Evaluation of reservoir sedimentation as a methodology for ...

6. Conclusions: Monitoring soil loss and sediment transport at the basin
scale
Altogether, it can be concluded that reservoir sedimentation data are a valuable tool
for monitoring sediment dynamics at the basin scale and assess problems related the
loss of storage capacity and of sediment export to rivers downstream as well as to
coastal areas. Furthermore, reservoir sedimentation data also can provide insight in
sediment dynamics within the basin, though no information is obtained on the spatial
distribution of sediment sources. For insight in the spatial pattern of erosion and
sedimentation probably tracer studies in combination with modelling are the most
appropriate. Nevertheless, for modelling at the basin scale very few models exist
that are capable to incorporate both erosion and sediment delivery accurately, and
these models will require data on sediment yield at various scales for calibration and
validation.
The methodology of bathymetric surveys is well developed and is generally seen as
the best available method to assess basin sediment export, though with the
limitation that it can of course only be applied when a reservoir is present. Further,
in assessment of reservoir sedimentation it is important that the reservoir is in
operation long enough to include also the rare event and the trap efficiency should
be included in calculations. In order to assess the bulk density sufficient sediment
samples should be taken.
Basin sediment yield reflects all erosion and deposition processes within a basin and
thus reservoir sedimentation rates can not be compared directly with for example
soil loss measurements from runoff plots as different erosion and deposition
processes are measured. Important for interpretation is further that reservoir
sedimentation rates represent the long-term average sediment export of a basin and
therefore do not necessarily reflect all environmental changes occurring within a
drainage basin.
References
Avendaño Salas, C. and Calvo Sorando, J.P., 1994. La modelización matemática, ajuste y contraste del
coeficiente de entrega de sedimentos a los embalses. Aplicación al cálculo de la erosión de
cuencas fluviales., La Fundación Universidad Empresa and CEDEX, Madrid.
Avendaño Salas, C. and Cobo Rayán, R., 1997. Metodología para estimar la erosion de cuencas fluviales a
partir de la batimetría de embalses. In: J.J. Ibánez, B.L. Valero Garcés and C. Machado (Editors),
El paisaje mediterráneo a través del espacio y del tiempo. Implicaciones en la desertificación.
Geoforma Ediciones, Logroño, pp. 239-257.
Avendaño Salas, C., Cobo Rayán, R., Gómez Montaña, J.L. and Sanz Montero, E., 1995. Procedimiento
para evaluar la degradación específica (erosión) de cuencas de embalses a partir de los
sedimientos acumulados en los mismos. Aplicación al estudio de embalses Españoles. Ingeniería
Civil 99, 51-58.
Brown, C.B., 1943. Discussion of Sedimentation in reservoirs, by J. Witzig. Transactions of the American
Society of Civil Engineers 69, 1493-1500.
CEDEX, 1992. Informe sobre la situación de los estudios de aforo de solidos, batimetria y sedimentologia
de embalses hasta 1992. Centro de Estudios Hidrográficos del CEDEX, Madrid, pp. 38.
Church, M. and Slaymaker, H.O., 1989. Disequilibrium of Holocene sediment yield in glaciated British
Columbia. Nature 337, 452-454.
Dedkov, A.P. and Moszherin, V.T., 1992. Erosion and sediment yield in mountain areas of the world. In:
D.E. Walling, T.R. Davies and B. Hasholt (Editors), Erosion, debris flows and environment in
mountain regions. IAHS publication No. 209, Chengdu, pp. 29-36.
144