models show the largest impacts of the dam and riffle structure occur at flood magnitudes at or below bankfull. Thus, the riffle and the dam similarly alter channel hydraulics and sediment transport. As such, our models indicate that the La Valle Dam project was a dam replacement rather than a removal. Our results confirm that channel reconstruction method can alter channel hydraulics, geomorphology, and sediment mobility.

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