Rainfall-Runoff-Inundation (RRI) Model

     1. Model Structure Overview

Rainfall-Runoff-Inundation (RRI) model is a two-dimensional model capable of simulating rainfall-runoff and flood inundation simultaneously (Sayama et al., 2012, Sayama et al., 2015). The model deals with slopes and river channels separately. At a grid cell in which a river channel is located, the model assumes that both slope and river are positioned within the same grid cell. The channel is discretized as a single line along its centerline of the overlying slope grid cell. The flow on the slope grid cells is calculated with the 2D diffusive wave model, while the channel flow is calculated with the 1D diffusive wave model. For better representations of rainfall-runoff-inundation processes, the RRI model simulates also lateral subsurface flow, vertical infiltration flow and surface flow. The lateral subsurface flow, which is typically more important in mountainous regions, is treated in terms of the discharge-hydraulic gradient relationship, which takes into account both saturated subsurface and surface flows. On the other hand, the vertical infiltration flow is estimated by using the Green-Ampt model. The flow interaction between the river channel and slope is estimated based on different overflowing formulae, depending on water-level and levee-height conditions.

Schematic diagram of Rainfall-Runoff-Inundation (RRI) Model (Sayama et al., 2012)

2. Model Features

1) RRI is a 2D model simulating for rainfall-runoff and flood inundation simultaneously.

2) It simulates flows on land and in river and their interactions at a river basin scale.

3) It simulates lateral subsurface flow in mountainous areas and infiltration in flat areas.

RRI Model is free downloadable from ICHARM website in this link http://www.icharm.pwri.go.jp/research/rri/rri_top.html

Application of RRI Model in the Mekong River Basin (Try et al., 2018, 2020)

References

Sayama, T., G. Ozawa, T. Kawakami, S. Nabesaka and K. Fukami (2012). "Rainfall–runoff–inundation analysis of the 2010 Pakistan flood in the Kabul River basin." Hydrological Sciences Journal 57(2): 298-312.

Sophal, T., L. Giha, Y. Wansik, O. Chantha and J. Changlae (2018). "Large-scale Flood Inundation Modeling in the Mekong River Basin." Journal of Hydrologic Engineering. DOI: 10.1061/(ASCE)HE.1943-5584.0001664.

Try S., Tanaka S., Tanaka K., Sayama T., Lee G., Oeurng C. (2020). Assessing the effects of climate change on flood inundation in the Lower Mekong Basin using high-resolution AGCM outputs. Progress in Earth and Planetary Science. doi: 10.1186/s40645-020-00353-z.

Try S., Tanaka S., Tanaka K., Sayama T., Hu M., Sok T., Oeurng C. (2020). Projection of extreme flood inundation in the Mekong River Basin under 4 K increasing scenario using large ensemble climate data. Hydrological Processes. doi: 10.1002/hyp.13859.

Try S., Tanaka S., Tanaka K., Sayama T., Oeurng C., et al. (2020). Comparison of gridded precipitation datasets for rainfall-runoff and inundation modeling in the Mekong River Basin. PloS One, 15(1),e0226814.

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