Computation of Hydro-geomorphologic Changes in Two Basins of Northeastern Greece

This chapter presents a composite mathematical model aiming at continuous simulations of hydro-geomorphological processes at the basin scale. Continuous hydrologic simulations, as well as continuous simulations of soil and streambed erosion processes, are performed in two neighbouring basins in northeastern Greece: Kosynthos river basin (district of Xanthi, Thrace, northeastern Greece) and Nestos river basin (Macedonia-Thrace border, northeastern Greece). Both basins are mountainous and covered by forested and bushy areas in their greatest part. Kosynthos river basin extends to an area of 237 km2, whilst Nestos river basin is quite bigger, covering an area of approximately 840 km2. The characteristic of Nestos river basin is the presence of a dam at its northwestern boundary, which largely affects the discharge, as well as the sediment transport in Nestos River. The application of the model results in continuous hydrographs and sediment graphs at the outlets of the two basins. Fine temporal scales are used, providing this way a continuous assessment of water and sediment discharge. The statistic efficiency criteria utilized for the comparison between computed and measured values of water and sediment discharge at the basin outlet provide satisfactory results. Therefore, it is concluded that the continuous hydro-geomorphologic modelling can be successfully applied to Kosynthos and Nestos river basins

Ανάπτυξη μαθηματικού ομοιώματος για τον υπολογισμό συνεχών υδρογραφημάτων και στερεογραφημάτων σε μια λεκάνη απορροής λόγω βροχόπτωσης

In this thesis, three different models aiming at continuous simulations of hydromorphological processes at the basin scale, are presented. More specifically, continuous hydrologic simulations, as well as continuous simulations of soil and streambed erosion processes are performed in two neighboring basins in northeastern Greece: Kosynthos River basin (district of Xanthi, Thrace, northeastern Greece) and Nestos River basin (Macedonia-Thrace border, northeastern Greece). Both basins are mountainous and covered by forested and bushy areas in their greatest part. Kosynthos River basin extends to an area of 237 km2, whilst Nestos River basin is quite bigger, covering an area of approximately 840 km2. The characteristic of Nestos River basin is the presence of a dam at its northwestern boundary, which largely affects the discharge, as well as the sediment transport in Nestos River. Along with this, two irrigation canals slightly upstream of the basin outlet (Egnatia bridge of Nestos River) are culpable of a recession of water, during the irrigation period, disrupting the final discharge at the basin outlet. The two first models are two Composite Mathematical Models (CMMs), which were developed by combining several known physically-based and empirical methods together. The CMMs consist of three submodels: a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. The two models only differ in the soil erosion submodel. The rainfall-runoff submodel that is used for the computation of the surface runoff and the streamflow in the sub-basins, is the deterministic semi-distributed hydrologic model HEC-HMS 4.2. The first soil erosion submodel, utilized for the estimation of soil erosion in a sub-basin, is based on the relationships of Poesen (1985), Nielsen (1986), Engelund and Hansen (1967), while the second is the widely known Modified Universal Soil Loss Equation (MUSLE). The estimation of sediment yield at the outlet of a sub-basin, and finally at the outlet of the whole basin, is achieved by means of the stream sediment transport model of Yang and Stall (1976). The third model is the GIS version of the, well known, Soil and Water Assessment Tool, SWAT. SWAT is applied in its finest temporal scale available (30-minute time step simulations), whilst the application of the two Composite Mathematical Models (CMMs) is performed at an hourly time step. The application of all three models results to continuous hydrographs and sediment graphs at the basin outlet. The computed stream discharge and sediment discharge values are compared with field measurements and all models are evaluated as to their competence of simulating the hydromorphological processes in a basin. Annual water and sediment yields are also computed for the two basins. The statistic efficiency criteria utilized for the comparison between computed and measured values at the basin outlet, provide satisfactory results. Therefore, it is concluded that the continuous hydromorphologic modeling can be successfully applied to Kosynthos and Nestos River basin.Σε αυτή τη διδακτορική διατριβή παρουσιάζονται τρία διαφορετικά μοντέλα με στόχο τις συνεχείς προσομοιώσεις των υδρομορφολογικών διεργασιών σε επίπεδο λεκάνης απορροής. Πιο συγκεκριμένα, εκτελούνται συνεχείς υδρολογικές προσομοιώσεις, καθώς και συνεχείς προσομοιώσεις των διεργασιών εδαφικής διάβρωσης και διάβρωσης κοίτης υδατορευμάτων σε δύο γειτονικές λεκάνες στη βορειοανατολική Ελλάδα: στη λεκάνη απορροής του ποταμού Κόσυνθου (περιοχή Ξάνθης) και στη λεκάνη απορροής του ποταμού Νέστου (σύνορα Μακεδονίας-Θράκης). Και οι δύο λεκάνες είναι ορεινές και καλύπτονται από δασικές και θαμνώδεις περιοχές, στο μεγαλύτερο τους μέρος. Η λεκάνη απορροής του ποταμού Κόσυνθου καλύπτει μια έκταση 237 km2, ενώ η λεκάνη απορροής του ποταμού Νέστου είναι αρκετά μεγαλύτερη, καλύπτοντας μια έκταση περίπου 840 km2. Το χαρακτηριστικό της λεκάνης του ποταμού Νέστου είναι η παρουσία ενός φράγματος στο βορειοδυτικό όριό της, το οποίο επηρεάζει σε μεγάλο βαθμό την παροχή, καθώς και τη μεταφορά φερτών υλών στον ποταμό Νέστο. Επιπρόσθετα, δύο αρδευτικά κανάλια πολύ κοντά στην έξοδο της λεκάνης (γέφυρα Εγνατίας του ποταμού Νέστου) ευθύνονται για μια ύφεση στην παροχή του ποταμού, κατά τη διάρκεια της αρδευτικής περιόδου, διαταράσσοντας έτσι την τελική απορροή στην έξοδο της λεκάνης. Τα δύο πρώτα μοντέλα είναι δύο σύνθετα μαθηματικά μοντέλα (Composite Mathematical Models/CMMs), τα οποία αναπτύχθηκαν συνδυάζοντας διάφορες γνωστές φυσικές και εμπειρικές μεθόδους. Τα σύνθετα μαθηματικά μοντέλα αποτελούνται από τρία υπομοντέλα: ένα υπομοντέλο βροχής-απορροής, ένα υπομοντέλο εδαφικής διάβρωσης και ένα υπομοντέλο στερεομεταφοράς για υδατορεύματα. Τα δύο μοντέλα διαφέρουν μόνο στο υπομοντέλο εδαφικής διάβρωσης. Το υπομοντέλο βροχής-απορροής που χρησιμοποιείται για τον υπολογισμό της επιφανειακής απορροής και της απορροής των υδατορευμάτων στις υπολεκάνες, είναι το ντετερμινιστικό, ημι-κατανεμημένο, υδρολογικό μοντέλο HEC-HMS 4.2. Το πρώτο υπομοντέλο εδαφικής διάβρωσης, που χρησιμοποιείται για την εκτίμηση της διάβρωσης του εδάφους σε μια υπολεκάνη, βασίζεται στις σχέσεις των Poesen (1985), Nielsen (1986), Engelund και Hansen (1967), ενώ το δεύτερο είναι η Τροποποιημένη Παγκόσμια Εξίσωση Απωλειών Εδάφους (MUSLE) (Williams, 1975). Η εκτίμηση του στερεοφορτίου στην έξοδο μιας υπολεκάνης, και τελικά, στην έξοδο της όλης λεκάνης, επιτυγχάνεται με τη βοήθεια του μοντέλου μεταφοράς φερτών υλών των Yang και Stall (1976). Το τρίτο μοντέλο είναι η GIS έκδοση του ευρέως γνωστού μοντέλου Soil and Water Assessment Tool, SWAT. Το SWAT εφαρμόζεται στη μικρότερη χρονική κλίμακα που διαθέτει (ημίωρο χρονικό βήμα προσομοίωσης), ενώ η εφαρμογή των δύο σύνθετων μαθηματικών μοντέλων εκτελείται σε ωριαίο χρονικό βήμα. Η εφαρμογή και των τριών μοντέλων έχει ως αποτέλεσμα την κατασκευή συνεχών υδρογραφημάτων και στερεογραφημάτων στην έξοδο της λεκάνης. Οι υπολογισμένες τιμές παροχής και στερεοπαροχής συγκρίνονται με μετρήσεις πεδίου και όλα τα μοντέλα αξιολογούνται ως προς την ικανότητά τους να προσομοιώνουν τις υδρομορφολογικές διεργασίες σε επίπεδο λεκάνης απορροής. Επίσης, ετήσιοι όγκοι νερού και ετήσια στερεοφορτία υπολογίζονται για τις δύο λεκάνες. Τα στατιστικά κριτήρια απόδοσης που χρησιμοποιούνται για τη σύγκριση μεταξύ υπολογισμένων και μετρημένων τιμών στην έξοδο της λεκάνης, παρέχουν ικανοποιητικά αποτελέσματα. Ως εκ τούτου, συνάγεται το συμπέρασμα ότι η συνεχής υδρομορφολογική μοντελοποίηση μπορεί να εφαρμοστεί με επιτυχία στη λεκάνη απορροής του ποταμού Κόσυνθου και στη λεκάνη απορροής του ποταμού Νέστου

Soil Erosion, Streambed Deposition and Streambed Erosion—Assessment at the Mountainous Terrain

An Integrated Mathematical Model (IMM) is applied at a continuous time scale in Nestos River basin (Macedonia–Thrace border, northeastern Greece). The IMM comprises a rainfall–runoff submodel, a soil erosion submodel, a streambed deposition submodel and a streambed erosion submodel, and computes sediment yields at the outlet of the basin, at fine time steps and for long periods of time. Soil erosion is estimated by means of the Modified Universal Soil Loss Equation (MUSLE), deposition of sediment load is modeled by the formulas of Einstein and Pemberton and Lara, while streambed erosion is estimated through the formula of Smart and Jaeggi. The application of the IMM enables the computation of annual sediment yields, at the outlet of the basin

Comparison between Calculation and Measurement of Total Sediment Load: Application to Streams of NE Greece

Sediment transport and stream discharge are two of the natural procedures which affect the hydromorphological profile of a watercourse. Measurements of water discharge, bed load transport rate and suspended sediment concentration were conducted in Kosynthos River and Kimmeria Torrent –two intermittent streams– in north-eastern Greece. The total sediment concentration was calculated, in both streams, by means of various nonlinear regression equations and by means of the formulas of Yang, after calibrating the coefficients of the formulas. In the computations according to the Yang formulas, two different states were examined regarding the incipient motion: one considering and one disregarding the critical conditions. The results obtained from Yang’s multiple regression-derived equations had a better fit compared to the original equations and were acceptable in both cases. Ultimately, two counterparts of Yang’s stream sediment transport formulas were constructed and made available to the readership. The comparison between the calculated and measured total sediment concentrations was achieved by means of several statistical criteria. The results indicate that the modified formulas of Yang can be successfully used for the determination of the total sediment concentration in Kosynthos River and Kimmeria Torrent

Assessing the Impact of Man–Made Ponds on Soil Erosion and Sediment Transport in Limnological Basins

The impact of ponds on basins has recently started to receive its well-deserved scientific attention. In this study, pond-induced impacts on soil erosion and sediment transport were investigated at the scale of the French Claise basin. In order to determine erosion and sediment transport patterns of the Claise, the Coordination of Information on the Environment (CORINE) erosion and Soil and Water Assessment Tool (SWAT) models were used. The impact of ponds on the studied processes was revealed by means of land cover change scenarios, using ponded versus pondless inputs. Results show that under current conditions (pond presence), 12.48% of the basin corresponds to no-erosion risk zones (attributed to the dense pond network), while 65.66% corresponds to low-erosion risk, 21.68% to moderate-erosion risk, and only 0.18% to high-erosion risk zones. The SWAT model revealed that ponded sub-basins correspond to low sediment yields areas, in contrast to the pondless sub-basins, which yield appreciably higher erosion rates. Under the alternative pondless scenario, erosion risks shifted to 1.12%, 0.52%, 76.8%, and 21.56% for no, low, moderate, and high-erosion risks, respectively, while the sediment transport pattern completely shifted to higher sediment yield zones. This approach solidifies ponds as powerful human-induced modifications to hydro/sedimentary processes

The effects of a sediment flushing on Alpine macroinvertebrate communities

Sediment flushing from dams can help desilting reservoirs and reinstate the longitudinal sediment transfer continuity in rivers, but negative ecological impacts might arise. We monitored the ecological effects of a flushing event conducted from 27th May to 14th June 2019 in the Rienz River, in South Tyrol (NE Italy). Using a multi-habitat scheme approach, we collected macroinvertebrates 10 days before, and then 40 and 74 days after the completion of the operations. We selected seven biological traits—organism size, life cycle duration, mobility (dispersal and locomotion), feeding type, substrate and current velocity preference—to characterize and compare the invertebrate communities before and after the sediment pulse disturbance. Turbidity was recorded continuously for the entire duration of the event. Results indicate that invertebrate assemblages exhibited a general decrease in taxonomic richness and Shannon diversity 40 days after the event, but density and richness recovered over time. Shifts in species composition were observed in post flushing samples, with a reduction in density of sensitive species (Heptageniidae) and shredders. Post-flushing samples were generally characterized by sediment-tolerant taxa, able to cope with the new habitat conditions. Altered taxonomic and functional community composition following the flushing prevented the full functional recovery to pre-disturbance condition

Understanding the cost of soil erosion: An assessment of the sediment removal costs from the reservoirs of the European Union

International audienceSoil erosion is both a major driver and consequence of land degradation with significant on-site and off-site costs which are critical to understand and quantify. One major cost of soil erosion originates from the sediments delivered to aquatic systems (e.g., rivers, lakes, and seas), which may generate a broad array of environmental and economic impacts. As part of the EU Soil Observatory (EUSO) working group on soil erosion, we provide a comprehensive assessment of the existing costs of sediment removal from European Union (EU) catchments due to water erosion. These quantifications combine continental average and regionally explicit sediment accumulation rates with published remediation costs, integrating numerous figures reported in the grey literature. The cost of removing an estimated 135 million m 3 of accumulated sediments due to water erosion only is likely exceeding 2.3 billion euro (€) annually in the EU and UK, with large regional differences between countries. Considering the sediment delivered through all soil loss processes (gullies, landslides, quarrying, among others) through extrapolating measured reservoir capacity losses, the sediment accumulation in the circa 5000 EU large reservoirs exceeds 1 billion m 3 with a potential cost of removal ranging between 5 and 8 billion € annually. These estimates, although not accounting for already implemented catchment mitigation measures, provide insights into one of the off-site costs of soil erosion at both the continental scale as well as the regional differences in economic burden. The provided estimates contribute to support policies such as the Soil Monitoring Law, the Zero Pollution Action Plan, the Farm to Fork strategy and the Water Framework Directive