Innovate UK: Improved probabilistic mapping and modelling of groundwater flooding in urban areas
Lead Research Organisation:
British Geological Survey
Department Name: Environmental Modelling
Abstract
There is a need to better understand the role of groundwater in urban flooding - a quarter of claims following the most recent major flooding (winter 2013/14) were associated with flooding predominantly from a 'groundwater' mechanism. Additionally, existing groundwater mapping solutions, do not quantify the expected degree of impact of flooding expected for a given return period - rather a high/med/low classification. We will create a novel software tool that allows for the dynamic simulation of surface and groundwater flow, over a wide area. Currently such a tool which represents the entire water-system does not exist in a dynamic form (i.e. where the two layers react and change with one-another over time).
There are two main types of groundwater flooding: Permeable Superficial Deposits (PSD) driven by surface water flooding and Clearwater flooding where the groundwater table cuts the groundwater surface. The former, PSD, occurs when superficial deposits transmit the flood wave and results in groundwater flooding outside that identified by traditional flood risk approaches. The latter can take the form of surface ponding as well as flowing features. These two distinct types of groundwater flooding require two different approaches:
1. PSD - surface water levels in rivers, streams and drains will drive the groundwater head. Therefore a method needs to be developed that links the surface water heads to groundwater heads.
2. Clearwater - Based on the method developed by Upton and Jackson (2011; http://nora.nerc.ac.uk/13501/) to produce a dynamic groundwater surface produced from groundwater point models (AquiMod).
Once the appropriate groundwater heads are produced these can be combined with a DTM to produce a revised groundwater flood map. lumped parameter groundwater models for Permeable Superficial Deposits (PSD) and Clearwater flooding on the Chalk will be developed. The two suggested areas are Oxford for PSDs and Kenley/Croydon for Clearwater flooding. The former (PSD) will need to develop a linkage with Ambiental surface water models to drive the groundwater response and the latter can feed into flood extent models.
Once the integrated system has been developed then the following will be undertaken:
1. Assessment of areas prone to flooding - this will take the form of using OpenData (BGS geological maps, Environment Agency groundwater level data, OS data) to develop risk maps for groundwater flooding.
2. Regional assessment of PSD and Clearwater flooding - by extending the modelling approach applying this to the flood prone areas identified in (1).
3. Climate change impacts and changes to flood risk probability.
There are two main types of groundwater flooding: Permeable Superficial Deposits (PSD) driven by surface water flooding and Clearwater flooding where the groundwater table cuts the groundwater surface. The former, PSD, occurs when superficial deposits transmit the flood wave and results in groundwater flooding outside that identified by traditional flood risk approaches. The latter can take the form of surface ponding as well as flowing features. These two distinct types of groundwater flooding require two different approaches:
1. PSD - surface water levels in rivers, streams and drains will drive the groundwater head. Therefore a method needs to be developed that links the surface water heads to groundwater heads.
2. Clearwater - Based on the method developed by Upton and Jackson (2011; http://nora.nerc.ac.uk/13501/) to produce a dynamic groundwater surface produced from groundwater point models (AquiMod).
Once the appropriate groundwater heads are produced these can be combined with a DTM to produce a revised groundwater flood map. lumped parameter groundwater models for Permeable Superficial Deposits (PSD) and Clearwater flooding on the Chalk will be developed. The two suggested areas are Oxford for PSDs and Kenley/Croydon for Clearwater flooding. The former (PSD) will need to develop a linkage with Ambiental surface water models to drive the groundwater response and the latter can feed into flood extent models.
Once the integrated system has been developed then the following will be undertaken:
1. Assessment of areas prone to flooding - this will take the form of using OpenData (BGS geological maps, Environment Agency groundwater level data, OS data) to develop risk maps for groundwater flooding.
2. Regional assessment of PSD and Clearwater flooding - by extending the modelling approach applying this to the flood prone areas identified in (1).
3. Climate change impacts and changes to flood risk probability.
Planned Impact
The BGS has one of the largest groups of scientists internationally researching groundwater flooding. This includes aspects such as the understanding of groundwater flooding mechanisms, modelling of groundwater flooding and the mapping of susceptible areas. However the tools and techniques for groundwater flood risk mapping are still being developed. This project offers a unique opportunity for BGS staff to work with colleagues in the flood risk industry to address this gap. This will have benefit to BGS science both in terms of improving the understanding and simulation of surface water and groundwater interaction under extreme conditions and the impact of its work.
Given the importance of this process, a range of different methods will be used to disseminate the results from the study: websites, conference presentations and peer reviewed publications. Dissemination of this work will be undertaken through the BGS website via the Environmental Modelling Directorate and dedicated groundwater flooding webpages. The project report and any journals will be made available using NERC's online research repository (nora.nerc.ac.uk). BGS' staff attendance at conferences will be exploited through presentations at EGU (March 2016) and iEMSs (http://www.iemss.org /sites/iemss2016/; July 2016). Ultimately impact will be measured by the inclusion of BGS and NERC science into a flood risk product creating kudos through its use and generating commercial income.
Given the importance of this process, a range of different methods will be used to disseminate the results from the study: websites, conference presentations and peer reviewed publications. Dissemination of this work will be undertaken through the BGS website via the Environmental Modelling Directorate and dedicated groundwater flooding webpages. The project report and any journals will be made available using NERC's online research repository (nora.nerc.ac.uk). BGS' staff attendance at conferences will be exploited through presentations at EGU (March 2016) and iEMSs (http://www.iemss.org /sites/iemss2016/; July 2016). Ultimately impact will be measured by the inclusion of BGS and NERC science into a flood risk product creating kudos through its use and generating commercial income.
| Description | Used to inform data product development in BGS |
| First Year Of Impact | 2017 |
| Sector | Government, Democracy and Justice |
| Impact Types | Economic |
| Description | Technology Strategy Board: Infrastructure Systems over 12 months or over £100k (12-24 Months) |
| Amount | £109,637 (GBP) |
| Funding ID | 82768-509397 |
| Organisation | Innovate UK |
| Sector | Public |
| Country | United Kingdom |
| Start | 04/2017 |
| End | 06/2018 |
| Title | Permeable Superficial Deposit - Groundwater simulation |
| Description | The premise of Permeable Superficial Deposits (PSD) or groundwater exacerbated flooding is that elevated river and stream levels (stage) create a head difference with the surrounding aquifer. During the time that the river stage in the main channel is elevated behind flood defences and/or minor streams flow due to excess flood waters then a "pulse" of head will be transmitted through the permeable deposits. This results in elevated heads throughout the groundwater system which, where the groundwater head is above the ground surface results in groundwater flooding. Once river stage increases during a high flow or flood event then water is "pushed" through the superficial deposits and groundwater head increases and results in groundwater flooding in topographic lows. To be able to simulate the distribution of groundwater heads there are a number of options. Distributed, deterministic models produce a groundwater surface which varies in time and space, but are data hungry and take resources to develop. Analytical solutions whilst they have limiting assumptions, such as homogeneity of the porous media, are computationally efficient and can be applied where data are scarce. For preliminary modelling of groundwater flow in PSDs it is proposed that an analytical solution is the best approach. The PSD methodology will be based on the analytical solution by Moench and Barlow (2000) which solves the 2D (x-z) groundwater flow equation for an instantaneous rise in river stage. Using Laplace transforms the rise in head in an x-z section of an unconfined aquifer can be calculated. Use of an x-z section allows groundwater head to be calculated for a given depth or over the full thickness of the PSDs. MOENCH, A. F., & BARLOW, P. M., 2000. AQUIFER RESPONSE TO STREAM-STAGE AND RECHARGE VARIATIONS. I. ANALYTICAL STEP-RESPONSE FUNCTIONS. JOURNAL OF HYDROLOGY, 230(3), 192-210. |
| Type Of Material | Computer model/algorithm |
| Provided To Others? | No |
| Impact | This code, when coupled to the project partners, surface water code has the potential to change how flood modelling is undertaken. |
| Title | Simple Clearwater flood methodology |
| Description | There are two types of groundwater flooding: Clearwater and that from Permeable Superficial Deposits (PSD). The former is where increased rainfall results in greater input (recharge) to the groundwater system and the water table rises and cuts the land surface. The latter is driven by a rise in river stage which is propagated through the more permeable deposits underlying the flood plain. The two types are dependent on different geological / hydrogeological setting. PSD flooding are more likely to be associated with urbanised areas, given cities are developed close to major rivers. However, both types of groundwater flooding Increases the likelihood of flooding and poses a threat to homes, business and infrastructure. A methodology has been created that has been used to generate a series of groundwater level surfaces in ascii file format which represent conditions that occurred during winter 2013/2014 flood in Croydon/Kenley. |
| Type Of Material | Computer model/algorithm |
| Provided To Others? | No |
| Impact | This modelling approach, when coupled with the partners surface water model, has the potential to change how flood risk is calculated. |
| Description | stakeholder meetings |
| Form Of Engagement Activity | A formal working group, expert panel or dialogue |
| Part Of Official Scheme? | No |
| Geographic Reach | Regional |
| Primary Audience | Industry/Business |
| Results and Impact | meeting with 2 main stakeholders intereseted in developing, influencing and using the research into flood risk analsysis. the meeting's aim was to capture the stakeholder's specific and generic industry needs to ensure that the reseach and development is strongly aligned with business needs. the meeting sucessfully estbalished these needs and helped to prioritise case study focus. |
| Year(s) Of Engagement Activity | 2015,2016 |