SPES - Surveys and Predictions of Erosion and Siltation

Building a reservoir in a river brings environmental consequences both upstream, in the reservoir itself, and downstream. Many of these consequences are related to the trapping of sediments in the artificial lake. The useful storage of the reservoir decreases, while serious problems may arise downstream due to erosion.

A range of complicated processes interact, why a prediction of what will happen, as a result of the construction of a dam, is very difficult ­ albeit necessary. The predictions should be followed up after construction, and a long-term monitoring program be established as soon as possible. We offer these services, either separately, or as a complete package.

Sediment dynamics may also be of concern along coasts, deltas, and beaches. Refer to our coastal zone page for more information about related offers.

We Offer...

Pre-feasibility and feasibility studies of planned reservoirs
Prediction of the trapping efficiency of planned reservoirs
Verification of trapping efficiency after reservoir construction
Establishment of a monitoring program including training
Studies of problems with sediments reaching the turbines
Studies of downstream bank, delta, and shoreline erosion
Drainage area investigations of sediment production
Problems of floating peat islands in reservoirs
Research on special issues related to the physical environment

the Arenal volcano and reservoir
The Arenal Volcano and Reservoir, Costa Rica

State-of-the-Art Tools and Methods

Precision echo-sounding Sediment inflow and outflow
X-ray sediment analysis Side scan sonar mapping
Sedimeter® measurements Turbidity measurements
Trapping efficiency modelling Flood frequency modelling

Sediment X-raying

The stratigraphy of soft, recent, sediments may be studied by coring and 'quantitative X-raying', a method developed by Valter Axelsson. The result may be used for quantifying reservoir sedimentation (even at a very early stage of reservoir operation), for stratigraphic correlations, and for a significantly improved sampling for the analysis of pollutants.

Prediction of trapping efficiency

We have ample experience from measuring the sediment-related processes in reservoirs: river discharge, sediment concentration, turbidity currents, sedimentation rates, sediment compaction. Using dedicated software we can make predictions for trapping efficiency of planned reservoirs, and using the Sedimeter® the results may be checked at a very early stage of operation, thanks to the high resolution.

Example: Arenal Reservoir, Costa Rica

GIS showing erosion risk areasSediment sources in the drainage area are identified, and a risk map produced for land use planning
Discharge and turbidity data needs to be evaluated carefully to determine the representativity of the dataFlood loops from a measurement station
Levelling over a deltaTopographic surveying of the delta development - here with traditional and proven methods
Using side scan sonar a map of the bottom can be made, showing relief, sediments, etcSonar recording showing sediment variations
X-ray of a sediment coreX-rays of sediment cores reveal the sedimentation history, and the bulk density of the sediments

We Offer Solutions - Not Just Data