On December 11, 2010. Shannon White, Ben Dickinson and myself surveyed a reach of Crab Creek in Christiansburg, Virginia. The reach was located in front of the newly developed aquatic center off of Franklin street. The reach was highly modified for the creation of the aquatic center, with huge culverts being built on either end of the reach for the creation of a parking lot and road crossing. The banks were stabilized with massive amounts of rip rap and underground sewers ran the length of the reach on both sides.
A sketch of the reach from my notes
The reach of Crab Creek was approximately 60 meters long and approximately 2 meters wide. It had 4 small riffles and 2 pools connected by several runs. Vegetation only consisted of grasses planted from construction. The channel appeared highly entrenched with no room to meander between the two culverts. There was no large woody debris or other types of structure for fish communities, but several schools of fish were observed in the two pools. We were not able to catch any fish, but were able to identify stonerollers and some type of dace as the fish in the schools.
Our crew decided to measure and develop cross section profiles at one riffle and one pool. We also did a pebble count consisting of ten pieces of substrate from each of 4 riffles and 2 pools. We determined bankfull from the noticeable change in vegetation type and the fact that grasses located within the channel were still pushed over from a recent high water event. These are some of my notebook entries from the survey.
Our results gave us these two cross-section profiles.
The results indicate that the d50 substrate size of the reach is about 23 millimeters. The cross sectional profiles indicate a highly entrenched reach and it is almost completely straight indicating very low sinuosity. USGS did not have flow data for this stream, but from the looks of things, it was at median to base flow at the time of our survey. The water appeared very clear. Human have definitely altered this reach, but at least the culverts are large enough for fish and macroinvertebrate passage. The banks are definitely stable, but only because of all the rip rap. A biologist might suggest some in-stream structures like large woody debris for the stream fish to have for cover. Some riparian buffers might also be nice...and some trees on the banks for shade and aesthetics.
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