Targeting of intervention areas to reduce reservoir sedimentation in the Tana catchment (Kenya) using SWAT

Abstract

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.

Sediment yield of the lower Tana River, Kenya, is insensitive to dam construction: sediment mobilization processes in a semi‐arid tropical river system

“…A similar line of reasoning is often maintained when interpreting sedimentary archives in alluvial plains and deltas, where the temporal evolution of sediments in the valley is often directly linked to land‐use changes on the catchment slopes and/or changes in climate (Hoffmann et al ., ; Macklin and Lewin, ). Finally, catchment management plans often aim to reduce sedimentation in reservoirs by implementing soil conservation measures in well‐targeted areas, again supposing that a direct link exists between sediment production and catchment yield (Hunink et al ., ).…”

Hydrological Modelling using Satellite-Based Crop Coefficients: A Comparison of Methods at the Basin Scale

“…However, as was shown previously, there can be considerable deviations with an approach using high-resolution information on crop status, as is provided by remote sensing, especially at the sub-basin scale. When outputs at smaller scale become the focal point of study, for example for prioritizing measures across the landscape [63], literature-based values will result in a loss of information and consequent inaccurate results. Figure 8 shows a comparison of all methods at the sub-basin scale.…”

Reaching out from the soil-box in pursuit of soil security

“…Obviously, convincing these companies to pay farmers is very difficult because the idea is quite new to them and they require quantitative studies supporting claims being made. Based on an available soil map, that was transformed in a map of Hydraulic Response Units, the hydrology of the basin was simulated with the SWAT (Soil and Water Assessment Tool) model, focusing on 11 well established soil conservation scenario's (WOCAT 2007) (Hunink et al 2012(Hunink et al , 2013Kauffman et al 2014). Figure 3 shows the georeferenced simulated results of the effects of the ridging scenario in terms of the expected decline of erosion rates (and a corresponding increase of Green Water) as compared with a baseline scenario describing actual conditions.…”