Ramp Larsenwehr and Widening / Drau, Assling

Project objectives

The project aimed to modify the Larsenwehr on the Drau in Assling to restore fish passability, improve the river’s morphological conditions, and enhance flood protection. Planned measures included converting the weir into a fish-passable ramp and widening the Drau.

Project description

The Larsenwehr, constructed in 1932 to stabilise the riverbed, represented a migration barrier for fish. Core measures: conversion of the Larsenwehr into a 170 m long, 2.5 % sloped bed ramp with deep channels and short groynes; widening of the Drau over 210 m to a bed width of up to 16 m with flatter banks (1:2–1:6), structural groynes and deep channels; relocation of the right-bank cycle path over 300 m; creation of a biotope and a 225 m long side arm as a refuge for fish.

Project data

• Study area: Drau river kilometres 643.00 - 642.10
• Total length of the measures: approx. 900 m
• Slope of the riverbed ramp: 2.5 %

Services

Hydraulic 2D modelling, provision of flood protection for HQ₁₀₀ with 1.00 m freeboard, planning of fish-ecological measures, stability verifications, preparation of technical reports and planning documents, and coordination with authorities for water, forestry and nature conservation permits.