Abstract
Although river discharge is essential hydrologic information, it is often absent, especially for small rivers and remote catchment areas. Practical difficulties frequently impede the installation and operation of gauging stations, while satellite-sensed data have proved to be relatively useful only for discharge estimation of large-scale rivers. In this study, we propose a new methodology based on UAV-sensed data and photogrammetry techniques combined with empirical hydraulic equations for discharge estimation. In addition, two different riverbed particle size distributions were incorporated, to study the effect of fine sediment inclusion (or exclusion) in the estimation process. Accordingly, 17 study sites were selected and six different approaches were applied in each. Results show that at 75% of sites at least one approach produced an accurate discharge estimation, while in 10 out the 17 sites (58.8%) all six approaches produced accurate estimations. A strong correlation between a threshold value for the hydraulic radius (Rh = 0.3 m) of cross-sections and high estimation errors for sites exceeding it was also observed. The fine sediment inclusion improved only the performance of certain approaches and did not have a consistently positive effect. Overall, the relatively high percentage of sites with satisfactory discharge estimates indicates that using UAV-derived data and simple hydraulic equations can be used for this purpose, with an acceptable level of accuracy.
Highlights
IntroductionMeasurements of discharge are often absent as conventional gauging methods are expensive and impractical as well as hard to deploy and maintain [3,4]
The aim of this study is to identify the optimal methodological approach for river discharge estimation, by combining UAV produced Digital Surface Models (DSM), orthophotomaps and classical hydraulic equations (Manning)
Using UAV products and photogrammetric approaches to estimate discharge in shallow rivers can provide an efficient solution for monitoring ungauged and difficult to access rivers, with an affordable and reliable methodology
Summary
Measurements of discharge are often absent as conventional gauging methods are expensive and impractical as well as hard to deploy and maintain [3,4]. These limitations are true for water bodies located in remote locations, for rivers and streams with ephemeral flow and for small catchment areas. This is of great concern, since the latter are impacted from flash floods, one of the most significant natural hazards, known to cause serious loss of life and economic damage [5], especially in Mediterranean regions [6]
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