Gensen, Matthijs R.A.

Hulscher, Suzanne J.M.H.

Huthoff, Fredrik

Warmink, Jord Jurriaan

The amount of discharge in a river section is a key uncertainty factor in flood risk analyses and is determinedby upstream conditions as well as the distribution of discharge over river branches at river bifurcations. Thisstudy assesses the impact of river interventions in a bifurcating river system, considering the Dutch river Rhinesystem with its two bifurcation points. The river system is schematized in a 1D model, using the main channel roughness and floodplain roughness as stochastic variables. With this model we evaluated the uncertainimpact of river interventions with varying locations and dimensions. Model results show self-regulation ofdownstream water levels and water level uncertainties through changes in the discharge distribution at bifurcation points. This is explained by a self-regulating mechanism in which the water level lowering impact of anriver intervention induces an increase in discharge towards the branch in which the river intervention was implemented. This effectively reduces the impact of the intervention. Additionally, the self-regulating mechanismreduces the uncertainty of the impact of the river intervention. So, compared to a non-bifurcating river system,the impact of river interventions on flood water levels reduces, but involves less uncertainty. Furthermore, results show that the self-regulating mechanism has a larger influence in the smaller distributaries compared tothe larger distributaries. Considering the results, it is essential to regard the entire river system, and specificallythe influence on the distribution of discharge at bifurcation points, in the design and assessment of river interventions. We conclude that in a bifurcating river system, water levels and their uncertainties are controlled bya self-regulating mechanism. Water level uncertainties are smaller and therefore, flood risk estimates are morecertain if considering this self-regulating mechanism in flood risk analyses

Self-regulation of flood water levels for the uncertain impact ofriver interventions in a bifurcating river system

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