Co-management of floods and droughts for the adaptation of agricultural water supply to climate change

Climate change sees a shift from groundwater recharge to surface runoff caused by frequently occuring heavy precipitation events which exceed the infiltration capacity of the soil. Therefore, the impact of groundwater aquifers as buffer systems is reduced. At the same time the water demand for irrigation and cooling in agriculture is increasing. To compensate, water has to be transferred and ideally stored close to the demand to reduce costs for infrastructure. Even if water supply from major rivers which do not suffer from low water levels in dry periods is available peak demand and runoff are out of phase and peak volumes would require large water distribution systems. This is generally addressed by setting up large surface level basins with all their drawbacks (large spatial footprint, losses through evaporation, microbial contamination, stagnating waters).

One alternative adaptation strategy is to divert peak flow in surface waters and infiltrate directly into groundwaters to use them for storage during dry periods, as naturally occurring when high percolation rates are achieved. For this variant of managed aquifer recharge large aquifers with high hydraulic conductivity are required. Suitable sites have been identified using the multi-criteria decision analysis developed by [1]. Starting from the infiltration of flood peaks only, where the naturally occurring cycle of surplus water is reestablished, the concept can be extended to an active management of surface runoff while ensuring environmental sustainable flow regimes in the streams and small rivers.

Groundwater quality can be maintained using both pretreatment technologies and careful risk assessment of the catchment of the surface water. Analyses during the recent Vb weather condition in Bavaria indicate that the water quality is much better than expected and generally suitable for infiltration in phreatic aquifers.

The study site is located in Bavaria and well known for excellent soils for agriculture. Potatoes, sugar beets, and corn are the main crops grown with the potato being least resilient to increasing temperatures. Our site analysis showed a number of potential infiltration sites, and we identified several sources with enough excess water to sustain more than one dry year. The water is diverted from the river by pipelines and ditches and led to an infiltration basin surrounded by farmland. The small basin serves as a buffer for peak flow that would otherwise cause flooding. According to our hydrogeological models the infiltrated water will remain in the region and a long-term recharge of the aquifer seems possible. The favored setup will also reduce damages in downstream plots with higher groundwater levels caused by extended flooding.

The co-management of floods and low groundwater levels is applicable to streams and smaller rivers. Here, the risks in the catchment can be assessed and controlled. For water storage, natural storage in the underground is used. Based on our chemical analysis groundwater quality will benefit from the infiltration. Furthermore, the socio-economic aspects from farmers and other users are addressed and resilience for climate change is enhanced. 

[1] L. Augustin and T. Baumann: Suitability mapping for subsurface floodwater storage schemes, InterPore Journal 1(2), doi://10.69631/ipj.v1i2nr20.