Catchment-scale assessment of small retention ponds as nature-based solutions in a Norwegian agricultural catchment using SWAT+

Small retention ponds are increasingly recognised as effective nature-based solutions for managing hydrological extremes in Norway’s agricultural catchments. Typically located in upper catchment areas or at the forest–agriculture interface, these ponds temporarily store runoff during intense rainfall events and snowmelt. In addition to flood mitigation, they provide important co-benefits by reducing soil erosion and sediment transport and by protecting agricultural drainage systems from erosion and overflow during extreme events, thereby supporting long-term soil productivity. Although individual storage volumes are limited, their cumulative impact at the catchment scale can be substantial when retention ponds are strategically distributed across the landscape. 

This study investigates the potential effects of small retention ponds using process-based hydrological modelling with SWAT+ to support catchment-scale climate adaptation planning in a Norwegian agricultural catchment. SWAT+ enables an improved representation of hydrological connectivity between managed landscapes and the stream network through its flexible spatial structure and rule-based management algorithms. The model is calibrated using a constraint-based approach that integrates both soft and hard data to represent streamflow and sediment dynamics in the Lierelva catchment. Multiple retention ponds are implemented to assess their cumulative effects on streamflow and sediment transport. Finally, the study discusses key challenges associated with modelling catchment–NBS interactions using SWAT+.