Abstract
Pluvial (surface water) flooding is often the cause of significant flood damage in urbanareas. However, pluvial flooding is often overlooked in catchments which are historically knownfor fluvial floods. In this study, we present a conceptual remote sensing based integrated approachto enhance current practice in the estimation of flood extent and damage and characterise the spatialdistribution of pluvial and fluvial flooding. Cockermouth, a town which is highly prone to flooding,was selected as a study site. The flood event caused by named storm Desmond in 2015 (5-6/12/2015)was selected for this study. A high resolution digital elevation model (DEM) was produced from acomposite digital surface model (DSM) and a digital terrain model (DTM) obtained from theEnvironment Agency. Using this DEM, a 2D flood model was developed in HEC-RAS (v5) 2D forthe study site. Simulations were carried out with and without pluvial flooding. Calibrated modelswere then used to compare the fluvial and combined (pluvial and fluvial) flood damage areas fordifferent land use types. The number of residential properties affected by both fluvial and combinedflooding was compared using a combination of modelled results and data collected from UnmannedAircraft Systems (UAS). As far as the authors are aware, this is the first time that remote sensingdata, hydrological modelling and flood damage data at a property level have been combined todifferentiate between the extent of flooding and damage caused by fluvial and pluvial flooding inthe same event. Results show that the contribution of pluvial flooding should not be ignored, evenin a catchment where fluvial flooding is the major cause of the flood damages. Although theadditional flood depths caused by the pluvial contribution were lower than the fluvial flood depths,the affected area is still significant. Pluvial flooding increased the overall number of affectedproperties by 25%. In addition, it increased the flood depths in a number of properties that wereidentified as being affected by fluvial flooding, in some cases by more than 50%. These findingsshow the importance of taking pluvial flooding into consideration in flood management practices.Further, most of the data used in this study was obtained via remote sensing methods, includingUAS. This demonstrates the merit of developing a remote sensing based framework to enhancecurrent practices in the estimation of both flood extent and damage.
Highlights
Flood events in England are estimated to cause damage losses to residential and non-residential properties of more than £1 billion pounds annually (2008 values) [1]
Fluvial flooding occurs as a result of water overtopping the river banks when the channel cannot cope with the water draining into it, whilst pluvial flooding occurs as a result of heavy rainfall overwhelming the drainage capacity of a local area [1]
The flood depths associated with the pluvial flooding, in this case, are less than those associated with the fluvial flooding, a large proportion of the affected area was impacted by pluvial flooding resulting in significant damage
Summary
Flood events in England are estimated to cause damage losses to residential and non-residential properties of more than £1 billion pounds annually (2008 values) [1]. Flooding that affects properties arises from different sources including coastal, fluvial and pluvial. Fluvial flooding occurs as a result of water overtopping the river banks when the channel cannot cope with the water draining into it, whilst pluvial flooding occurs as a result of heavy rainfall overwhelming the drainage capacity of a local area [1]. Across England, the Environment Agency (EA) estimates that there are 2.7 million properties at risk of fluvial and coastal flooding, three million properties at risk of pluvial flooding and 660,000 at risk from all sources (coastal, fluvial and pluvial) [1]. Considerable effort has been invested in damage data collection, data analysis and model development to investigate coastal and fluvial floods
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