A measurement campaign was carried out in the Upper Tana basin (Kenya) to quantify soil erosion and reservoir sedimentation rates, including a bathymetric reservoir survey and sediment load sampling during one year. Then, distributed soil erosion modelling was performed to study sediment budgets throughout the basin and to evaluate the potential of upstream erosion control through vegetated contour strips and check dams. Finally, the areas where these measures would be most effective were identified and local stakeholder associations to implement them were prioritized. The influence of the scale of implementation was evaluated by using the model to consider three adoption scenarios. This study illustrates the relevance of distributed erosion models to target erosion control measures when sufficient information on the eroding areas is available from field surveys. Bathymetric surveys were fundamental to validate the long-term model response, while point measurements were valuable to verify the spatial variability of model predictions.Key words soil erosion; sediment yield; sedimentation rate; distributed model; SWAT; Kenya; erosion control; soil conservation; watershed management Détermination des zones d'intervention pour la réduction de la sédimentation des réservoirs du bassin du Tana (Kenya) en utilisant SWAT Résumé Une campagne de mesures a été réalisée dans le bassin du Haut Tana (Kenya) afin de quantifier l'érosion des sols et les taux de sédimentation dans le réservoir, comprenant une étude bathymétrique du réservoir et l'échantillonnage des sédiments déposés pendant un an. Une modélisation distribuée de l'érosion des sols a ensuite été réalisée pour étudier le bilan des sédiments dans le bassin et évaluer le potentiel de contrôle de l'érosion en amont, par des bandes de végétation suivant les courbes de niveau et des barrages de retenue. Nous avons enfin identifié les zones où ces mesures seraient les plus efficaces, de même que les associations d'intervenants locaux susceptibles de les mettre en oeuvre. L'influence de la mise en oeuvre a été évaluée en utilisant le modèle selon trois scénarios. Cette étude illustre la pertinence des modèles d'érosion distribués pour concevoir des mesures de lutte contre l'érosion lorsque suffisamment d'informations sur les zones érodées, provenant d'enquêtes sur le terrain, sont disponibles. Les levés bathymétriques ont été fondamentaux pour valider la réponse du modèle à long terme, tandis que les mesures ponctuelles ont été utiles pour vérifier la variabilité spatiale des prévisions du modèle.
This work presents a probabilistic flow duration methodology that can be used as an alternative approach to the design and performance evaluation of small hydro plants. The probabilistic approach aims to quantify the uncertainty influencing the design and the economic outlook of small hydropower projects thus overcoming the limitations of the standard design methodology, which is based on a deterministic approach through the historical flow duration curve at the intake site. A simple probabilistic flow duration curve model is presented and an applied case study of the probabilistic approach to plant design and evaluation is provided based on a typical small hydro plant in a mountainous region of Greece. The results of this study however are not restricted to any particular geographical region and the methodology can be applied in a variety of hydrologic and economic environments. Keywords Flow duration curve . Small hydro plants . Probabilistic flow model . Log-normal distribution . Energy output . Financial risk . Environmental flow Notations Q Mean daily flow (m 3 /s) Q 0 Location parameter representing a lower boundary of flow (m 3 /s) a, b Parameters of LN distribution (annual) a f , b f Parameters of Normal distribution (global) Z u u-percentile of the standard normal variate s[ln(Q)] Standard deviation of log-transformed flows Water Resour Manage (
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