Riparian buffer strips and their effectiveness as a natural flood management measure

Abstract

Riparian buffer strips are an established land management measure utilised to address diffuse pollution from agriculture and improve ecology. Previous studies have emphasised the multiple benefits of riparian buffer strips such as nutrient filtration and sediment trapping, which can be transported in overland flow and implies runoff is attenuated. Riparian buffer strips are not explicitly considered a natural flood management (NFM) measure. Nonetheless, they have the potential for inclusion to the catalogue of nature-based measures being implemented to reduce runoff and flood risk, while offering multiple benefits. An ecosystem services (ES) approach can be adopted to assess NFM multiple benefits (as multiple ES) and this study utilises a subset of ES to provide an example of this. Regulating and supporting ES were utilised to determine the effectiveness of riparian buffer strips as an NFM measure. At field scale, an experimental approach assessed flood regulation by monitoring runoff attenuation in a riparian buffer strip situated on an agricultural hillslope. An indication of nutrient cycling and primary production conditions at field scale was achieved by monitoring algae biomass and comparing a buffered and non-buffered site. The interaction between precipitation events, land management changes and nutrient concentrations were considered at the buffered site in relation to runoff attenuation and algae biomass response. At catchment scale, the Soil and Water Assessment Tool was utilised to explore reduction in peak flow (flood regulation) in response to varying scenarios of catchment-wide riparian buffer strips in terms of width and vegetation type. The empirical field observations demonstrated the riparian buffer strip provided runoff attenuation. Higher volumes of runoff coincided with bare soils in the adjacent field, wetter antecedent conditions, higher precipitation depths and intense precipitation. However, runoff attenuation could be improved. On the hillslope, microtopography of vehicle tracks diverted overland flow away from the buffer but the field corner demonstrated potential for a complimentary runoff attenuation feature (e.g. a temporary storage pond). At catchment scale, the 10 m grass-based buffer strip was concluded to be most effective for flood regulation and achieve a greater ratio of peak flow reduction (average 7.2%) to area of land required (2.1% of catchment). The riparian buffer strip demonstrated marginally better ecological quality conditions for nutrient cycling and primary production compared to the non-buffered site. Buffer shading positively affected the supporting ES. The study suggested high flows as a likely dominant influence on algae biomass. Overall, riparian buffer strips were concluded to be an effective NFM measure at field and catchment scale but could be improved with complimentary measures when located on a hillslope.