Floodplain inundation studies

Floods caused by the sudden flooding of rivers during periods of intense rainfall are the most frequent danger and cause the most material and human damage .

Flood risk studies bring together different disciplines, including surface hydrology and fluvial dynamics typically addressed by geologists and biologists, canal hydraulics worked from civil engineering, geomatic techniques for three-dimensional terrain characterization, and numerical methods for the iterative resolution of the flow problem in channels. In this sense, to carry out a flood risk study, the following tasks are carried out:

1. First of all, it is necessary to collect as much background information as possible about the study area, such as data from rainfall records, records of drafts reached in important events, and everything that may refer to the hydraulic and hydrological behavior of the basin.
2. It is necessary to carry out some field visits to carry out all types of observations, from roughness coefficients, geometries and critical points to evaluations of paleofloods.
3. A three-dimensional model of the terrain is made with a topography at a scale of 1: 1000 or 1: 2000 with higher resolution in the critical sections and all those that dominantly control the flow, such as viaducts, channels, canalizations, deviations, incorporations, etc…
4. A conceptual hydrological model of the basin is made , with the collected data and the terrain model. The HEC-HMS program is used to create a hydrological model with which the rainfall data that has previously been treated statistically is transformed into flow hydrographs associated with return differences.
5. A hydraulic model of the river or rivers and canals involved in the study is made using the HEC-RAS program, thereby creating a geometric model based on the characterization of the terrain and the geometry of the rivers and canals with which They impose the hydraulic conditions obtained from the hydrological model of the basin carried out with HEC-HMS. In this hydraulic model, the different scenarios are characterized, the natural state, the state with the current anthropic intervention, the scenario with the new intervention to be carried out and the scenario with the possible corrective measures.
6. Once these tasks were completed, a synthesis report was carried out with all the relevant information of the study, the hypotheses made, the data used and the results obtained, as well as the conclusions and the definition of the necessary measures to reduce the danger against episodes of channel overflow.
7. Additionally, a vulnerability study can be carried out on the structures and facilities that may be affected by floods. Once the danger is known, the result of the flood risk study and characterized by flow rates, drafts and flow speeds, the risk associated with flooding can be evaluated, probabilistically, as the product of the danger, the vulnerability and the exposure of the elements susceptible to be harmed by this risk.

One of the main objectives of flood studies is to characterize the hydrological behavior of the basin with the corresponding hydrographs for different return periods, as well as the hydraulic behavior of the natural drainage network and channeling, obtaining the flow rates, drafts, flow velocities and with special attention to the flood plains for the different return periods considered.

The cost ranges are highly variable depending on the characteristics of each study, where the number of rivers to model and the extent of the study area can largely determine the final magnitude of the costs.