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Agricultural University of Athens (2016)

Development of strategies for the quantitative assessment of sediment yield by water erosion using decision support systems at mountainous catchments

Efthimiou, Nikolaos of Georgios

Titre : Development of strategies for the quantitative assessment of sediment yield by water erosion using decision support systems at mountainous catchments

Auteur : Efthimiou, Nikolaos of Georgios

Etablissement de soutenance : Agricultural University of Athens

Grade : Doctor of Philosophy (PhD) 2016

Résumé
Τhe main objective of this PhD dissertation was the improvement of soil loss estimation at mountainous Mediterranean type catchments, as well as the identification of the most susceptible to erosion areas.Study area included the catchments of Venetikos (Grevena Bridge sub-catchment), Kalamas (Soulopoulo Bridge and Kioteki sub-catchments) Arachthos (Arta ; Plaka ; Tsimovo ; Gogo Bridge sub-catchments) and Acheloos (Avlaki Dam sub-catchment) Rivers.The methodology followed was initially comprised by the implementation of twelve different empirical soil erosion models at each sub-catchment, both annually and inter-annually. Subsequently, the models’ performance was evaluated qualitatively (as far as their specific characteristics and capabilities is concerned) and quantitatively [their numeric results were cross-evaluated with the sub-catchment’s measured sediment yield (PPC)], in order to select the one corresponding best to the region’s specific conditions. The prevalent one (RUSLE), taking under consideration its annual numeric results as long as the corresponding measured sediment yield ones, was modified (its individual factors were assigned with a weighing coefficient) using statistical procedures, in order to improve its predicting ability minimizing the numeric value of the Σ(SYsim-SYobs)2 error term, between observed and simulated results. Concerning the modification process, the sediment yield values estimated by the corresponding sediment discharge measurements (PPC) were initially considered as measured. Their questionable reliability along with their lack at the Kalamas River sub-catchments, led to their replacement by the ones calculated by the representative suspended sediment discharge rating curve construction method of each sub-catchment. All models were anew cross-evaluated considering the new dataset, with the RUSLE remaining prevalent. The estimated error term Σ(SYsim-SYobs)2 was gradually reduced from 40,213.06t/ha (no weighing coefficients) to 25,937.07t/ha (weighing coefficients attributed considering the PPC results) to 5,834.78t/ha (weighing coefficients attributed considering the rating curve methods results/ selected equation).The selected equation was anew implemented to all sub-catchments at both time scales. The results were compared to the ones attributed by the original equation, as well as the simulated sediment yield values (based on the sediment discharge rating curve methods), in order to evaluate its performance and credibility. The model performed exceptionally well at some sub-catchments (Kioteki, Soulopoulo Bridge, Gogo Bridge), while not so well at others (Venetikos River, Plaka Bridge). At the remaining sub-catchments there was a slight predominance of the original equation (more vague annually), but there is no marked differentiation leading effortlessly to the rejection of the methodology.This irregular behavior was mainly attributed to the relatively small dataset taken into account in order to determine the weighing coefficient of each factor, their specific characteristics (hydrological regime, climate, soil types, morphology, soil cover) as well as other extrinsic elements (model implementation errors, field measurements errors, shortcomings in measurement methodologies and model’s construction).

Mots clés : Soil erosion ; Erosion models ; Sediment discharge ; Sediment yield ; Northwestern Greece ; Venetikos ; Kalamas ; Acheloos ; Arachthos ; Revised universal soil loss equation

Présentation (National Archives PhD)

Page publiée le 15 novembre 2022