Exploring the Capability of Natural Flood Management Approaches in Groundwater-Dominated Chalk Streams

Imogen Barnsley,David Sear,Rebecca Spake,Justin Sheffield,Julian Leyland,Tim Sykes

doi:10.3390/w13162212

Abstract

This study aims to address the gap in the Natural Flood Management (NFM) evidence base concerning its implementation potential in groundwater-dominated catchments. We generated a typology of 198 chalk catchments using redundancy analysis and hierarchical clustering. Three catchment typologies were identified: (1) large catchments, (2) headwater catchments with permeable soils, and (3) catchments with impermeable soils and surfaces (urban and suburban land uses). The literature suggests that natural flood management application is most effective for catchments <20 km2, reducing the likelihood of significant flood mitigation in large catchments. The relatively lower proportion of surface runoff and higher recharge in permeable catchments diminishes natural flood management’s likely efficacy. Impermeable catchments are most suited to natural flood management due to a wide variety of flow pathways, making the full suite of natural flood management interventions applicable. Detailed groundwater flood maps and hydrological models are required to identify catchments where NFM can be used in a targeted manner to de-synchronise sub-catchment flood waves or to intercept runoff generated via groundwater emergence. Whilst our analysis suggests that most chalk groundwater-dominated catchments in this sample are unlikely to benefit from significant flood reductions due to natural flood management, the positive impact on ecosystem services and biodiversity makes it an attractive proposition.

Highlights

Natural Flood Management (NFM) represents a paradigm of management strategies that aim to improve a catchment’s resilience to prolonged and/or heavy rainfall by restoring, enhancing, or altering a catchment’s natural hydrological and morphological characteristics [1]
The cluster classifications are used as a screening process to identify which NFM interventions can theoretically be applied or ruled out of each catchment typology based on the dominant physical catchment properties identified by that group as shown on the redundancy analysis (RDA) plot (Figure 4)
The results of a redundancy analysis model were used to generate a typology of chalk catchments, resulting in three groupings according to broadly similar river regimes and physical catchment properties

Summary

Introduction

Natural Flood Management (NFM) represents a paradigm of management strategies that aim to improve a catchment’s resilience to prolonged and/or heavy rainfall by restoring, enhancing, or altering a catchment’s natural hydrological and morphological characteristics [1]. The demand for NFM implementation has increased due to its perception as a relatively low cost, low maintenance flood mitigation solution that protects and maintains hydrological and biological function of the rivers in which it is implemented [1,11,12]. Despite this growing demand for NFM interventions, the NFM evidence base consistently cites groundwater-dominated river systems, like chalk streams, as a gap in the knowledge due to hydrological differences, meaning the current evidence may not be directly applicable [11,13,14]

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