8112

• UCREFRP Catalog Number: 8112
• Author: Osmundson, D. B. and B. K. Scheer.
• Title: Monitoring Cobble-Gravel Embeddedness in the Streambed of the Upper Colorado River, 1996-1997.
• USFW Year: 1998.
• USFW - Doc Type: Grand Junction, CO.
• Copyright Material: NO

are additional measurements that could be made that may provide a better picture of
interstitial void space. The barrel sampler (Milhous et al. 1995) reliably samples surface and
subsurface materials in gravel- and cobble-bed rivers. Also, bulk density can be used to
monitor relative changes in void space: an increase in weight of a bed sample indicates loss of
voids. Similarly, water displacement can be used to measure void volume in river bed
samples. These techniques are relatively time consuming; however, limited use of one or
more of these methods concurrent with depth-to-embeddedness sampling may provide a
predictive relationship between depth-to-embeddedness and void volume.
We did not encounter sandy areas between rocks of the surface layer as one might encounter
in areas of high embeddedness. Thus, our Wolman pebble counts used to describe the
particle size distribution of the surface layer were able to deal exclusively with particles > 8-
10 mm in diameter. If future monitoring reveals high intrusion of fines between rocks of the
surface layer, some additional technique will need to be applied to provide some measure of
the area of silt or sand between rocks.
As previously mentioned, a March date should be added to the annual sampling regime. This
would allow determination of sedimentation over winter and would better isolate the time of
greatest flushing during runoff.
To better define the relationship between embeddedness and food availability for fish species
of concern, it is recommended that appropriate biological sampling be done concurrently with
embeddedness monitoring. Time and funding constraints did not allow such sampling during
the current study. This sampling should be designed to address the following question:
How does the productivity of key invertebrate species (those used as food by target fish)
respond to changes in substrate embeddedness? Combined with fish food habit data, a
physical process-biological response model could be developed for fish carrying capacity in
much the same way that the Harvey et al. (1993) model links flows and geology to Colorado
squawfish spawning site selection. Knowledge of the carrying capacity of various reaches is
the missing link in determining realistic recovery goals for the endangered fish.
We recommend that:
1) monitoring be continued for the next several years using the protocol described here,
2) an additional sampling date during March or early April be included in the sampling
design, and
3) monitoring of mean standing stock biomass of key invertebrates (determined from fish
food habit studies) be conducted concurrently with embeddedness monitoring.
29