Spatial lumping of a distributed rainfall‐sediment‐runoff model and its effective lumping scale

Abstract

Abstract:This paper proposes a method to spatially lump a distributed rainfall-sediment-runoff model at the catchment scale. Based on a kinematic wave rainfall-sediment-runoff model, the proposed method spatially integrates (1) a rainfall-runoff model that simulates unsaturated, saturated subsurface and surface runoff processes and (2) a rainfall-sediment-runoff model that simulates soil erosion and transport processes induced by raindrops and surface flow detachment, respectively. The method deductively derives a set of lumped equations that relates the streamflow discharge and the catchment storage of water and sediment, which are then used together with continuity equations to predict the sediment runoff fluxes from the catchment outlet. The main advantage of the method is that the derived lumped model parameters are reflected by the spatially distributed topographical and soil property information, and yet the model can be implemented with a much less computational load compared to the original distributed model. Thus, the model gives a possibility of its numerous applications À such as the application to real-time flood forecasting, sediment yield-flood prediction for hydraulical structure designing, and for a climate change impact analysis on hydrological responses À coupled with the risk and uncertainty analyses which require a number of simulations. The developed lumped model successfully simulated the original distributed model outputs, as well as the observed streamflow and sediment at the Lesti River Catchment (381 km 2 ), a tributary of the Brantas River Basin in Indonesia. After validating the proposed lumped model, the most effective lumping scale was then investigated by conducting multiple simulations, the results of which suggested that approximately 200 km 2 is the ideal lumping scale for this model.

When does higher spatial resolution rainfall information improve streamflow simulation? An evaluation using 3620 flood events

“…These results allow us to generalize, with confidence, the conclusions drawn by previous studies (but only obtained over a few catchments) that reported a lack of significant differences between lumped and semidistributed flow simulations at the catchment outlet (Ajami et al, 2004;Apip et al, 2012;Bell and Moore, 2000;Lindström et al, 1997;Naden, 1992;Nicòtina et al, 2008;Obled et al, 1994;Refsgaard and Knudsen, 1996). However, we found that the impact of higher resolution in precipitation inputs were catchment-dependent since the quality of streamflow simulations was significantly improved at the outlet of catchments exposed to high rainfall intensity, and these improvements rose with catchment area.…”

“…Other studies have tested different modeling configurations, from lumped to (semi-) distributed, in order to investigate the impact of spatial precipitation inputs on streamflow simulations. Many of them reported that increased resolution in space had little effect on the model's performance and that distributed modeling approaches may not always provide improved outlet simulations compared to lumped approaches (Ajami et al, 2004;Apip et al, 2012;Bell and Moore, 2000;Das et al, 2008;Lindström et al, 1997;Liu et al, 2012;Naden, 1992;Nicòtina et al, 2008;Obled et al, 1994;Reed et al, 2004;Refsgaard and Knudsen, 1996;.…”

Modeling of extreme freshwater outflow from the north-eastern Japanese river basins to western Pacific Ocean

“…(Sasaki, 2014;Luo et al, 2014;Apip et al, 2011;Sayama and McDonell, 2009;Tachikawa et al, 2004;Sayama et al, 2003, Kojima et al, 1998 for simulating river discharge, depending upon basin properties and rainfall. We simulated total freshwater outflow at river mouths from all of the nine first class river basins flowing from the north- For two rivers (Takase and Tone) the simulation was not made at the river mouth but on the most downstream available discharge stations Ueno and Nunokawa (afterwards renamed to Fukawa) respectively, because we did not have any discharge data available close to the river mouth.…”

Ensemble flood simulation for a small dam catchment in Japan using 10 and 2 km resolution nonhydrostatic model rainfalls

“…The DRR model applied is that originally developed by Kojima and Takara (2003) called CDRMV3. The details of this DRR model can be seen in the work by Apip et al (2011). In the DRR model, the surface and river flows are simulated using a 1-D kinematic wave model.…”