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T Figure 4. Side channel at low flow on the Yampa River diked for fish habitat enhancement at river mile 121. The rock dike in the foreground is partially beached. Table V. Percentage composition of native and non-native fishes in a designed backwater created from a partially-blocked side channel in the Yampa River, river mile 121 (n=867). Native Species Percentage Composition Non-Native Species Percentage Composition roundtail chub 18.1 redside shiner 45.4 speckled dace 8.3 fathead minnow 23.4 bluehead sucker 1.2 white sucker 2.8 flannelmouth sucker 0.4 common carp p,2 Total: 28.0 speckled dace x redside shiner 0.1 bluehead sucker x white sucker 0.1 Total : 72.0 could be similarly disadvantaged in size and face competition from native and non-native species. These designed backwaters appear to have been only par- tially successful because the dikes were breached or partially breached. This suggests that backwaters created from side channels should be formed by high non-porous and stable dikes. Also, none of the endangered fishes have been recorded recent- ly from the vicinity of these backwaters, illustrating the need for proper location and placement of these enhancements. Gravel Pits Gravel extraction is especially prevalent in the flood- plain of the Colorado River near Grand Junction, Colorado. A nearly continuous series of gravel pits now line the flood- plain. These vary in size, depth, shape and orientation to the river channel, and are of three types; those permanently open to the river, those open to the river only during high spring flows, and those permanently isolated from the river. The third type is not considered in this analysis. Most industries prefer to excavate away from [he high water line to avoid costly delays from 404 permits required by the Water Quality Act and consultation required by Section 7 of the Endangered Species Act. So, most gravel operations are conducted away from the high water line and are of the third type. Proper structural specifications are still needed for advising industries on appropriate design, and excavation and rehabilitation techniques to benefit especially native riverine fishes. Gravel pits permanently open [o the river are most commonly excavated in large midchannel islands or low flood- plains, such as the 30 Road Pit near Clifton, Colorado (Figure 5). The 1.0-ha pit was excavated from a midchannel island in 1978, leaving a horseshoe-shaped gravel berm with a downstream opening. Water circulates into the pit through the opening that was nearly sealed by shifting silt and gravel during runoff 1980. Maximum depth of this pit was 5.5 m and average depth was 1.1 m (Table VI). Silt deposits have nearly filled the rear of the backwater and covered the gravel substrate to a depth of 0.3-0.5 m. Emergent vegeta- tion has become established in the silt deposits,. and ducks and geese were seen resting and feeding in the pit in October 1980. The pit was sealed from the river in 1981, except during runoff. Fish composition when open to the river in 1980 and 1981, was dominated by non-native species (73.3%), pre- dominantly carp, red shiner, fathead minnow, sand shiner and 528 j 529 °' ~ -~- ~'. ~._-