Technical Report

Physical Features and Fish Distribution of a Steep Riffle Rio Grande-Bernalillo Bridge Reach

URL: https://webapps.usgs.gov/mrgescp/documents/Reclamation_2004_Physical%20Features%20and%20Fish%20Distribution%20of%20a%20Steep%20Riffle%20Rio%20Grande-Bernalillo%20Bridge%20Reach.pdf

Date: 2004/10/01

Author(s): Massong T.M., Porter M.D.

Publication: U.S. Bureau of Reclamation Report-2004, 11 p.

Abstract:

During summer routine fish sampling (September 2003) on the Rio Grande, the fish distribution changed at the second riffle downstream of the HWY 550 bridge in the city of Bernalillo (Figure 1). In fact, the marked decrease in the number of fish through this riffle suggested that fish may be avoiding the riffle altogether. On October 21-22, 2003, the riffle was again sampled for fish, plus was physically surveyed. The goal of this study is to determine if a physical feature can easily be identified in this naturally-formed riffle that explanes the decline in the local fish distribution. In this section of the Rio Grande, one restoration technique is the construction of low-head gradient control/restoration facilities (GRF). The GRF constructed upstream of this riffle on the Pueblo of Santa Ana consists of vertical sheet-pile covered with a rock apron with approximately a 2 foot head. This constructed feature is designed to create a lower-sloped section upstream. Ideally, the structure mimics a riffle with an upstream run/pool. The current concern with the construction of a GRF is that although the GRF itself is not designed to be fish habitat, the area upstream of the GRF is designed to improve habitat. Since the initial fish data collected in September suggested that the channel immediately upstream of the naturally forming riffle was avoided by the fish, the channel upstream of the GRF could also be river avoided by fish.

The riffle studied is approximately 350 meters downstream of the NM Hwy 550 bridge (Figure 1). The approximate flow at the time of survey was 125-150 cubic feet per second (cfs). The Rio Grande in this section has a gravel to cobble bed with sand deposits on top of the banks. Channel incision since 1992 has created a single-threaded low flow channel, with a network of high flow channels (Massong, 2003). A low-flow, gravel riffle-plane bed morphology (Montgomery and Buffington, 1998) is the current planform present. The thalweg migrates slightly within the active low-flow channel.

Specific study objectives are: 1) determine if the fish distribution data collected earlier in September was temporally anomalous through a re-sampling of the area, and 2) if the low abundance of fish continued to exist in October, evaluate the physical habitat present immediately upstream and through the riffle.