Neumühlewehr – Assessment of alternatives and design of two recommended solutions

In the last 100 years, about 80 grade control structures as sills were established in Emme-River, Canton Bern. The present investigation focuses on possibilities to substitute the sill “Neumühle” (Fig.1). The sill “Neumühle” is located at the Emme-River where the bridge called Neumühlesteg crosses the river.

The drop height between the upper edge of the sill and the river bed downstream is 3.20 m. In autumn 2001 the sill broke during the floods. The new structure is required to stabilise the river bed on the one hand and to guarantee a passage for the aquatic fauna on the other hand.

Several variants like a system of transverse bar structures block ramps or sills were investigated. Two solutions were selected: a system of transverse bar structures and a 7 % steep block ramp structure. As design criteria for the block ramp already exist (Whittaker and Jäggi 1986), a physical model was used to derive design criteria for the system of transverse bar structures (Fig. 2). Figure 2 shows from left 2 transverse bar structures with the upstream channel and 4 transverse bars.