Decreasing Demand Affects Bank Filtrate

In Germany in 2007, the main sources of water were groundwater and spring water (70%), surface water and artificial infiltrate (22%) and bank filtrate (8%). Bank filtrate as a raw water source is used for both drinking water supply and process water. The water quality of pumped raw water from bank filtration sites depends on the water quality of the infiltrating surface water and the landside groundwater, the proportions of each and the flow and transport conditions in the aquifer.

Due to the intensive agricultural use of the landside catchment, high portions of landside groundwater may result in increased concentrations of nitrate, sulphate, hardness and pesticides. Poor quality of river water, in combination with high loads of suspended matter, may also result in river bed clogging. While the clogging layer comprises the biologically most active layer, it also strongly reduces water infiltration if the hydraulic conductivity decreases.

According to an article in Drinking Water and Engineering and Science by Grischenk et al., reduced water abstraction (due to the decline in water consumption and thus water production) results in a lower portion of bank filtrate in the abstracted raw water. The quality of the landside groundwater therefore becomes more important for the subsequent water treatment.

Optimisation of well operation to cover the lower mean demand and the remaining peak demand therefore becomes a key issue in the management of bank filtration sites. Under other hydrogeological or other socio-political conditions, flow conditions such as mixing behaviour, groundwater flow beneath the river and travel times should be investigated by groundwater flow modelling prior to any planning, construction or optimisation of bank filtration sites.