Hydrogeomorphological approaches to understand flood hazards and flood-risks management in NW Rwanda
Date: 2020 - 2024
Chercheur impliqué: Deogratias NAHAYO, doctorant
1. Research question
Nowadays, a good number of numerical approaches have been developed to estimate design floods. The availability of faster computers has made it possible to apply such advanced flood modeling techniques using numerical solutions to the flow equations of the river engineering subject. Simultaneously, recent techniques allow for rapidly collecting the high-quality input data for these models with remotely sensed data such as digital elevation models (DEM) with light detection and ranging/laser imaging detection and ranging (LIDAR) techniques, LULC maps of high-resolution satellite images. These techniques have made it possible to simulate flood behaviors and predict the extent of future flood events. This is a good achievement in hydrological assessments because it offers opportunities to rapidly determine the design floods but it is also a trigger as the field-based data are the most important to accurately estimate the design floods and predict the extent of flood hazards and flood risks for the future. In addition, estimation of the design flood or peak discharge or probable maximum flood deals with determining the volume and period that it should occur to facilitate the design. Thus, there is a need of analyzing the causative factors responsible for the generation of such floods to arrive at the most critical combination of hydrologic (e.g. heavy rains), geologic (e.g. soil types), morphometric (e.g. relief/river slopes, basin shapes, river topology, etc.), and anthropogenic (e.g. land use, poor design, poor management of hydraulic structures, etc.) factors.
From the above- issues come up with the following research question:
Is it possible to find with good accuracy the main factors influencing rainfall-runoff response by the extent of occurrence of flood events in relation to the topography, soil types, and LULC based on short-term field observations, the statistical and numerical approaches?
2. Research objectives
The overall objective of this research is “to demonstrate that it is possible to find, with good accuracy, the main factors influencing Rainfall-Runoff (RR) response by the extent of occurrence of flood events in relation to the topography, soil characteristics, and LULC, based on representative sub-catchments taken as sites of monitoring, in Mukungwa and Sebeya watersheds ”. This main objective will address the following specific objectives:
- To analyze the main factors influencing rainfall-runoff response regarding flood events;
- To provide detailed and reliable short-term RR observations by a set of eight representative sub-catchments with contrasting soil types, topographies, and LULC conditions;
- To develop tools that can help in better understanding flood hazards and flood risks, and better design flood management projects, based on RR relation, LULC, soil types, and other potentially relevant factors;
- To estimate the probable maximum floods that can cause serious threats to lives, properties, and hydraulic infrastructure].
3. Research hypotheses
To achieve the above specific objectives, the following hypotheses have been drawn:
- LULC change can cause higher surface runoff and lower or higher infiltration rates in steeped areas.
- Soil characteristics have an important role in attenuating or accelerating runoff generated by heavy rains in steeped areas.
- LULC, topography, and soil characteristics significantly influence the rainfall-runoff response by the extent of the occurrence of flood events but at different magnitudes.
