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The Rothrock's Mill field site is located off Highway 62 west of Corydon, Indiana. Heading west on Hwy 62, turn right on Harrison Spring Road. Take a left at every major intersection until reaching the site. This site was evaluated at 1:15 P.M. EDT on September 14, 1999. The weather was pleasant and sunny, with an air temperature of 85 F. The Stream's water level appeared much lower than normal due to drought conditions.
This site's accessibility was easy because this is a popular stopping point for canoers coming from Cave Country Canoes located in Milltown. There was a parking area within 100 yards of the riffles that were studied. This made the transport of the equipment needed to study the riffles easy.
Rothrock's Mill's physiographic region is the Highland Rim Natural Region, Mitchell Karst Plain section, bordering the Escarpment section of the Shawnee Hills Natural Region. This region is a bedrock community described as having sink-holes, a lot of silt present due to weathered limestone, and medium as well as high gradient streams and rocky bottoms. Common plant life in this region includes water willow, pin oak, swamp white oak, sycamore, red maple and sweet gum.
The general area included secondary growth climax forest. There was little to no canopy cover over the riffles that were studied. The vegetation stability was rated as good due to the amount of vegetation and large rocks that covered the banks. This allows for only minor erosion. The area has changed considerably in the last 15 years. In 1986, for example, because of the removal of the dam located at this site, a previous group studying darters had to move to riffles well downstream. When the dam was taken out, silt from the mill pool had washed out and covered the entire streambed. Now much of this silt has washed away revealing the rocks underneath.
The riffle at Rothrock's Mill is one of the same sites that was studies in 1995. During the present study, the riffle was approximately 14 ft. wide and 40 ft. in length. The width of the river itself was 32 ft. The average depth at the riffle was 6.59 in. with a maximum depth of 13 in. The average riffle velocity was 3.5 ft. per second. The discharge was approximately 133 cubic ft. per second.
The results of the water quality testing indicated an ample amount of dissolved oxygen (12 mg/L) and an alkaline pH (8.4). The riffle had a conductivity of 0.36 mS/cm suggesting substantial levels of dissolved solids in the water. Fecal coliform tests turned out to be zero. Tests for phosphates and nitrates were not performed at this site.
Looking upstream from the riffle, one would observe much slower water gliding toward the riffle area. In the past, this was the mill pool; so the stream character has been altered in the past 15 years. Riparian trees upstream included mostly sycamore and maple. The bank and a portion of the streambed were very dry, and there was a convenient walking path located on the east bank. This area had a substantial coverage of small Asiatic clam and fresh-water mussel shells.
Looking downstream, there were some large rocks from the abandoned mill dam on both sides of the river. Beyond the old dam site, there were several riffles and pools. We seined these riffles and pools, but no additional spotted, bluebreast or variegate darters were found. There were many large rocks on the east bank and trees shading the west bank. This canopy did not extend over the river to a measurable extent however. Large stands of water willow lined the banks providing habitat foe sunfish. Additionally, there was a gravel outwash community on the right hand side. Instream structures such as logs and brush provided some fish habitat as well. There were rootwads along the banks, but these were exposed at the time of this study. Leaf detritus was accumulating from fall leaf drop, and leaf packets were found lodged against the rocks. Also, immediately downstream from the site is a strip of seasonal cabins and some permanent residences. Farther downstream, cattle range near the river.
The bed of the riffle studied was comprised mostly of cobble and rocks. They were moderately easy to displace by kicking and prying. The water was very clear and there was a relatively small amount of epifaunal colonization. The findings of the TKN samples included mayfly nymphs, stonefly nymphs, Dobson fly larvae, caddis fly larvae, damsel fly larvae, gray midge larvae, water pennies, riffle beetles, crayfish, right handed snails, Asiatic clams and aquatic worms. This resulted in an overall water quality index of 30, which is excellent.
During the examination of the area, a significant number of fish was noted just upstream from the old dam site at the riffle studied. It appeared that the fish were concentrated there by the low water conditions. In this riffle, spotted, bluebreast, variegate, greenside and banded darters were easily collected. The incidental catch included brindled madtom catfish, stonecats, stonerollers and banded sculpin.