Rainfall Inputs and Downstream Modelling

Estimating rainfall is trickier than most people express, but accurate estimates are very important for several applications, one of the most obvious being hydrological models which calculate an estimate of river flows from a catchment, and when these flows will arrive. They are crucial for the management of resources and the prediction of flood and drought risks.

However, the type and form of rainfall estimate used can impact on the reliability of the output from the hydrological model. For example, satellite estimates used in regions where more accurate ground-based methods are not available, contain a lot of uncertainty at resolutions useful for modelling, and often an ensemble approach is used. This is when lots of scenarios are produced, each equally correct based on the information we know (and don’t know!) but different. When each is used as an input for the model you get a large number of outputs which can be used to calculate statistical data about the river flows, such as the likelihood of a flood occurring.

Whatever the source of the rainfall input, the way it is applied to the downstream model can also impact on the outputs. If a sudden, short term storm is simulated in the model as a daily total input this is likely to produce a different hydrograph (pattern of river flows over time) than if it was simulated as fifteen minute totals.

My principal area of research is investigating how these nuances of rainfall, be at the resolution it is applied or the errors associated with them, influence the applications to which they are applied.

Flash Flooding in the South Tyne, UK

As part of the SINATRA project I have been conducting research within the catchments of the South Tyne, UK. These small upland catchments have shown to be susceptible to flash flooding in the past, and my research is an attempt to model the geomorphic impact of these events on the catchments. The main focus so far has been on the Thinhope Burn catchment, supported by fieldwork, led by Dr David Milan of the University of Hull.

View of Thinhope Burn from the TLS base station

View of Thinhope Burn from the TLS base station

The fieldwork was also supported by members of the Flood Action Team (FloAT), from Newcastle University, part of the SINATRA project. A terrestrial laser scanner (TLS) was used to scan a 500m reach of the catchment to produce an elevation map that will be used to assist the modelling work using the CAESAR-Lisflood model.

Point cloud elevation of Thinhope Burn taken using TLS

Point cloud elevation of Thinhope Burn taken using TLS

Thinhope Burn was the site of a flash flood in the summer of 2007 which was highly geomorphically active, in that the very nature of the channel was altered, long standing features were destroyed and vegetation was washed away. In 2014, the channel still shows little signs of recovery and even evidence of further reworking. We hope to learn more about the long-term impacts of these events and how they impact of similar events in the future.

The Humber

I grew up and was raised on the south bank of the Humber, in Barton-upon-Humber (“Jewel of the South Bank”), so I was very privileged to be offered the chance to work on the Dynamic Humber Project (DHP) as a numerical modeller. As part of the role I was enhancing and testing the CAESAR-Lisflood model for use in the Humber Estuary to forecast its long-term development.

It was during this work that the estuary was struck by a storm surge on December 5th, 2013, which resulted in extensive flooding in the area. The modelling work was turned to reproducing the storm surge and the flooding it caused. This work has led to further work with the Environment Agency to model the impact of existing and proposed flood defences on the event and the flooding.

Prof Tom Coulthard and Dr Stuart McLelland laser scanning Spurn Point

Prof Tom Coulthard and Dr Stuart McLelland laser scanning Spurn Point

The original goal of forecasting the long-term future of the Humber Estuary has not been cast aside, though. The storm surge caused extensive damage to the spit of Spurn Point, punching a breach across the spit and its long-term future is uncertain. In the spirit of former University of Hull Geography Lecturer, George de Boer, myself and a small group of staff at Hull are monitoring Spurn Point and preparing for modelling work to predict its near and long-term future.

The breach along Spurn Point

The breach along Spurn Point

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