Mitigating floods and attenuating surface runoff with temporary storage areas in headwaters

Abstract

Temporary storage areas (TSAs) represent a category of soft-engineered naturebased solutions that can provide dispersed, small-scale storage throughout a catchment. TSAs store and attenuate surface runoff, providing new additional storage during flood events. The need for such additional catchment storage will become more urgent as the frequency and magnitude of extreme hydrological events increases due to climate change. Implementation of TSAs in headwater catchments is slowly gaining momentum, but practitioners still require further evidence on how such measures function during flood events. This review focuses on the role of relatively small-scale (<10,000 m 3 ) TSAs in headwater catchments for flood risk management. It also explores the potential wider benefits for implementing these as part of an integrated catchment management approach. TSA flood mitigation effectiveness is primarily determined by the TSA's available storage prior to the event. At the local scale, this can be represented by the relationship between TSA inputs, outputs and total storage. Factors influencing the local functioning and effectiveness of TSAs are discussed, with potential considerations for optimizing future TSA design and management. Hydrological models have suggested that TSAs could be used to effectively attenuate high magnitude events. However, future considerations should involve addressing the lack of empirical evidence showing TSA catchment scale effectiveness and how local TSA functioning might change in time. Small-scale headwater TSAs offer a holistic and sustainable approach to catchment management that can deliver both local benefits to landowners and wider flood risk mitigation for society.

Slowing Down Quick Runoff—A New Approach for the Delineation and Assessment of Critical Points, Contributing Areas, and Proposals of Measures to Reduce Non-Point Water Pollution from Agricultural Land

“…The correct identification of vulnerable sites was confirmed, in terms of surface runoff by a mathematical model, and in terms of subsurface runoff and water pollution by water quality monitoring, not only for this site of interest, but also elsewhere [60,75]. The list of proposed measures implemented in this paper is longer than that presented in similar studies [40][41][42][43][44][45]; nevertheless, the principles used to determine their precise location remain analogous. However, for studies conducted in the future, it is a priority to automate these principles as an easily applicable GIS tool.…”

“…The correct spatial targeting of the appropriate measures is necessary in terms of achieving successful implementation of programs to improve the ecological status of the agricultural landscape [78]. Recently, many studies focused on approaches for the delineation of risky areas and demonstration of methods for prioritization nature-close interventions on agricultural land to mitigate quick runoff and non-point water pollution sources at various scales [40][41][42][43][44][45]. The advantage of these methods is the applicability of a uniform methodology for identifying vulnerable areas with different spatial scales.…”

“…different landscapes within a watershed area [40][41][42][43][44][45]. At the same time, structural water retention measures provide an enhanced water storage capacity; therefore, they may generally be more effective for water quality improvements than agrotechnical measures [40][41][42].…”

“…In numerous cases, and especially in practice, runoff reduction interventions and water quality improvement measures are separately propounded or adopted solely for the selected individual measures [35][36][37][38][39]. Nevertheless, several complex approaches have been documented in the literature [40][41][42][43][44]. A comprehensive method utilized for identifying priority areas on a large scale, including agricultural drainage, was presented in a study conducted by [41], which assessed runoff and nitrate leaching processes using the SWAT model and GIS tools in risky areas, and accordingly positioned and evaluated seven types of structural measures in the study.…”

“…Several studies agreed that mitigation measures are the most effective method when designed and implemented as a mutually interconnected system of different measures in different landscapes within a watershed area [40][41][42][43][44][45]. At the same time, structural water retention measures provide an enhanced water storage capacity; therefore, they may generally be more effective for water quality improvements than agrotechnical measures [40][41][42].…”