Improving river routing algorithms to efficiently implement canal water diversion schemes in global hydrological models

Abstract

In global hydrological models, river discharge is accumulated by following the river network, which presumes that there is one downstream destination for each grid. Implementing “diversions” where there are multiple downstream destinations, such as bifurcations and inter-basin water transfers, requires an extension of river routing algorithms. Previous global water resources models that implemented diversions typically used a semi-implicit numerical scheme where river discharge should be calculated in an upstream-to-downstream order. The major obstacle to flexible application to any river network with diversions was that ad-hoc modification of the model’s code was required because the river sequence map to specify calculation order was developed without considering diversions. To overcome this limitation, we developed two new river routing algorithms that can generally represent diversions. One is automatically updating river sequence considering diversions and the other is introducing the Forward Time Centered Space scheme. The former has the advantage of stability under longer time steps, while the latter’s strength lies in its easy implementation and applicability where backwater happens. We confirmed that both algorithms efficiently handle the complex canal network in the Indus River. These approaches allow us to flexibly implement diversions in river routing algorithms.