Flood Modeling Using Conventional Land Surveys, Digital Mapping and Drone Survey

The hydraulic modeling of flooding preferably implies having detailed ground-based survey information (topo-bathymetry), which requires arduous field work, time, a substantial budget.

Digital cartography and land surveys using drones may also offer interesting information to represent the river domain but they are associated with much less time, risk, and cost. The purpose of this work was to compare flood areas using three different digital elevation models (DEM). These models were constructed in previous studies from digital mapping and common ground-based surveys for more than 20 km in the rivers Molino, Cauca and Ejido in Popayán, located in in Southwestern Colombia. Drones were also used to represent the river domain in the most flood-prone zones.

The region lacks enough economic resources to undergo extensive field work or detailed Lidar information, so alternatives had to be found to produce the hazard flooding maps for purposes of land use planning.

The research clarifies the difficulties and conveniences of three different DEM to model floods in areas with scarce information, low budget and numerous social conflicts. Unfortunately, it is not possible to use the results for planning purposes, since the research did not involve the anthropogenic actions that alter rivers such as bridges and calibration was not done.

Some of the results show that use of drones is promising to replace conventional land surveys only in the case of riverbanks clear of vegetation, but with a substantial reduction in costs and risks.

The drone serves to speed up field work, but, it is always expedient to also use common ground-based survey to characterize the river banks in areas where there is vegetation in order to obtain more accurate river profiles and cross sections.

Unless we have excellent data, digital mapping can be used in preliminary studies as an approximation of the flooding areas while reducing the cost of the studies when compared to conventional land surveys.

The length of the reach is the shortest when taken with the drone model with respect to the other two DEMs. Hydraulic parameters such as maximum water depth, average velocity, top width, and Froude Number are in between the values obtained with the topography and the digital cartography models. The top width is always the smallest and the maximum water depth, average velocity and Froude number are always the highest when the topo-bathymetric DEM is used.

KEY WORDS: floods, hydraulic modeling, rivers, Digital Elevation Model (DEM), land survey