Evaluating the effectiveness of catchment-scale approaches in mitigating urban surface water flooding

Abstract

<jats:p>The argument for natural flood management in the UK has strengthened in recent years with increasing awareness of the potential benefits gained from upstream interventions (especially improvements in water quality, public amenities and biodiversity). This study aims to develop an understanding of another potential benefit—interventions promoting free discharge at downstream urban drainage outfalls by moderating water levels in receiving watercourses. A novel, coupled model (linking dynamic TOPMODEL, HEC-RAS and Infoworks ICM) is calibrated for the Asker catchment in Dorset, England. This predominantly rural watershed drains to the town of Bridport, frequently submerging a surface drainage outfall in a nearby housing estate. Two forms of upstream, catchment-scale intervention (hillslope tree planting and in-channel large woody debris) are modelled to understand their impacts on the functioning of the drainage network during both the calibration period and a range of design storms. The results indicate that interventions have the greatest positive impact during frequent events. For example, during a storm with a 10% annual exceedance probability (AEP), upstream NFM could reduce outfall inundation by up to 3.75 h and remove any surcharging of flow within the drainage system in Bridport. In more severe storms, the results suggest interventions could slightly prolong the time the outfall was submerged. However, by slowing the wider catchment's response during the 3.3% AEP storm, upstream interventions allow more water to escape the urban drainage system and reduce the maximum surface flooding extent within the housing estate by 35%.</jats:p> <jats:p>This article is part of the theme issue ‘Urban flood resilience’.</jats:p>

A systematic review of natural flood management modelling: Approaches, limitations, and potential solutions

“…Adding to this, a lack of calibration data ( n = 21) was also noted as being a significant limitation. Lack of calibration data often stems from an absence of site‐specific data, such as the outflow of a certain NFM feature (Lin et al, 2021), or lack of data at the catchment scale, such as the absence of rain and flow gauging stations in smaller or more rural catchments (Ferguson & Fenner, 2020c). In most cases, while there was some form of data for calibration, this tended to be limited and only for a small number of low‐intensity events (Gülbaz & Kazezyilmaz‐Alhan, 2014; Schubert et al, 2017).…”

“…Further model integration has also been achieved by cascading different modelling approaches, which involves coupling semi-distributed or distributed hydrological models for catchment-wide hydrology with 1D or 2D hydraulic models for channel flow dynamics (Hankin et al, 2019;Rodríguez-Rinc on et al, 2015). This allows for a more realistic representation of water flows around in-channel features, such as leaky dams or barriers (Ferguson & Fenner, 2020c).…”

The potential for natural flood management to maintain free discharge at urban drainage outfalls

“…The fluxes through each were then extracted to give reach-by-reach inputs to the channel zone in the 2D HEC-RAS model. This replicates techniques followed in Hankin et al (2019) and Ferguson and Fenner (2020). The freely available 2D HEC-RAS module (which solves the full shallow flow equations using a finite element method) routed these flows across the 1 m resolution DTM to the downstream river gauge (using the diffusive wave approximation).…”

“…The rural response (i.e., upstream of the river level gauge) was characterised by coupling Dynamic TOPMODEL and HEC‐RAS (similar to methodologies described in [Hankin et al, 2019; Ferguson & Fenner, 2020]). Dynamic TOPMODEL evolved from TOPMODEL, a long‐established semi‐distributed, and semi‐conceptual hydrological model (Beven & Kirkby, 1979; Gayathri, Ganasri, & Dwarakish, 2015; Lane, Brookes, Kirkby, & Holden, 2004; Metcalfe, Beven, Hankin, & Lamb, 2018).…”

Editorial: great floods have flown from simple sources

“…The next two papers deal with different modelling approaches to examining aspects of urban flood resilience. Ferguson & Fenner [12] use a novel coupled model linking DynamicTOPMPODEL, HEC-RAS and Infoworks ICM to explore the effect of Natural Flood Management (NFM) interventions in the Asker catchment (Dorset, UK). Their paper investigates if moderating water levels in urban receiving watercourses can be achieved by NFM to allow free drainage at frequently submerged drainage outlets, in this case from a housing estate in Bridport.…”