HYPOS Newsletter – Issue 2, November 2022

Figure 1: Visualize your data with map views and time series plots

Get a first glance at the data – from your own in-situ data to hydrological parameters from models to spatial grid data from the satellites (Figure 1). Aggregate the satellite data for polygons defined by you to get deeper insights. Plot time series of all data together to better understand your catchment. Transect plots for different dates reveal the changes within a reservoir or along a river.

The HYPOS portal can notify you if certain thresholds are exceeded. Once you define thresholds for each parameter (e.g. turbidity), the system displays the exceedances in a dashboard with all your virtual stations (polygons defined by the user). This allows you to see which parts of the catchment are currently above the limits and how often they have been in the past. By selecting one station/polygon, you will be able to analyse the data even deeper with time series plots and two synchronized maps. The system will also automatically notify you via e-mail when thresholds are exceeded in near-real-time (NRT, usually within less than 24 h).

The data provided in the portal allows you to calculate sediment fluxes at any point in the river. Sediment fluxes are the product of discharge and sediment concentrations (SSC). The discharge can either come from in-situ measurements, if available, or from the global or locally customized hydrological models developed using Hydrological Predictions for the Environment (HYPE) in daily resolution. The sediment concentrations can be provided by the satellite measurements of turbidity (TUR) with a transfer function. This transfer from TUR to SSC can be done with a global formula or with a localised function if field measurements of SSC are available for calibration.

Figure 2: Schematic setup of sediment flux calculation within the HYPOS tool.

Since the SSC from satellites is usually not available every single day, the SSC can also be estimated from the continuous discharge measurements with a power regression. HYPE model provides daily estimates of SSC as well as sediment fluxes at selected points. With this approach it is possible to retrieve sediment fluxes for long time periods. A typical setting with some (short term) SSC data measured with an in-situ station is sketched in Figure 2. The first step is to calibrate the satellite derived turbidity values with in-situ SSC values to retrieve a correlation that can later be applied anywhere in the river (upstream section on the right). The combination of SSC from satellites and discharge from the model can be used to retrieve sediment fluxes at the inflow and the outflow of the reservoir (orange arrows). This finally allows to estimate the sediments that are held back in the reservoir.

The Blue Water Footprint (BWF) is an indicator that builds on the ratio between evaporated water from the reservoir and the power production in the HPP. It is thus a measure of the water “lost” by the reservoir. The BWF is influenced by the climatic conditions and the reservoir surface area of the respective site (evaporation) and the power generated in the power plant. The evaporation can be calculated from satellites to build a monthly mean evaporation value. This is then divided by the monthly power production to retrieve a monthly BWF. The water lost due to evaporation impacts the productivity of the power plant, as well as downstream water availability for other purposes (irrigation, drinking water, ecological impacts).

The sediment flux approach described above was applied in the Devoll river and compared to a sediment flux calculated from both in-situ discharge and SSC. The results showed an overestimation of 23 % by the HYPOS approach over a 3-year period. While the HYPOS approach delivers data for every day of the year, the in-situ station only provided data for 62 % of the days. The costs for the HYPOS solution were around 10 % of the costs for the in-situ stations’ setup and maintenance.

These are the key results from the Banja use case:

The Rhône flows out of Lake Geneva and runs through a cascade of hydropower plants in both Switzerland and France. Flushing operations are challenging and need proper planning to ensure a propagation of the sediment flow through all dams. Additionally, strict thresholds for SSC need to be maintained to avoid environmental impacts like fish kills. The satellites enable a total surveillance of the river during flushing operations, including all side arms and ponds (see Figure 3). Along the Rhône, the propagation of sediment-laden waters can be observed in near-real-time.

The key result from the Rhône use case: