Abstract
It is well known that soil, hillslopes, and watercourses in small catchments possess a degree of natural attenuation that affects both the shape of the outlet hydrograph and the transport of nutrients and sediments. The widespread adoption of Natural Based Solutions (NBS) practices in the headwaters of these catchments is expected to add additional attenuation primarily through increasing the amount of new storage available to accommodate flood flows. The actual type of NBS features used to add storage could include swales, ditches, and small ponds (acting as sediment traps). Here, recent data collected from monitored features (from the Demonstration Test Catchments project in the Newby Beck catchment (Eden) in northwest England) were used to provide first estimates of the percentages of the suspended sediment (SS) and total phosphorus (TP) loads that could be trapped by additional features. The Catchment Runoff Attenuation Flux Tool (CRAFT) was then used to model this catchment (Newby Beck) to investigate whether adding additional attenuation, along with the ability to trap and retain SS (and attached P), will have any effect on the flood peak and associated peak concentrations of SS and TP. The modelling tested the hypothesis that increasing the amount of new storage (thus adding attenuation capacity) in the catchment will have a beneficial effect. The model results implied that a small decrease of the order of 5–10% in the peak concentrations of SS and TP was observable after adding 2000 m3 to 8000 m3 of additional storage to the catchment.
Highlights
IntroductionIt is becoming widely accepted that Nature Based Solutions (NBS—Nature Based GreenInstructure Solutions) [1] and “Natural Flood Management” (NFM) (defined by the United KingdomEnvironment Agency as part of Working with Natural Processes) [2] can have a positive impact in terms of reducing flooding, most observably by lowering the peak discharge of the flood hydrograph to enable this [3,4,5,6,7]
It is becoming widely accepted that Nature Based Solutions (NBS—Nature Based GreenInstructure Solutions) [1] and “Natural Flood Management” (NFM) [2] can have a positive impact in terms of reducing flooding, most observably by lowering the peak discharge of the flood hydrograph to enable this [3,4,5,6,7]
The Catchment Runoff Attenuation Flux Tool (CRAFT) had already been calibrated to baseline conditions during October 2011–September
Summary
It is becoming widely accepted that Nature Based Solutions (NBS—Nature Based GreenInstructure Solutions) [1] and “Natural Flood Management” (NFM) (defined by the United KingdomEnvironment Agency as part of Working with Natural Processes) [2] can have a positive impact in terms of reducing flooding, most observably by lowering the peak discharge of the flood hydrograph to enable this [3,4,5,6,7]. Previous studies of the performance of features have concentrated primarily on the attenuation capabilities of these features in terms of reducing flooding, e.g., Belford Burn [9] and Pickering Beck [4,10] (in the U.K.). The improvement in water quality (quantifiable by a reduction in concentrations and/or loads of nutrients and sediments) brought about by the construction of features in rural catchments has been studied in the U.K. Avery [16] coined the term “rural sustainable drainage systems” (RSuDS) to reflect the trend to construct wetlands and other types of features in rural catchments, and since the focus of this study is on the use of mitigation features to improve water quality rather than NFM per se, the term. The design purpose of RSuDs by default leads to sediment trapping and P stripping and associated “buffering” of other chemicals and microbial pollutants
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