Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

LONG WHATTON & DISEWORTH FLOOD RISK MITIGATION &

RESILIENCE STUDY Final Model Report

AUGUST 2020

CONTACTS

SIMON AINLEY Project Manager

dd +01752 689006 Arcadis. e [email protected] 34 York Way London N1 9AB

VERSION CONTROL

Version Date Author Checker Approver Changes

01 09/06/2020 S Ainley J Sourbutts N McClung First Issue

02 16/07/2020 S Ainley J Sourbutts N McClung Second Issue

03 25/08/2020 S Ainley J Sourbutts N McClung Second Issue

This report dated 25 August 2020 has been prepared for Leicestershire County Council (the “Client”) in accordance with the terms and conditions of appointment (the “Appointment”) between the Client and Arcadis UK (“Arcadis”) for the purposes specified in the Appointment. For avoidance of doubt, no other person(s) may use or rely upon this report or its contents, and Arcadis accepts no responsibility for any such use or reliance thereon by any other third party.

CONTENTS

VERSION CONTROL ...... II

1 SUMMARY ...... 1

2 PROJECT SCOPE & CONTEXT ...... 2 2.1 Previous Investigations ...... 2 2.2 Scope of this Project ...... 2 2.3 Project Objective ...... 3 2.4 Data & Information ...... 3

3 MODEL BUILD ...... 4 3.1 Software ...... 4 3.2 Modelling Approach ...... 4 3.3 Feature Conceptualisation...... 4 3.4 Catchment Topography ...... 9 3.5 Modelling Assumptions & Limitations ...... 14

4 HYDROLOGY & RAINFALL ...... 15 4.1 Catchment Runoff ...... 15 4.2 Rainfall Events ...... 17

5 MODEL VALIDATION ...... 19 5.1 Historical Flooding ...... 19 5.2 EA Surface Water Flood Mapping ...... 22

6 FLOOD RISK ASSESSMENT ...... 24 6.1 Flooding Wetspots ...... 24 6.3 East Midlands Airport ...... 33

7 OPTIONS APPRAISAL ...... 37 7.1 Flood Mitigation Strategy ...... 37 7.2 Option Long-list ...... 37 7.3 Option Short-listing ...... 41 7.4 Promoted Options Evaluation ...... 44

8 ECONOMIC EVALUATION ...... 53 8.1 Overview ...... 53

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8.2 Scheme Costing ...... 53 8.3 Flood Benefits ...... 55 8.4 FCERM Funding ...... 56

9 FURTHER MITIGATION & CATCHMENT RESILIENCE ...... 57 9.1 Monitoring & Community Preparedness ...... 57 9.2 Adaptation & Re-purposing Strategies ...... 58 9.3 Natural Flood Management...... 59

10 CONCLUSIONS ...... 61 10.1 Flood Risk...... 61 10.2 Influence of the East Midlands Airport ...... 61 10.3 Options Feasibility ...... 61 10.4 Economic Viability ...... 61

...... 62 Data & Information Register ...... 62

...... 64 Watercourse Structures Register ...... 64

...... 71 2D Roughness Values ...... 71

...... 73 Flood Risk Mapping ...... 73

...... 88 Infiltration Parameters...... 88

...... 91 Diseworth – Property Level Resilience, Proposed Schedule...... 91

...... 95 East Midlands Airport Ponds Active Discharge Control – Technical Overview ...... 95

FIGURES Figure 1 – Example of Property Roof Runoff in the Model ...... 6 Figure 2 – Typical Connectivity of Highway Drainage System ...... 6 Figure 3 – East Midlands Airport Surface Water Model Subcatchments & Drainage Network ...... 7 Figure 4 – East Midlands Airport Ponds Layout and Interconnectivity (schematic) ...... 8 Figure 5 – East Midlands Airport Ponds Operating Regime (Schematic) ...... 9 Figure 6 – Demonstration of 2D Mesh Elements and Levels ...... 10 Figure 7 – Examples of Topographic 2D Meshing Detail ...... 10 Figure 8 – Topographic Adjustments to Buildings and Roads ...... 11 Figure 9 – Catchment Infiltration Characteristics ...... 12 Figure 10 – Catchment Runoff Approach Coverage ...... 15 Figure 11 – Westmeadow Brook Inflow Hydrograph Method Benchmarking ...... 17 Figure 12 – Critical Duration Assessment ...... 18 Figure 13 – EA RoFSW Flood Mapping Comparison ...... 22 Figure 14 – Wetspot Locations (showing 1 in 100 year flood depth) ...... 24 Figure 15 – Diseworth (Diseworth) Wetspot NRD Flood Predictions ...... 25 Figure 16 – Diseworth (Diseworth) Wetspot (showing 1 in 100 year flood depth) ...... 26 Figure 17 – Long Mere Lane (Diseworth) Wetspot NRD Flood Predictions ...... 27 Figure 18 – Long Mere Lane (Diseworth) Wetspot (showing 1 in 100 year flood depth) ...... 28 Figure 19 – Main Street (Long Whatton) Wetspot NRD Flood Predictions ...... 29 Figure 20 – Main Street (Long Whatton) Wetspot (showing 1 in 100 year flood depth) ...... 30 Figure 21 – Ashby Road (Long Whatton) Wetspot NRD Flood Predictions ...... 31 Figure 22 – Ashby Road (Long Whatton) Wetspot (showing 1 in 100 year flood depth) ...... 32 Figure 23 – East Midlands Airport, Predicted 1 in 20 year Pond Discharges due to Antecedent Rainfall ...... 33 Figure 24 – East Midlands Airport, Predicted 1 in 20 year Pond Discharges due to Rainfall Return Period .. 34 Figure 25 – Predicted 1 in 100-Year Flood Risk Impact in Diseworth from EMA Site Discharges ...... 36 Figure 26 – Long-list Options MCA Scores ...... 40 Figure 27 – Long-list Weighted Options Benefit Score ...... 40 Figure 28 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, General Arrangement ...... 45 Figure 29 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, NRD Flood Benefit ...... 46 Figure 30 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, 1 in 50-Year Flood Predictions ...... 47 Figure 31 – Main Street (Long Whatton) - Highway Re-Kerbing & Channel Works, General Arrangement 1 49

Figure 32 – Main Street (Long Whatton) - Highway Re-Kerbing & Channel Works, General Arrangement 2 49 Figure 33 – Main Street (Long Whatton) - Highway Re-Kerbing & Channel Works, NRD Flood Benefit ...... 50 Figure 34 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, 1 in 50-Year Flood Predictions ...... 51 Figure 35 – Economic Damage Figures ...... 56 Figure 36 – Recommended River Gauging Location ...... 58 Figure 37 – Diseworth (Diseworth) – East Midlands Airport Ponds Active Discharge Control, ENGINSOFT Digital Twin System ...... 97 Figure 38 – Diseworth (Diseworth) – East Midlands Airport Ponds Active Discharge Control, General Operational Architecture ...... 98

TABLES Table 1 – Infiltration Parameters ...... 13 Table 2 – Modelling Assumptions & Limitations ...... 14 Table 3 – Benchmarking Flood Predictions Against Flood History ...... 21 Table 4 – East Midlands Airport, Predicted 1 in 100 year Pond Discharges due to Antecedent Rainfall ...... 33 Table 5 – East Midlands Airport, Predicted 1 in 20 year Pond Discharges due to Rainfall Return Period ..... 34 Table 6 – Evaluation of Long-list Options ...... 39 Table 7 – Derivation of Short-list and Promoted Options ...... 43 Table 8 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, Predicted Percentage Contributions from M1 Runoff ...... 48 Table 9 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, Predicted Percentage Contributions from M1 Runoff ...... 52 Table 10 – Site Cost Assumptions ...... 54 Table 11 – Diseworth (Diseworth) - Property Level Resilience (PLR), CAPEX Cost Estimates ...... 54 Table 12 – Ashby Road (Long Whatton) – Bund & Flood Attenuation, CAPEX Cost Estimates ...... 54 Table 13 – Main Street (Long Whatton) - Highway Re-Kerbing & Channel Works, CAPEX Cost Estimates . 55

GLOSSARY

Abbreviation / Term Description

SWMP Surface Water Management Plan

Funding calculator for flood and coastal erosion risk management (FCRM) grant-in- FCERM GiA aid (GIA) allocation

SuDS Sustainable Urban Drainage System

PS Pumping Station

EA Environment Agency

OS Ordnance Survey

STW Severn Trent Water

NRD National Receptor Dataset

LiDAR Light Detection and Ranging digital ground data

CAPEX Capital Expenditure

OPEX Operational Expenditure

NPV Net Present Value

PF Partnership Funding

EMA East Midlands Airport

LWDPC Long Whatton and Diseworth Parish Council

vii

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

1 SUMMARY Between May 2013 and January 2014, Leicestershire County Council (LCC) commissioned URS Infrastructure & Environment UK Limited (URS) to undertake a desktop Catchment Study for Diseworth and Long Whatton1. This was a desktop study into flooding that has occurred in the villages of Long Whatton and Diseworth, and included the identification of prospective flood mechanisms and the proposal of outline mitigation measures. The study also provided a cursory consideration into the impact of runoff from the East Midlands Airport (EMA) flood risk within the catchment. Arcadis Consulting (UK) Limited were subsequently commissioned by LCC to further evaluate the flood mechanisms using a more empirical approach throughout the catchment, including the EMA surface water management system, and to appraise various flood mitigation options. If any viable options are identified a Flood and Coastal Erosion Risk Management Grant in Aid (FCERM GiA) Outline Business Case (OBC) would be developed to secure funding. This study required the development of a detailed 1D-2D hydraulic model of the catchment to provide enhanced resolution and confidence in the prediction of flood depths, extents, and mechanisms. To enable this a new high-resolution LiDAR survey and a watercourse survey was commissioned by LCC. The results of the modelling highlight that the primary causes of flooding in Diseworth are the limited conveyance capacity of the Diseworth Brook and lack of functional floodplain, due to historical encroachment. Discharge from the EMA drainage system are predicted to form a more major proportion of channel flow during lower return period events, but it’s impact diminishes as event return period increases owing to the effective attenuation capacity within the system. In Long Whatton, runoff from the rural upstream landscape and discharge from the M1 overwhelms culverts and surface water sewers in a couple of locations, resulting in flooding to properties. A couple of feasible options have been identified for Long Whatton which would provide attenuation and improved channel conveyance, significantly reducing flood risk for numerous properties in two locations. Preliminary design and costing have been undertaken, including the derivation of the necessary EA FCERM GiA funding figures. Through the course of the flood modelling study a range of options for mitigating flood risk have been tested for Diseworth, including evaluating options on both the Diseworth Brook and Hall Gate Brook. To date, a cost-effective option which is modelled to be successful has not been identified. Therefore, PLR measures have been proposed to help prevent properties from internally flooding. The Council has investigated other possible options that could provide any flood mitigation or improved resilience, such as:  Improved intelligence within existing water management systems  Early warning systems and CCTV  Reductions in peak volumes of water / slowing the flow, utilising Natural Flood Management (NFM) The options that have been explored are options that landowners have no legal obligation to implement. It is also important to note that the suggested options do not indicate that landowners are responsible for flooding or quick increases in flood flows.

1 https://www.leicestershire.gov.uk/sites/default/files/field/pdf/2019/2/11/diseworth-and-long-whatton- catchment-study.pdf

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

2 PROJECT SCOPE & CONTEXT 2.1 Previous Investigations 2.1.1 Catchment Study conducted by URS Infrastructure and Environment ltd (URS) (2014) The catchment study undertaken between May 2013 and January 2014 focused on what contribution of surface water runoff from the East Midlands Airport (EMA) may have on flood risk within the catchment. The main findings of the catchment study were:  “There are three separate sources of flooding from the Hall Brook, Diseworth Brook and from smaller watercourses upstream of Main Street, Long Whatton.”  “The EMA has a system that regulates surface water discharge rates from the site to the watercourses, which are agreed with the Environment Agency. As per the findings of the URS Catchment Study, EMA does not appear to have been a factor in flooding of Long Whatton and Diseworth in the 2012 event.”  “Surface water runoff from the surrounding catchment is thought to be the reason for the excess flows within the watercourses, due to the topography of the catchment and adjacent land uses.“ 2 2.1.2 Previous Consultations  2015.07.03 – Presentation to the EMA Independent Consultative Committee (ICC) on the EMA Water Management System along with the findings of the URS report, commissioned by LCC and published in January 2014  2015.07.24 – meeting attended by EMA, LCC, LWDPC, WINGS – where EMA shared the same presentation given to the ICC  2015.11.16 – meeting attended by EMA, LCC, LWDPC, WINGS  2016.06.24 – meeting attended by EMA, LCC, LWDPC  2016.10.22 – public meeting held at Diseworth Village Hall  2016.12.09 - meeting attended by EMA, LCC, LWDPC, WINGS, Hathern PC – discussed the options recommended at the end of the URS report  2017.06.30 - meeting attended by EMA, LCC, LWDPC, WINGS, Hathern PC – talked about funding options for a hydrological modelling (this study)  2018.05.23 - meeting and site tour of EMA water management system attended by EMA, LCC, LWDPC, NWLDC, WINGS, Hathern PC, Zouch Caravan park rep, and other residents  2018.08.06 – meeting EMA, LCC, LWDPC and two residents – study confirmed and funding agreed 2.2 Scope of this Project The scope is as follows:  Review all existing information, including any existing models, CCTV surveys, topographical surveys, LiDAR and previous reports to identify what further information is required to construct an InfoWorks ICM model  Where necessary, collect LiDAR, rainfall data, CCTV, and topographic survey data.

2 20180307 – Long Whatton and Diseworth Flood Study Tender Brief V3 Final

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

 Produce a new 1D-2D hydraulic model to simulate the performance of the catchment including all inflows from the EMA, the STW network and the surrounding area that flow into the catchment watercourses. The calibration and verification of the model against observed historic events.  Provide a baseline flood risk scenario both for ‘do nothing’ and also ‘do minimum’ scenarios. The baseline information is to be verifiable and robust in the event of challenges and should take into account the latest climate change guidance.  Production of a hydraulic modelling report in accordance with the relevant Environment Agency specification listing all assumptions, limitations, catchment descriptors and recommendations for any future additional work required.  Assess engineering and non-engineering solutions to reduce flood risk and provide wider environmental and ecological benefits and produce a short list of options to review with LCC and all relevant stakeholders.  Develop the ‘preferred’ scheme and undertake an outline design that can be tested in the model in line with: – The Environment Agency’s 5 case business model, – The Environment Agency’s Flood and Coastal Erosion Risk Management Appraisal Guidance and Funding Principles.  Produce cost estimates for the implementation of the preferred solution based on contemporary schemes of a similar nature.  Produce a Project Report that can be presented to the public detailing the findings of the hydraulic model and options appraisal. 2.3 Project Objective The objective of this project is to better understand the flood mechanisms throughout the catchment including the surface water management system of EMA and to appraise various flood mitigation options. The findings of the Flood Modelling Study will feed into the business case for the development of a potential flood mitigation scheme. The work should encompass the views of the local community and be conducted in partnership with all relevant Risk Management Authorities (RMA’s), professional bodies and stakeholders. 2.4 Data & Information A range of data sources have been used to provide network, hydraulic and catchment information to support the enhancement and validation of the model. The primary data sources have been listed in Appendix A.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

3 MODEL BUILD 3.1 Software The model has been developed using InfoWorks ICM (Integrated Catchment Modelling), a powerful integrated modelling platform that is able to represent fluvial networks, overland flows and sub- surface drainage within a fully integrated 1D-2D environment. An integrated model provides holistic and consistent hydraulic predictions based on the most up-to-date modelling techniques. The key benefits of InfoWorks ICM for this project are:  A flexible modelling environment, allowing tailored variation in model detail, resolution and schematisation to suit project needs that assists in the definition of topographic flow routes  A fully integrated simulation engine allowing the dynamic assessment of surface water and piped drainage systems that helps understand system interactions  Extensive interpolation and inference tools to aid the preparation of a consistent and robust representation of the urban drainage system, enabling the efficient enhancement of the model network and semi-automated interpolation where asset or survey data is not available  In-built flood analysis capability to create detailed visual representations of predicted flooding InfoWorks ICM integrates 1D and 2D hydrodynamic simulation techniques considering all flow paths enabling both the above-ground (surface flow paths, open channels and rivers) and below-ground (sewers, tanks, etc.) elements to be modelled together. InfoWorks ICM enables the hydraulics and hydrology of natural and man-made environments to be incorporated into a single model enabling the comprehensive, detailed and practical understanding of all aspects of natural runoff, engineered drainage systems and water management. 3.2 Modelling Approach Two models were built for the project using InfoWorks ICM in line with EA guidelines on fluvial modelling. The first, a 2D Runoff Model, to inform various parameters and modelling assumptions for the second, a 1D-2D System Runoff Model. 3.3 Feature Conceptualisation 3.3.1 Diseworth Brook / Long Whatton Brook A topographic river survey (undertaken by Storm Geomatics in 2018) of the Long Whatton Brook was undertaken collecting levels of the riverbanks, channel sections at regular intervals and dimensions and levels of culverts and structures. Channel sections were taken at approximately 100m intervals and where structures were identified. Each channel section contained XYZ data along with a surface type which was given a Manning’s roughness value3. Regular interval topographic points were also collected on both riverbanks. The channel sections were imported into the model to form cross sections for the 1D river network and the bank points were used to create bank lines for interaction of flow between 1D and 2D environments. The model cross-sections were cropped to the tops of the riverbanks where necessary and linked to the 2D surface created from a DTM.

3 Chow, V.T. (1959) Open Channel Hydraulics. McGraw-Hill, New York.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

The survey included information and diagrams of any structures along the watercourse. These were added to the 1D river reach and further details of each can be found in the structures register in Appendix B. Culvert inlet and outlet records4 have been used to ensure accurate predictions of culvert headloss based on photos and the site familiarisation walkover survey. During the representation of watercourse culverts, bridges and structures, reference was made to the information collated in the URS report and site photos. 3.3.2 Minor Tributaries & Land Drainage Minor tributaries and land drains were modelled within the 2D rather than the 1D for improved detail and reduced chances of instabilities arising between the 1D and 2D. Mesh level zones5 were used where the ground model was insufficient to capture minor drainage features. Depending on the drainage feature in question the ground level would either be lowered manually or interpolated between known points. 3.3.3 Piped Drainage Networks 3.3.3.1 Surface Water Sewers Records from STW provided the majority of the surface water sewer network. The InfoWorks built- in inference tool was used to fill in any missing invert levels and dimensions in the records along with any information gathered during site visits. 3.3.3.2 Combined Sewers Combined sewer network digital GIS data from Severn Trent Water (STW) was provided covering the whole catchment. The InfoWorks built-in inference tool was used to fill in any missing invert levels and dimensions in the records. Subcatchments were created on a property basis using MasterMap data with an occupancy of 2.4 assumed per dwelling and drained to the appropriate combined node. 3.3.4 Property Roof Runoff Property roof runoff was modelled using defined subcatchments with explicit connections to the appropriate network. Building outlines were taken from MasterMap data to form the subcatchments and the whole roof area of each building was included in runoff. A graphical demonstration of the subcatchment creation process can be seen in Figure 1.

4 InfoWorks ICM network links used to specify the inlet and outlet losses for a culvert, as defined in the Culvert Design Manual (1997) published by CIRIA. 5 Mesh Level Zone objects are used as part of the 2D mesh generation process in InfoWorks ICM, used to modify Mesh Elements based on ground level elevations or user-defined values

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Figure 1 – Example of Property Roof Runoff in the Model 3.3.5 Road Drainage (excluding M1 & A42) A complete representation of the road drainage system has been included, based on gully data location information by LCC. A set of standard assumptions have been made to replicate a ‘typical’ highway drainage system, as shown below:  Gully grate dimensions (m)= 0.4 x 0.5  Cross slope (m/m) = 0.01  % clogging = 30%  Gully pot depth (m) = 0.3  Gully pot area (m2) = 0.2 There is insufficient information available to confirm the specific connectivity of individual gullies (i.e. discharged via in-line rider sewers or directly piped laterals to the adjacent sewer) so each gully has been connected to the nearest manhole on the appropriate drainage system. Gullies have been connected to the surface water system except where only a combined sewer is present in the road. A pipe diameter of 150mm has been assumed to connect gullies to the sewers. Figure 2 shows a typical layout.

Legend Gully Assumed gully lateral connection Surface water sewers / manholes Foul sewers / manholes

Figure 2 – Typical Connectivity of Highway Drainage System

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

3.3.6 M1 & A42 The M1 and A42 drainage has been included in the model based on information taken from LiDAR and MasterMap data. As no engineering drawings of the drainage network were available, the road network has been modelled as subcatchments draining to one another based on the gradient of the road (taken from LiDAR). Where the subcatchments converge at a low spot, they would discharge to the 2D surface via a conduit. The runoff for the M1 & A42 subcatchments was defined using the OS MasterMap land use data. Two runoff surfaces were used, an impermeable runoff surface to mimic the highway itself, and a permeable runoff surface to represent the verges. An area take-off was carried out using the land use data to split the total subcatchment area into the two runoff surfaces. Engineering drawings were provided for some of the watercourse culverts which pass under the two highways and the information from these was included in the model. 3.3.7 East Midlands Airport The surface water drainage network for the East Midlands Airport (EMA) has been included in the model. Site drainage drawings of the network were provided by EMA which were digitised in the model. These included some pipe diameters and invert levels; all remaining levels and diameters were inferred using InfoWorks’ inference tools. Runoff from the EMA was modelled in 1D using subcatchments draining to the network. The EMA provided information on the surface water catchments of the site which is shown in Figure 3.

Figure 3 – East Midlands Airport Surface Water Model Subcatchments & Drainage Network 3.3.7.1 Storage Ponds The majority of the surface water network drains by gravity to a series of ponds/reservoirs to the south of the site. These ponds are in place to allow the EMA to regulate their surface water discharges to ensure that the de-icing compound they use on their runways does not contaminate local watercourses. There are six ponds on the site (two in each location), as below:  Eastern Ponds  Central Ponds  Western Ponds The connectivity of the ponds to each other and their discharge locations is shown in Figure 4.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Figure 4 – East Midlands Airport Ponds Layout and Interconnectivity (schematic)

The ponds were modelled using storage nodes (which define a level-area relationship) with reference to information from engineering drawings provided by EMA. Their operating regime is outlined in detail in the EMA Description of Operation document6, which provided the necessary information to replicate the basic pumping regime and define the capacity of discharge controls in the model. This was supplemented by verbal confirmation of key aspects of the operation by EMA staff during a site walkover survey. The general operating regime is shown in Figure 5. Some information necessary to complete the model representation that was not readily available from the documentation or drawings had to be derived based on the following assumptions:  The geometry and profile of the discharge channel from the Eastern Ponds, which runs behind the Jury’s Inn East Midlands Airport was assumed based on site observations and LiDAR data  The overflow channel and pond downstream of the Central Ponds was assumed based on site observations and LiDAR data  The connectivity of piped drainage leading from the EMA Short Stay Car Park area under the A453 and discharging into the Hall Brook was assumed based on local topography and drainage records obtained from EMA  Unknown pipe dimensions and levels within the EMA site were interpolated from adjacent pipework, aiming to maintain consistency of diameter

6 Description of Operation - East Midlands Airport (P65827-Doo-Misc-H), 06/03/2018 (Rev 8)

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Figure 5 – East Midlands Airport Ponds Operating Regime (Schematic) 3.4 Catchment Topography 3.4.1 Digital Terrain Model A DTM was developed using 50cm LiDAR data procured by LCC for the extent of the 2D model as the opensource EA LiDAR data provided insufficient coverage. 3.4.2 2D Surface A 2D surface in InfoWorks ICM is generated from the DTM as a 2D Mesh, which is an irregular grid of contiguous 2D Elements. This mesh is comprised of individual triangular 2D Elements of varying sizes, smaller adjacent triangle elements can be merged into a single element if needed to meet the target resolution. Each 2D Element is initially assigned a ground level that is calculated as an average of all the DTM spot levels that fall within it. The 2D Mesh was created based on the DTM data as outlined in Section 3.4.3. The sizes of the 2D Elements have been tailored to provide a balance between the prediction of precise overland flows and duration of model simulations. 2D element sizes in rural areas more distant from Long Whatton and Diseworth are typically larger, up to 1,000m2. Roads, urban paved surfaces and private gardens within Long Whatton and Diseworth have smaller 2D Element sizes, with a maximum of 5m2, to improve model resolution in these more critical locations. 2D Elements are allowed to drop down to 2m2 where this is necessary to represent small topographic features, such as alleyways or narrow pavements.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

DTM Data Derived 2D Mesh & Levels

Figure 6 – Demonstration of 2D Mesh Elements and Levels 3.4.3 Land Use & Topographic Features The OS MasterMap data has been used to define land type and topographic detail, forming the building blocks for precise and dynamic 2D meshing that accounts for the nature of the catchment. The polygon data enables the definition of spatially varying surface parameters, 2D Element size, terrain complexity and adjustments to account for specific urban features, such as road kerbs. The inclusion of this detail also helps to prevent over-estimation of flood risk and damages. Each building is defined by a single 2D Element. A demonstration of the use of OS MasterMap to create topographical detail within the 2D mesh can be seen in Figure 7 The OS MasterMap classification data has been used to define varying surface roughness (e.g. to differentiate between vegetated and paved areas) and infiltration parameters (i.e. permeable vs impermeable), as outlined in 3.4.4.

Enhanced 2D Mesh Including OS MasterMap Basic 2D Mesh Topographic Definition Showing a random mesh of relatively similarly sized 2D Showing the building footprints and other topographical elements features used to define variable sized 2D Elements

Figure 7 – Examples of Topographic 2D Meshing Detail

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

3.4.3.1 Buildings & Roads Mesh Zones are used to adjust various properties of the 2D Elements based upon their location. Mesh Zones have been used to:  Raise the 2D Elements representing buildings to 150mm above the surrounding ground level (DTM), unless determined as being different through observation. This represents typical ground floor threshold levels to avoid the over-estimation of property flood risk and to ensure building structures can impede shallow overland flows  Reduce the level of the 2D Elements representing roads by 100mm. The resolution of the DTM is not sufficient to provide an accurate definition of road kerb edges, which can significantly impact overland flow routing A graphical representation of these adjustments is shown in Figure 8.

Building footprint (+150mm) Road footprint (-100mm)

Ground level (LiDAR)

Cross-section Example Plan Showing Adjustments

Figure 8 – Topographic Adjustments to Buildings and Roads 3.4.3.2 Ponds (Not EMA Ponds) A number of permanent water features (natural and man-made detention ponds) are located throughout the catchment. All these features have been included in the model and have been represented in the 2D mesh using Mesh Zones and, where necessary, Mesh Level Zones to define their banks. The Mesh Zones define a static water level derived from the EA LiDAR data, considered to represent a ‘typical’ water level. The meshing size has been defined to ensure that each pond is only defined by a single element. 3.4.4 Surface Parameters The OS MasterMap data has been used to define spatially varying infiltration and roughness values, based on classification data and industry standard values. 3.4.4.1 Roughness The Manning’s n roughness figures, as defined by Chow (1959), have been used across the catchment. The typical values have been applied based on the OS MasterMap land use classification and have been summarised in Appendix C.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

3.4.4.2 Infiltration Infiltration has been applied to the 2D Mesh using Infiltration Zones7, applying specified infiltration as a constant rate to each 2D Mesh Element. National Soil Map data was referenced8 to identify the spatial variation of soil type, allocated into the four Soil Classification system (SCS) groups9.

Soilscapes map Model Infiltration Zones

Legend

Slightly acid loamy and clayey soils with impeded SCS Soil Group A (low runoff potential and high drainage infiltration rates even when thoroughly wetted) Slowly permeable seasonally wet slightly acid but SCS Soil Group B (moderate infiltration rate when base-rich loamy and clayey soils thoroughly wetted and consists chiefly or moderately Freely draining slightly acid loamy soils deep to deep, moderately well to well drained soils) Loamy and clayey floodplain soils with naturally high SCS Soil Group C (low infiltration rates when groundwater thoroughly wetted and consist chiefly of soils with a layer that impedes downward movement of water) SCS Soil Group D (very low infiltration rates when thoroughly wetted)

Figure 9 – Catchment Infiltration Characteristics

A nominal 95% runoff coefficient has been included to account for un-modelled surface interception storage (i.e. 5% loss of rainfall retained in-situ). The Horton method has been to model infiltration as it allows for the replication of varying infiltration rates during rainfall events, accounting for varying catchment saturation. The Horton Limiting rate defines how low infiltration can drop during rainfall and is considered to represent the minimum effective infiltration. The InfoWorks recommended Horton values are included in Table 1.

7 Infiltration Zone objects are used to apply infiltration parameters to the 2D Mesh 8 Cranfield Soil and Agrifood Institute Soilscapes map (http://www.landis.org.uk/soilscapes/) 9 Soils are classified by the Natural Resource Conservation Service into four Hydrologic Soil Groups based on the soil's runoff potential. The four Hydrologic Soils Groups are A, B, C and D. Where A's generally have the smallest runoff potential and Ds the greatest.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

SCS Soil Group A SCS Soil Group B SCS Soil Group C SCS Soil Group D

Moderately low runoff Moderately high runoff Low runoff potential, High runoff potential, potential, comprised potential, comprising Description largely comprised of comprising greater of loamy sand, silt and of a significant sand and gravel than 40% clay some clay proportion clay

f0 (mm.hour) 250 200 125 75

fc (mm.hour) 25.4 12.7 6.3 2.5

K (1/hour) 2 2 2 2

Table 1 – Infiltration Parameters

The recommended values were then combined with OS MasterMap land use data to take into account the permeability of different land uses as well as the appropriate soil conditions. The final infiltration parameters used in the model are in Appendix E.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study 3.5 Modelling Assumptions & Limitations All key modelling assumptions and associated limitations have been outlined in Table 2.

Type Assumption(s) Limitation(s) Impact(s) on Predictions Future Mitigation(s)

Some gullies may have been omitted, reducing the capacity to discharge surface water into the public Network The highway drainage system in Long Whatton and sewers Minor increase in surface water depths and During detailed design the model should be updated Dimensions & Diseworth has been based on manually digitised corresponding reduction in volume discharged to Any restrictions due to hydraulic capacity or blockages with information collected during any topo surveys Connectivity locations and interpolated connectivity within the connecting lateral pipes (i.e. between the drainage network gullies and public sewers) cannot be evaluated within the model

M1 and A42 drainage connections have been The lack of detail around connectivity and levels assumed – All paved areas and cutting slopes have The inclusion of 100% of the paved and cutting slopes Connectivity reduces confidence in flow and depth predictions - been assumed to effectively drain to the relevant is considered conservative within the M1/A52 drainage system watercourse / land drainage channel

All property roofs in Long Whatton and Diseworth have Some roofs may discharge to local soakaways, Connectivity been assumed to be connected to the nearby - creating an overestimation of runoff entering the - appropriate system. surface water system

Sedimentation within all pipes has been assumed based on gradient and pipe diameter, to ensure a During detailed design it is recommended that CCTV conservative representation of likely capacity. No information available to clarify the assumed Condition - surveys be conducted for any critical sections of the Sediment has been included in all pipes with a sediment levels applied to the model drainage network, and the model updated gradient less than 1 in 100, scaled up to 20% of pipe height for pipes with a gradient of 1 in 10 or higher

Design rainfall falls consistently over the entire Rainfall - Creates a conservative estimation of rainfall runoff - catchment

No flood prediction along the M1/A42 will be generated Used 1D subcatchments to represent runoff from the using this model. Any residual flooding predicted within Runoff & Flooding - - M1/A42, instead of the 2D Mesh the M1/A42 will have originated from outside of the M1/A42 and should be discounted

A dedicated study to derive typical soil permeability at The runoff model roughness and infiltration rates are An under/over prediction in the upstream catchment key locations across the catchment would provide Runoff simplified and based on the downstream catchment - inflows into the model could influence predicted flood valuable data to re-calibrate the model, if considered characteristics results in the main model. necessary

Table 2 – Modelling Assumptions & Limitations

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

4 HYDROLOGY & RAINFALL 4.1 Catchment Runoff A combined approach to the generation of catchment runoff has been employed, utilising the following two approaches:  2D Direct rainfall runoff – covering the watershed of the Diseworth Brook / Long Whatton Brook catchment  Inflow Hydrographs – accounting for runoff from the Westmeadow Brook The application (coverage) of these two approaches is shown is Figure 10.

Diseworth

2D Direct Rainfall Long Whatton Runoff Area

Inflow location

Upstream Non-2D Direct Rainfall Runoff Catchment

Figure 10 – Catchment Runoff Approach Coverage

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

4.1.1 Direct Rainfall Generated Runoff The direct rainfall runoff capability of InfoWorks ICM enables the dynamic simulation of natural runoff, accounting for topography, variable surface roughness, ground infiltration and physical features which can affect overland flows. This approach provides dynamic and linked hydraulic and hydrological predictions, reducing the reliance on the derivation of statistical inflows and providing a detailed understanding of overland connectivity. 4.1.1.1 Saturation & Initial Conditions A 30% initial ground saturation level has been assumed for design events, included to account for the likely occurrence of a period of rainfall prior to an ‘extreme’ rainfall event. This value was selected to define a typical wetness but limited to ensure design events do not over-predict runoff. The EMA ponds were set to 80% full (based on total capacity below the overflow weir crest levels). This value was selected to represent a pragmatic assumption of the EMA drainage system discharging runoff from the period of prior rainfall, but not being at full capacity. 4.1.2 Westmeadow Brook Inflow Hydrographs Two approaches were tested for the derivation of inflow hydrographs:  ReFH2 inflows hydrographs  2D direct rainfall runoff derived inflow hydrographs The ReFH2 inflows were generated using Revitalised Flood Hydrograph software (version 2.2) according to industry standard best practice. Inflows were generated for a range of durations and for a range of return periods. The peak flow rate and runoff volume for a range of 1 in 100-year design events durations, as derived by these two methods, have been generated and compared in Figure 11. The comparison demonstrates that the direct rainfall runoff method generates significantly higher peak flow rates than the ReFH2 method. Runoff volumes with ReFH2 are higher during longer durations but are generally comparable at durations matching the 2D direct rainfall runoff peak flow rates. Based on this assessment the use of 2D direct rainfall runoff is considered the more conservative approach, aligning with the use of 2D direct rainfall runoff for the main catchment and focusing the evaluation of risk around event severity.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

45 800,000

40 700,000

35 600,000 30 500,000 25 400,000 20

300,000 (m3) Volume

Peak Flow (m3/s) Flow Peak 15 200,000 10

5 100,000

0 0 0 500 1,000 1,500 2,000 2,500 Event Duration (mins)

Figure 11 – Westmeadow Brook Inflow Hydrograph Method Benchmarking

Legend:

ReFH2 Flow (m3/s) ReFH2 Volume (m3)> 0.2m ICM Direct Rainfall Runoff Model Flow (m3/s) ICM Direct Rainfall Runoff Model Volume (m3) 4.2 Rainfall Events 4.2.1 Design Events The following FEH design events were created to both provide a broad understanding of flood risk and align with the general requirements of the FCERM GiA process:  1 in 5-year event  1 in 20-year event  1 in 50-year event  1 in 75-year event  1 in 100-year event 4.2.2 Critical Duration Assessment A single critical event duration was identified based on the evaluation of three metrics, generated using a range of durations for a 1 in 100-year event. The results are shown in Figure 12.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

180 700 3.00 160 600 2.50 140 500 120 2.00 100 400 1.50 80 300 60 1.00 200 (m) Depth 40 Area of floodwater (ha) floodwater of Area 100 0.50 20 No. of properties flooding properties of No. 0 0 0.00 60 120 240 360 720 1440 2880 60 120 240 360 720 14402880 Duration (mins) Duration (mins)

No. of properties flooding Peak flood depth (m) Area of Floodwater (ha)

Figure 12 – Critical Duration Assessment

Model predictions indicate that a shorter and more ‘flashy’ rainfall duration creates the largest net level of risk, across all three metrics. A 60-minute duration has subsequently been selected for this study.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study 5 MODEL VALIDATION 5.1 Historical Flooding There have been several flooding incidents over the last few years in both Long Whatton and Diseworth, providing useful direct evidence of flood extents and depths. A critical comparison of model predictions against flood evidence is shown in Table 3.

Location / Dates Images / Evidence Model Predictions Validation Comments

The photographic and descriptive evidence10 of 1 in 20 Year Event flooding show a positive match with both predictions of flood depth and extent. It was remarked that flooding entered the property form the Crawshaw Close, front and rear, mimicked by Long Whatton the flood predictions (2019 / 2020) A/B (discussed further in 6.1.4.3). The grass verge along the western side of Crawshaw close is shown to be ‘dry’ in both the model predictions A B and photo A, adding confidence to flood depths.

10 https://www.bbc.co.uk/news/av/uk-england-leicestershire-50427534/water-floods-homes-in-long-whatton / https://www.bbc.co.uk/news/uk-england- leicestershire-50837034

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study Location / Dates Images / Evidence Model Predictions Validation Comments

1 in 50-Year Event

The flood predictions show a good correlation to depth and Shakepeare Drive, extent in this location, Diseworth (2018) although there is a lack of photographic evidence of the wider flood extent.

Numerous photographs have been obtained showing high water levels in the Diseworth Brook at Lady Gate Bridge (at bridge soffit) and highway flooding.

Lady Gate Road B The model predictions indicate Bridge, Diseworth that this area would be A (2019) susceptible to regular inundation from highway runoff, unable to effectively drain due to high river levels. The correlation of model 1 in 20-Year Event predictions with photographic A B evidence is considered good.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study Location / Dates Images / Evidence Model Predictions Validation Comments

Flooding along the footpath and the footbridge is predicted Lady Gate B to occur during frequent (footbridge), rainfall events, matching the Diseworth (2017) photographic and reported A evidence well.

1 in 20-Year Event

Elevated water levels along this section are replicated in Rear Gardens of B the model but appear slightly Brookside, suppressed. This is Diseworth (2000 / A considered the result of a 2012) miss-match in local LiDAR levels.

1 in 20-Year Event

Table 3 – Benchmarking Flood Predictions Against Flood History

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

The property adjacent to the Hall Gate road bridge has also reported high water levels within the brook upstream of the bridge, impacting their garden. The model predictions correlate relatively well. Confidence in the capacity of the road bridge is limited due to lack of structural information. 5.2 EA Surface Water Flood Mapping A comparison of flood extent and depth with the EA RoSFW mapping is shown in Figure 13.

Model Predictions (1 in 100-year Event)

EA RoFSW

Figure 13 – EA RoFSW Flood Mapping Comparison

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

The model predictions clearly indicate that the general flood extent being greater than the EA RoFSW mapping, especially downstream of Diseworth, around Long Mere Lane (Diseworth), along the floodplain to the north of Long Whatton, and along the Westmeadow Brook. The difference is primarily attributed to the inclusion of various culverts within the upstream catchment (i.e. across the A42/M1, connecting field drainage channels etc.) which increased its conveyance and prevented the accumulation of floodwater behind artificial landscape features. This provide confidence that the model is conservative and generates predictions that reflect the scale of known risks in the catchment (as discussed in 5.1).

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

6 FLOOD RISK ASSESSMENT 6.1 Flooding Wetspots 6.1.1 Summary Due to the spatial distribution of Department for Environment, Food and Rural Affairs (DEFRA) National Receptors Dataset (NRD) points along the valley it was necessary to split the catchment into ‘wetspots’, defined based on common flood mechanisms affecting clusters of NRD properties. The defined wetspots are as follows, and as shown in Figure 14:  Diseworth Village (Diseworth)  Long Mere Lane (Diseworth)  Main Street (Long Whatton)  Ashby Road (Long Whatton)

Diseworth (Diseworth)

Long Mere Lane (Diseworth)

Main Street (Long Whatton)

Ashby Road (Long Whatton)

Figure 14 – Wetspot Locations (showing 1 in 100 year flood depth)

Legend:

Flood Depth NRD Property Flooding < 0.1m > 0.1m > 0.2m > 0.3m > 0.5m > 0.75m > 1.0m > 2m

The specific risk and flood mechanisms for each Wetspot are outlined in Sections 6.1.2 to 6.1.5.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

6.1.2 Diseworth 6.1.2.1 NRD Flood Impact The calculated risk to properties identified on the NRD register are summarised in Figure 15, split between property count and depth statistics. There is an observable threshold at 1 in 50-years where risk rapidly increases, representing the effective capacity of the Diseworth Brook (and its immediate local floodplain) being reached. This does demonstrate that the extent of flood risk (specifically internal property flooding) is relatively limited during the more frequent events. This is partially corroborated by photographic evidence of high-water levels inundating garden areas but not directly flooding properties. Predicted flood depth follows a far more linear trend as the return period increases.

16 0.5 14 0.45 0.4 12 0.35 10 0.3 8 0.25 6 0.2 0.15 4

0.1 (m) Depth Flood NRD 2 No NRD Properties Flooded Properties NRD No 0.05 0 0 0 10 20 30 40 50 60 70 80 90 100 Event Return Period (yrs)

NRD Flood Risk Av NRD Flood Depth Max NRD Flood Depth

Figure 15 – Diseworth (Diseworth) Wetspot NRD Flood Predictions 6.1.2.2 Flood Extent & Depth The majority of flooding in Diseworth is directly caused high water levels in the Diseworth Brook, with flooding occurring along the whole length (excluding the culverted section). The main areas that floodwater accumulates are as follows:  Hall Gate (adj. to Linthwaite Close) – extensive flooding of the carriageway to a depth that would prevent emergency access, local gardens and some properties  Shakespeare Drive – extensive flooding of local gardens, properties and a pedestrian footway  Along the banks of the Hall Gate Brook – minor flooding along the banks, affecting some adjacent properties and their gardens  Land to the east of the confluence of the Hall Gate Brook and Diseworth Brook – extensive and deep flooding of low-lying land, functioning as a surrogate floodplain  Rear Gardens of Brookside Close and Lady Gate – Extensive shallow flooding which inundates gardens and some properties  Multiple locations along Lady Gate – combination of floodwaters from the Diseworth Brook and surface water flooding, significant enough to potentially affect emergency access The flood predictions for the 1 in 100-year event are shown in Figure 16, while the full set of flood risk maps can be seen in Appendix D.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Figure 16 – Diseworth (Diseworth) Wetspot (showing 1 in 100 year flood depth)

Legend:

Flood Depth NRD Property Flooding < 0.1m > 0.1m > 0.2m > 0.3m > 0.5m > 0.75m > 1.0m > 2m 6.1.2.3 Flood Mechanisms The source of flooding is relatively well known and historically documented, originating from the Diseworth Brook. The model predictions provide an empirical demonstration that the primary mechanisms of flooding can be described as follows:  Limited conveyance capacity along the length of the Diseworth Brook (as it passes through Diseworth), primarily due to its constrained and variable cross-sectional area, and undergrown encroachment  Lack of functional floodplain caused by historical encroachment of properties gardens and pedestrian footways, resulting in elevated floodwater depths  Suspected raised profiling of the rear gardens of some properties in Brookside (during their construction) which retains watercourse flows within bank around the tight corner as it passes under the footbridge (Lady Gate), contributing to raised water levels upstream A cursory review of historical mapping (circa 1937-1961) underpins the assertion that loss of functional floodplain is a major risk factor. Nine of the 15 properties predicted to be at risk of flooding during a 1 in 100-year event have been constructed since 1961. Most of these property gardens encroach on the existing watercourse bank alignment and contribute to elevating flood risk. The various road and footbridges in Diseworth are not predicted to have an influential impact on flooding. Floodwaters are predicted to navigate around these structures once their effective capacity has been reached.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

6.1.3 Long Mere Lane (Diseworth) 6.1.3.1 NRD Flood Impact The calculated risk to properties identified on the NRD register are summarised in Figure 17, split between property count and depth statistics. The risk to NRD properties steadily increased from the 1 in 20-year event, with depths increasing at in a relatively linear trend. The number of properties plateaus at four since there are no other NRD properties within this general area. Confidence in the depth predictions is inhibited by the inherent uncertainty in defining ‘thresholds’ for farm buildings, relevant for two of the four properties at risk. One property called ‘Tea Kettle Hall’ in the NRD dataset attributes, to the east of Long Mere Lane within closed private land, has been demolished, rendering any economic damages void.

5 0.3

4 0.25 0.2 3 0.15 2 0.1

1 0.05 (m) Depth Flood NRD No NRD Properties Flooded Properties NRD No 0 0 0 10 20 30 40 50 60 70 80 90 100 Event Return Period (yrs)

NRD Flood Risk Av NRD Flood Depth Max NRD Flood Depth

Figure 17 – Long Mere Lane (Diseworth) Wetspot NRD Flood Predictions 6.1.3.2 Flood Extent & Depth Floodwaters, which largely originate from the land drainage channel, which routes runoff from farmland to the southwest, discharge into Long Mere Lane before inundating the adjacent scrubland and The Green. Floodwaters continue northeast, once crossing The Green, and into farmland before discharging into the Diseworth Brook. The main areas that floodwater accumulates are as follows:  Long Mere Lane (adj. to the farm buildings) – Deep flooding along the roads and within surrounding fields, affecting one of the farm buildings  Within the closed private land (old car park) – Floodwaters accumulate within the footprint of the old carpark, retained by the bounding earth walls  Farm Buildings (north of The Green) – affected by flooding from Long Mere Lane which flows over The Green and through these farm buildings on its route to the Diseworth Brook The flood predictions for the 1 in 100-year event are shown in Figure 18, while the full set of flood risk maps can be seen in Appendix D.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Figure 18 – Long Mere Lane (Diseworth) Wetspot (showing 1 in 100 year flood depth)

Legend:

Flood Depth NRD Property Flooding < 0.1m > 0.1m > 0.2m > 0.3m > 0.5m > 0.75m > 1.0m > 2m 6.1.3.3 Flood Mechanisms There are no documented occurrences of flooding here, but evidence of minor surface water flooding was found during the site walkover survey (i.e. accumulated debris along road). The model predictions provide an empirical demonstration that the primary mechanism of flooding is the significant rural runoff from the upstream catchment, which overwhelms the land drainage channel and downstream drainage networks 6.1.4 Main Street (Long Whatton) 6.1.4.1 NRD Flood Impact The calculated risk to properties identified on the NRD register are summarised in Figure 19, split between property count and depth statistics. The risk to NRD receptors increases rapidly from the 1 in 5-year to the 1 in 20-year events, rising steadily before plateauing at the 1 in 75-year event. This indicates that local properties are sensitive to internal flooding at relatively low floodwater depths (i.e. 0.1 m to 0.3 m average depths). The local topography and evidence of flooding recently provides a demonstration of this sensitivity, generating confidence in the profile shown in Figure 19.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

14 0.5 0.45 12 0.4 10 0.35 8 0.3 0.25 6 0.2 4 0.15

0.1 (m) Depth Flood NRD 2

No NRD Properties Flooded Properties NRD No 0.05 0 0 0 10 20 30 40 50 60 70 80 90 100 Event Return Period (yrs)

NRD Flood Risk Av NRD Flood Depth Max NRD Flood Depth

Figure 19 – Main Street (Long Whatton) Wetspot NRD Flood Predictions 6.1.4.2 Flood Extent & Depth The floodwaters predicted in this area represent the relatively wide conveyance route, following the topographic ‘valley’ which passes directly through properties along Crawshaw Close. Flood depths are general restricted to the 0.2 m to 0.3 m range on average, since the downstream landform enables floodwater to be continually conveyed into the Long Whatton Brook. Floodwaters collect in the rear gardens of properties along Crawshaw Close to more significant depths, as they are set slightly lower than the surrounding made ground levels. The flood predictions for the 1 in 100-year event are shown in Figure 20, while the full set of flood risk maps can be seen in Appendix D.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Figure 20 – Main Street (Long Whatton) Wetspot (showing 1 in 100 year flood depth)

Legend:

Flood Depth NRD Property Flooding < 0.1m > 0.1m > 0.2m > 0.3m > 0.5m > 0.75m > 1.0m > 2m 6.1.4.3 Flood Mechanisms Flooding in this area is well documented, with several recent events occurring and used to aid the validation of the model (See Section 5.1). The culvert under Main Street and the drainage channel alongside Crawshaw Close provide the primary route to convey all agricultural runoff (including runoff from a section of the M1) from the catchment to the southwest under Main Street, and on into the Long Whatton Brook. The central influencing factor is that the current drainage infrastructure does not have the capacity to convey flows past Main Street. The model predictions provide an empirical demonstration that the primary mechanisms of flooding can be described as follows:  Road kerbs and local elevation prevents surface water on the highway effectively discharging to the drainage channel alongside Crawshaw Close

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

 Properties along Crawshaw Close sit within a natural depression with the road set slightly higher forming, a physical barrier which prevents runoff draining away and exacerbating depths and risk 6.1.5 Ashby Road (Long Whatton) 6.1.5.1 NRD Flood Impact The calculated risk to properties identified on the NRD register are summarised in Figure 21, split between property count and depth statistics. The risk to NRD receptors increases rapidly from the 1 in 5-year to the 1 in 20-year events, rising steadily before plateauing at the 1 in 75-year event. This indicates that local properties are sensitive to internal flooding at relatively low floodwater depths (i.e. 0.1 m to 0.2 m average depths).

9 0.3 8 0.25 7 6 0.2 5 0.15 4 3 0.1 2 0.05 (m) Depth Flood NRD

No NRD Properties Flooded Properties NRD No 1 0 0 0 10 20 30 40 50 60 70 80 90 100 Event Return Period (yrs)

NRD Flood Risk Av NRD Flood Depth Max NRD Flood Depth

Figure 21 – Ashby Road (Long Whatton) Wetspot NRD Flood Predictions 6.1.5.2 Flood Extent & Depth The model predictions demonstrate that runoff from local fields and the highway tend to accumulate and flow down what appears to be the natural valley bottom, which runs through properties on Turvey Lane. Flood depths are general restricted to the 0.1 m to 0.3 m range on average, only deepening when restricted by structures such as buildings. The flood predictions for the 1 in 100-year event are shown in Figure 22, while the full set of flood risk maps can be seen in Appendix D.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Figure 22 – Ashby Road (Long Whatton) Wetspot (showing 1 in 100 year flood depth)

Note: The NRD point outlined is considered anomolous and is not included in the graphed results in Figure 21 and the economic calculations (See Section 8)

Legend:

Flood Depth NRD Property Flooding < 0.1m > 0.1m > 0.2m > 0.3m > 0.5m > 0.75m > 1.0m > 2m 6.1.5.3 Flood Mechanisms Flooding is largely driven by the magnitude of runoff from agricultural land and discharges from the M1 during extreme rainfall overwhelming the natural drainage channels down Ashby Road. The culverts along Ashby Road which convey drainage channel flow through the urban area are considered proportionate but are unable to cope with more extreme rainfall. Larger culverts would not resolve the issue since upstream catchment runoff that spreads out laterally into adjacent fields is unable to effectively discharge back into the drainage channels, before they are culverted.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

6.2 East Midlands Airport Although the risk assessment simulations were based on the assumption that the ponds were 80% full prior to the commencement of rainfall (as stated in 4.1.1.1) sensitivity testing has also been undertaken. This aim of these tests was to extrapolate the range of discharges rates (and volumes) that would be expected to occur from the EMA ponds when considering different periods of prior rainfall (referred to as ‘antecedent conditions’). The model was run with varying initial water levels to replicate differing antecedent conditions, the results of which are shown in the following sections. 6.2.1 Pond Discharge Assessment Three antecedent pond capacity conditions have been evaluated in Table 4 and Figure 23.

Antecedent Peak Flow Rate (m3/s) Total Discharge Volume (m3) Pond Capacity* Western Central Eastern Total Western Central Eastern Total

100% 0.4 0.5 0.7 1.6 20,500 13,450 51,200 85,200

50% 1.4 0.5 0.8 2.7 71,050 15,000 58,500 144,500

20% 1.5 0.8 0.9 3.2 70,750 18,650 63,900 153,100

Table 4 – East Midlands Airport, Predicted 1 in 100 year Pond Discharges due to Antecedent Rainfall

* Value indicates percentage of pond capacity full prior to start of rainfall (based on total capacity below the overflow weir crest levels)

4.00 200,000 /s) 3 3.50 150,000 ) 3 3.00 100,000 50,000 2.50 0 2.00 -50,000 1.50 -100,000 1.00 -150,000 Peak Discharge Rate (mRate Discharge Peak Discharge Volume (m Volume Discharge 0.50 -200,000 - -250,000 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Antecedent Pond Capacity

Figure 23 – East Midlands Airport, Predicted 1 in 20 year Pond Discharges due to Antecedent Rainfall

Legend:

Flood Depth Peak Discharge Rate (polynomial trend line) Total Discharge Volume (polynomial trend line)

The assessment indicates that peak discharges steadily increase as antecedent pond capacity decreases, but does not exceed a maximum rate of 3.5 m3/s. The volume also increases (as would

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study be expected) but the rate of increase is much less than that of flow, effectively reaching a plateau at approximately 150,000 m3. 6.2.2 Return Period Assessment Three antecedent pond capacity conditions have been evaluated in Table 5 and Figure 24.

Peak Flow Rate (m3/s) Total Discharge Volume (m3) Return Period 100% 50% 20% 100% 50% 20%

1 in 5 year 0.3 0.6 0.7 42,650 103,300 109,100

1 in 20 year 0.3 0.8 0.9 55,850 116,830 123,700

1 in 100 year 0.4 1.4 1.5 85,200 144,500 153,100

Table 5 – East Midlands Airport, Predicted 1 in 20 year Pond Discharges due to Rainfall Return Period

* Value indicates percentage of pond capacity full prior to start of rainfall (based on total capacity below the overflow weir crest levels)

1.6

1.4 /s) 3 1.2

1.0

0.8

0.6

0.4

Peak Discharge Rate (m Rate Discharge Peak 0.2

0.0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Anteceedent Pond Capacity Figure 24 – East Midlands Airport, Predicted 1 in 20 year Pond Discharges due to Rainfall Return Period

Legend:

Peak discharge rate (m3/s) from the EMA ponds 1 in 5 Year Event 1 in 20 Year Event 1 in 100 Year Event

The assessment shows that for dryer antecedent conditions with the ponds largely empty (i.e. 20%) the discharge rate is comparable across all return periods. As the pond capacity decreases the peak flow rate rapidly increases, then levelling out once capacity has reduced to around 50%. This plateau in the data indicates that the EMA drainage infrastructure provides ‘buffering’, suppressing higher intensity events through in-system storage, the ponds themselves and the continual transfer of flows to the largest Western Ponds (and on to the River Trent).

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

6.2.3 Flood Risk Impact The model confirms that whilst discharges from the EMA site are predicted to elevate flood risk in Diseworth, largely through flows down the Hall Gate Brook from the Eastern Ponds, the general extent and depth of flooding remains largely unchanged (as can be seen in Figure 25). The predicted 1 in 100-year flood depth at the property adjacent to the Hall Gate Brook of 0.2m could potentially be reduced to < 0.05m with no discharge from the Eastern Ponds occurring. However, predicted peak flood depth at properties downstream along the Diseworth Brook could only be reduced by < 0.1m on average. Although discharges from the EMA site can constitute from approximately 5% to 20% of the total flow in the Diseworth Brook (depending on the severity of rainfall) the effective capacity that the drainage infrastructure provides incidental flood risk protection. To quantify this benefit a scenario was developed in the model to ‘remove’ the EMA site. This was achieved by removing all piped infrastructure and the topographic depression made by the ponds within the DTM. The land use parameters where adjusted to replicate the land being largely rural, mimicking the characteristics of the wider catchment. The results (as shown in Figure 25) demonstrate that with the EMA site drainage infrastructure an additional eight properties would potentially be at risk (i.e. 73% increase) while flood depths would substantially increase. Several other properties further downstream in Long Whatton would also be directly at risk. This indicates that the drainage infrastructure (i.e. ponds and pipes) provides a relatively significant level of incidental flood protection. This is not only provided by the operating capacity of the ponds but also the effective storage within the 35km+ of piped drainage network, totalling approximately 11,500m3 of capacity. It is important to note that the representation of the topography of a pre-EMA site in the model is highly simplistic. There have been large areas of earthworks and re-profiling undertaken during the airport’s history, for many of which it has not been possible to revise due to a lack of reference information. The results are only considered indicative.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Baseline Model

No Discharges from the EMA Site

No-EMA Site (i.e. pre-development)

Figure 25 – Predicted 1 in 100-Year Flood Risk Impact in Diseworth from EMA Site Discharges

Legend:

Flood Depth NRD Property Flooding < 0.1m > 0.1m > 0.2m > 0.3m > 0.5m > 0.75m > 1.0m > 2m

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

7 OPTIONS APPRAISAL 7.1 Flood Mitigation Strategy The approach to identifying affordable and cost-beneficial options to mitigation flood risk and support a business case for funding has been based on the following factors:  Projected extent of flood benefit - focusing on addressing clusters of NRD properties  Projected magnitude of flood benefit – reducing the frequency of NRD property flooding  Proportional affordability – achieving a balance between engineering effort and projected flood benefit  Wetspot representation – focus on the wetspots with the greatest perceived community concerns / recent flood history, All five wetspots are hydraulically discrete from one another, each with their own key mechanisms and influences. Accordingly, there are no common options which could be developed to maximum catchment-wide benefit. The economic viability of each proposed option will be considered independent. 7.2 Option Long-list The long-list has been proposed for each Wetspot, formulated by considering a wide range of technical approaches within the concept of the sustainable drainage hierarchy (source-pathway- receptor), aiming to maximise resilience and the selection of more cost-beneficial options. The identification of measures has considered suggestions from local residents (through public consultations) and Parish Council members. It has been established that control at source (i.e. NFM measures or equivalent) are unlikely to generate the necessary economic benefit to justify national funding (i.e. FCERM GiA). The anticipated extent of investment required to substantially reduce peak flows would be disproportionate to the relatively small number of NRD properties at risk. However, such measures could attract regional or local investors, and have been specifically considered in Section 9.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study 7.2.1 Multi-Criteria-Assessment Overview All options identified as conceptually applicable to this catchment have been identified and critically reviewed against a range of technical, environmental and social key attributes, enabling a more robust and inclusive assessment of projected benefit. This multi-criteria-assessment (MCA) is presented in Figure 26.

Multi-Criteria-Analysis

No NRD Properties Projected Option Wetspot to Benefit Option Design & Function Primary Constraints Feasibility Affordability Flood Mitigation Environmenta l Impact Amenity Take Land Community Acceptance Sustainability Resilience

Construction of an artificial wetlands area alongside the Diseworth Brook with the fields adjacent to Hall Gate,  Land purchase / loss of functional Hall Gate Community northwest of Diseworth. The design would include at least two agricultural land Attenuation Basin / Diseworth Village 10 stages, the higher stage(s) providing floodwater attenuation Wetlands  Challenging ecological engineering and a shared community park space (during dry weather required conditions).

Provision of arrange of property level resilience measures (inc. Property Level flood walls, flood doors, flood proof wall treatments and  Feasibility (property age constraints) Diseworth Village 11 Resilience (PLR) pumps) for properties at risk (and neighbouring properties,  Property owner engagement / support subject to site surveys).

Upstream Construction of flood bunds alongside the Diseworth Brook to  Land purchase / loss of functional Watercourse Diseworth Village 14 the southwest of Diseworth to create a flood attenuation within agricultural land Attenuation Basin agricultural land, typically used for livestock  Does not influence runoff from EMA

Hall Brook Construction of a 1.5 km long new channel that would divert  Landowner engagement / land Watercourse Bypass Diseworth Village 11* the majority of flows within the Hall Brook around to the east of purchase Channel Diseworth Brook.  Projected high cost

 Technically complex Targeted structural remedial works along the Diseworth Brook Watercourse (within Diseworth) to increase channel capacity (inc. widening,  Property owner / landowner Encroachment Diseworth Village 14 channel straightening and replacement of bridges, and engagement / support Reversal Works culverts)  Limited projected flood mitigation benefit

Increase in storage capacity the EMA Ponds through the  Lack of available land within EMA site East Midlands Airport extension of the existing ponds or construction of new Ponds Capacity Diseworth Village 15  High cost of excavation material balancing ponds, either within EMA land or immediately Increase disposal downstream  Projected high cost

 Technically complex  Property owner / landowner Diseworth Brook Construction of a low-level culvert connection from the engagement / support Eastern Culvert Diseworth Village 10 Diseworth Brook (around the Brookside area), discharging Bypass around 200m downstream back into the Diseworth Brook  Projected High Cost  Clashes with existing sewerage / utilities

Re-alignment of approx. 1km of the Diseworth Brook downstream of Diseworth, aligning the route with the predicted  Landowner engagement / support floodwaters at a 0.5-1.0 m lower elevation. Downstream  Projected High Cost Watercourse Re- Diseworth Village 14 The option would aim to reduce top water levels immediately alignment downstream of Diseworth (at the Lady Gate road bridge),  Limited flood risk benefit reducing peak water levels within Diseworth and mitigating the  Long-term maintenance requirements severity of flooding.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study Multi-Criteria-Analysis

 Property owner / landowner engagement / support Construction of a new surface water sewer and highway New Piped Drainage Long Mere Road 4 drainage infrastructure, routing runoff under The Green, and System  Projected high cost into the Diseworth Brook.  Limited projected flood mitigation benefit

 Sewer conflict with existing sewers / Construction of a flood bund within the field to the rear of utilities Flood Bund Ashby Road 6 Turvey Lane  Land purchase / loss of functional agricultural land

 Sewer conflict with existing sewers / Flood Bund & Construction of a flood bund within the field to the rear of utilities Ashby Road 6 Attenuation Turvey Lane and local excavations to maximse capacity  Land purchase / loss of functional agricultural land

Provision of arrange of property level resilience measures (inc. Property Level  Feasibility (property age constraints) Ashby Road 6 flood doors and flood proof wall treatments) for properties at Resilience (PLR) risk (and neighbouring properties, subject to site surveys).  Property owner engagement / support

Construction of a flood bund within the field to the rear of  Land purchase / loss of functional Flood Bund & Road Ashby Road 6 Turvey Lane and the re-profiling (lowering) of Ashby Road to agricultural land Re-profiling route flows through urban area.  Projected cost of highway works

Re-profiling of Main Street from the church down to Crawshaw  Maintaining local resident parking Highway Re-Kerbing Close to prevent surface water flowing down Mill Lane, then Main Street 12 availability & Channel Works discharged into an improved channel alongside Crawshaw

Close.  Projected cost of highway works

Main Street  Limited projected flood mitigation Creation of a natural flood storage area upstream of the M1 benefit M1 Attenuation Basin 9 culvert, utilising an appropriate flow control mechanism  Not feasible to include a high-level overflow

Main Street  Would require significant earthworks, Main Street Flood Creation of a flood attenuation area alongside Main Street, plus disposal costs 12 Attenuation Area adjacent to Crawshaw Close.  Land purchase / loss of functional livestock land

Table 6 – Evaluation of Long-list Options

Note: * Three properties discounted (See Section 7.4.1)

Legend:

High / Positive Impact (score = +1) Medium / Neutral Impact (score = 0) Low / Negative Impact (score = -1) * Options sorted based on the Net Score (high to low)

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study 7.2.2 Multi-Criteria-Assessment Results The net long-list MCA scores (as shown in the legend for Table 6) are presented in Figure 26.

10 0

8 10

6 20

4 30 2 40 0 MCA Score MCA

50 to Benefit Projected Propoerties NRD No. -2 Negative MCA scores -4 shown in black 60

-6 70 Diseworth - Main Street - Main Street - Diseworth - Ashby Road - Main Street - Ashby Road - Diseworth - Diseworth - Diseworth - Diseworth - Diseworth - Long Mere Ashby Road - Main Street - Diseworth - Property Level Highway Re- Flood Diseworth Flood Bund Flood Bund & Property Level Hall Brook East Midlands Upstream Downstream Hall Gate Lane - New Flood Bund & M1 Watercourse Resilience (PLR) profiling & Attenuation Brook Eastern Attenuation Resilience (PLR) Watercourse Airport Ponds Watercourse Watercourse Community Piped Drainage Road Re- Attenuation Encroachment Channel Works Area Culvert Bypass Bypass Channel Capacity Attenuation Re-alignment Attention Basin System profiling Basin Reversal Works Increase Basin / Wetlands

Figure 26 – Long-list Options MCA Scores

Note: sorted left to right based on the Weighted Options Benefit Score shown in Figure 27

To provide a direct comparative analysis a ‘Weighted Option Benefit Score’ has been derived, calculated as the average MCA score multiplied by the number of NRD properties projected to benefit. The resulting values have been normalised (from 0% to 100% for easy reference), presented in Figure 27.

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% Weighted Option Benefit Score Benefit Option Weighted 0% Diseworth - Main Street - Main Street - Diseworth - Ashby Road - Main Street - Ashby Road - Diseworth - Diseworth - Diseworth - Diseworth - Diseworth - Long Mere Ashby Road - Main Street - Diseworth - Property Level Highway Re- Flood Diseworth Flood Bund Flood Bund & Property Level Hall Brook East Midlands Upstream Downstream Hall Gate Lane - New Flood Bund & M1 Watercourse Resilience (PLR) profiling & Attenuation Brook Eastern Attenuation Resilience (PLR) Watercourse Airport Ponds Watercourse Watercourse Community Piped Drainage Road Re- Attenuation Encroachment Channel Works Area Culvert Bypass Bypass Channel Capacity Attenuation Re-alignment Attention Basin System profiling Basin Reversal Works Increase Basin / Wetlands

Figure 27 – Long-list Weighted Options Benefit Score

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study 7.3 Option Short-listing All options defined in the Long-List (See Section 7.2), following their MCA appraisal, have undergone critical review to establish a Short-List and set of ‘Promoted’ options, which have been more thoroughly and technically evaluated (using the model where appropriate) and costed in Section 8.2. This review process aimed to identify those options considered deliverable and effective (in terms of flood risk mitigation), in relation to their expected cost and technical complexity. The steps in this process and justifications for progressing each option through the stages is outlined in Table 7.

Option Wetspot No NRD Average Pre-Evaluation Discounted Option (inc. justification) Preliminary Evaluation Evaluation Outcome / Recommendation Options Promoted Properties MCA Score Undertaken for Preliminary Projected Hydraulic to Benefit Evaluation

Hall Gate Community Diseworth Village 10 0.5 Discounted None - No Attenuation Basin / The anticipated technical complexity and cost associated with land Wetlands purchases / long-term maintenance likely to inhibit the development of a cost-beneficial solution, whilst also not addressing flows from Hall Gate and local runoff downstream

Property Level Diseworth Village 11 2.5 Considered for Preliminary Evaluation Extraction of predicted top Relatively low peak depths indicate that PLR is Yes Resilience (PLR) water levels for the 1 in likely to be applicable and technically feasible. 100-year event for the

identification of suitable

PLR measures

Upstream Diseworth Village 14 0.5 Considered for Preliminary Evaluation Simple representation of The option could potentially prevent flooding at No Watercourse flood attenuation bund site of the 15 NRD properties at risk, plus Attenuation Basin tested with a 1 in 100-year minor flood depth improvements (<= 0.1m).

event The option would require the construction of a 225m long bund up to 3.5m high in places, including a new access road for maintenance. An indicative CAPEX estimation based on EA evidence indicates that such a scheme would cost a minimum of approx. £1m, which would not generate sufficient FCERM GiA funding.

Hall Brook Diseworth Village 11 1 Considered for Preliminary Evaluation High-level technical The option would be technically feasible to No Watercourse Bypass feasibility assessment construct. The extent of the required works Channel undertaken to ascertain (approx. 1.5km) and associated costs is not

whether the local likely to generate a suitable return on topographic and drop in investment, considering it’s benefit would not elevation (between the extent all properties at risk in Diseworth and EMA and Diseworth Brook) would not address rural runoff from the would be sufficient southern and western areas slopes which drain to the Diseworth Brook.

Watercourse Diseworth Village 14 -2 Discounted None - No Encroachment The expected investment, technical complexity and limited flood risk Reversal Works benefit is low (as shown by the low MCA score)

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study Option Wetspot No NRD Average Pre-Evaluation Discounted Option (inc. justification) Preliminary Evaluation Evaluation Outcome / Recommendation Options Promoted Properties MCA Score Undertaken for Preliminary Projected Hydraulic to Benefit Evaluation

East Midlands Airport Diseworth Village 15 0.5 Discounted None - No Ponds Capacity Limited flood risk benefit associated with the expected scale of Increase investment / technical complexity

Diseworth Brook Diseworth Village 10 1.5 Considered for Preliminary Evaluation Two potential routes for a Both culvert locations demonstrate that No Eastern Culvert bypass culvert through sufficient peak flows can be passed out of Bypass Diseworth have evaluated Diseworth but their actual rate of is inhibited by

using the model, based on high water levels downstream of Diseworth a culvert sized to (backwater), severely restricting the effective accommodate peak 1 in flood benefit. 100-year flows once out of bank flooding is predicted to occur

Downstream Diseworth Village 14 0.5 Discounted None - No Watercourse Re- Significant extent of excavations required for relatively limited hydraulic alignment benefit, due to the slack local gradients within farmland downstream of Diseworth

New Piped Drainage Long Mere Road 4 1 Discounted None - No System The expected investment required to construct a buried solution is not considered proportionate to address widespread flooding for only four NRD locations, only one of which could be considered a sensitive structure (See Section 6.1.3.1)

Flood Bund Ashby Road 6 2.5 Considered for Preliminary Evaluation Scheme feasibility The construction would require material at No (see next option) determined to be relatively cost, which reduces the overall return on positive (reflected in the investment – more effective source of material

MCA score). Desktop (cut from attenuation basin) considered more review of potential bund pragmatic locations and material requirement

Flood Bund & Ashby Road 6 2.5 Considered for Preliminary Evaluation Simple representation of a This approach could provide flood protection Yes Attenuation flood bund and excavated for the majority of NRD flood receptors up to area behind developing the 1 in 100-year event, with a basic

and tested in the model for earthworks intervention and minor inlet culvert the 1 in 100-year event improvements

Property Level Ashby Road 6 2 Discounted None - No Resilience (PLR) The route of the predicted floodwater (via rear gardens) and predicted velocities would require major PLR measures to be installed, potentially affecting access and land usage, potentially inflating installation costs

Flood Bund & Road Ashby Road 6 0.5 Discounted None - No Re-profiling Re-profiling works would require significant highway interruptions along a major route (with limited diversion options), plus anticipated issues with depth of cover to existing infrastructure and local resident accesses. The relatively slack road gradient indicates that a major change in gradient (necessary to substantially improve the conveyance of overland away from the areas of flooding) would be topographically difficult

Highway Re-Kerbing Main Street 12 2 Considered for Preliminary Evaluation No preliminary modelling Option to be evaluated in full Yes & Channel Works has been undertaken – this option is considered the

only practical option to improve local conveyance and is likely to significantly reduce flood risk to 12 NRD receptors

M1 Attenuation Basin Main Street 9 -0.5 Discounted None - No The distance upstream (relatively small contributing catchment) and technical complexity / liability of utilising the M1 embankment to create a floodwater attenuation basin severely limits the likely return on investment and scale of actual flood risk mitigation.

Main Street Flood Main Street 12 1.5 Considered for Preliminary Evaluation A review of the local The required attenuation volume necessary to No Attenuation Area landform and predicted reduce flood risk to an acceptable level is overland flow routes has significant and could not be provided within the

been undertaken to available space without major earthworks, establish the technical which would render the land largely unusable feasibility and likely scale for its existing or other purposes (i.e. livestock / of this option equestrian)

Table 7 – Derivation of Short-list and Promoted Options

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

7.4 Promoted Options Evaluation 7.4.1 Diseworth (Diseworth) - Property Level Resilience (PLR) The predicted depths of flooding for most properties in Diseworth up to the 1 in 100-year event are limited to approximately 0.3 m. Given this, an investment in PLR is considered a cost-beneficial and practical approach to provide flood protection, given the significant projected cost and complexity constraints associated with of undertaking major engineering works within Diseworth. Of the 15 properties predicted to be at risk (See Section 6.1.2.1), three are new builds (2019) and would not quality for FCERM GiA funding, and one property (Shakespeare Dr) is already protected by PLR. The remaining 11 properties could potentially benefit from PLR. Option Design & Implementation An indicative schedule of properties evaluated based on model predictions to be ‘at-risk’ (i.e. <= 0.5m flood depth and no existing known flood defence measures), for which PLR is recommended, was formulated to enable indicative costing. A site schedule will need to be developed based on more detailed site investigations (i.e. threshold level surveys). The type and age of these properties, and their immediate neighbours, is relatively diverse. This implies that appropriate topographic and structural surveys should be conducted to ensure that PLR is considered for all relevant properties, addressing the inherent uncertainty in flood modelling and the LiDAR data used. Funding & Delivery Property-level protection can be funded through the EA FCERM GiA under Outcome Measure 2, if evaluated to move properties from the very significant (i.e. < 1 in 20 years) to a higher risk category. Since no properties are predicted to quality (Figure 15) alternative sources of funding would be required. 7.4.2 Ashby Road (Long Whatton) – Bund & Flood Attenuation The land behind properties along Turvey Lane provides opportunity to construct a flood bund, directly protecting those properties and other immediately downstream, largely by deflecting the overland flow path into the drainage channel along Ashby Road. The extensive space in the field and local topography would also enable minor excavations and profiling to provide attenuation volume behind the bund, maximising benefit and limiting incidentally increases in flood depth and flow rate within the carriageway of Ashby Road. A couple of addition bunds have been proposed to maximise property protection and increaser general scheme resilience. Option Design & Implementation The structural components / works are as follows:  Primary flood bund (50.5m AOD or higher) – earthen bund set just behind the rear gardens of properties along Turvey Lane, tied into the natural ground level to the north and west, surrounding the re-constructed culvert inlet  Lateral flood bund (approximately 50.0m AOD) – minor earthen bund within the Ashby Road verge alongside No. 66 Turvey Lane  Supplemental flood bund (at least 0.5m above the general ground level) - minor earthen bund along the western boundary of the electricity sub-station access road.  Flood attenuation area - set at a general level of 48.5mAOD with batter slopes that tie in with the 49.5mAOD contour

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

 Re-constructed culvert inlet structure – located on the drainage channel shifted within the flood storage area, to include trash screen and maintenance access  Realignment of the drainage channel – diversion of flows directly into the flood attenuation area, to ensure out-of-bank flooding is retained behind the flood bund and routed more efficiently into the re-constructed culvert inlet structure The general arrangement proposed is shown in Figure 28.

Primary flood bund

Lateral flood bund Flood attenuation area

Drainage channel realignment

Re-constructed culvert inlet Supplementary Flood bund structure

Figure 28 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, General Arrangement

To maximise benefit, support construction works and minimise costs, a number of design considerations / recommendations are proposed:  The design should seek to limit any earth cut disposal by using it in constructing the three bunds on site  Within the flood attention area, a series of French drains should be laid to enable effective drainage of saturated ground and local groundwater  Providing a reinforced high-level overflow section within the flood bund (adjacent to the culvert inlet), set approximately 0.5 m below the primary flood bund crest level Hydraulic & Flood Risk Evaluation The option has been run against the full set of design storm events to enable a direct comparison of flood mitigation benefit against the Do Minimum predictions. The model indicates that this option would substantially reduce the risk to local properties, reducing the frequency of flooding from 1 in 20-years to 1 in 100-years and limiting peak flood depths to 0.05 m. The reduction in flood risk to local NRD receptors is demonstrated in Figure 29.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

9 0.3

8 0.25 7

6 0.2

5 0.15 4

3 0.1 NRD Flood Depth (m) Depth Flood NRD

No NRD Properties Flooded Properties NRD No 2 0.05 1

0 0 0 10 20 30 40 50 60 70 80 90 100 Event Return Period (yrs) Figure 29 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, NRD Flood Benefit

Legend:

Do Minimum Option

No. NRD Properties Flooded Maximum Flood Depth Average Flood Depth

The option effectively retains floodwaters behind the primary bund while the attenuation area provides sufficient capacity to prevent any increase to floodwater along Ashby Road downstream. The model predictions for the 1 in 50-year event is are shown in Figure 30.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Baseline (Do Minimum) Option

Figure 30 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, 1 in 50-Year Flood Predictions

Legend:

Flood Depth NRD Property Flooding < 0.1m > 0.1m > 0.2m > 0.3m > 0.5m > 0.75m > 1.0m > 2m Funding & Delivery This option would be entitled to FCERM GiA funding and may be eligible for local levy funding from the Trent Regional Flood and Coastal Committee. Securing funding from private sources should be maximised where influence on risk can be effectively demonstrated. Additional funding could be sought from Highways England under their responsibility managing and operating the M1 which intersects the catchment upstream. Within their Road Investment Strategy they have a Designated Fund Programme to address key challenges. Their Environmental Fund includes ‘Flooding and Water Quality’ as one of its seven key areas. To be considered for funding the works must meet a number of criteria, the primary ones related to this option being:  Identify capital works either on our estate, or which have a clear relationship with it  Result in a measurable improvement in the network’s environmental performance  Maximise opportunities for joint funding or partnership The predicted peak runoff rates and volumes from the M1 have been compared to predictions of flow passing through the Ashby Road Wetspot area, shown in Table 8.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Metric 5 yr 20 yr 50 yr 75 yr 100 yr

Volume 23% 10% 10% 9% 8%

Peak Flow 11% 4% 3% 3% 3%

Average 17% 7% 6% 6% 5%

Table 8 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, Predicted Percentage Contributions from M1 Runoff 7.4.3 Main Street (Long Whatton) - Highway Re-Kerbing & Channel Works The existence of a formalised land drainage channel running immediately adjacent to the majority of properties at risk in Crawshaw Close provides the opportunity to maximise the value of an existing ‘asset’, through refurbishment. This option would aim to improve the connectivity of local road surfaces and collected floodwaters with the drainage channel along Crawshaw Close. This would be achieved through construction of a new pavement and kerb to specifically retain floodwaters within Main Street, preventing runoff into Mill Lane, before enabling its efficient discharge into the drainage channel. Additional proprietary channel remediation and widening works will also be required to maximise the conveyance capacity of the drainage channel. Although it is recognised that increasing the capacity of the road culvert would be pragmatic it would only provide minor improvement during more frequent rainfall events, and would have limited effect during more severe and economically damaging events. Option Design & Implementation The structural components / works are as follows:  Construct 25m of new pavement and raised kerb along Main Street – kerb profile should maintain a level approximately 0.2 m higher than the current ground level  Re-build 20m of existing pavement – grading the profile of the new pavement and raised kerb into the existing pavement (at the location of the existing speed table in Crawshaw Close)  Construct a new speed table at the junction with Mill Lane – profiled flush with the pavements either side to prevent water flowing into Mill Lane  Drainage channel remediation / widening – depending on the detailed design works should be included the re-formalise the channel, including maintaining longitudinal capacity (i.e. removing any pinch points), adding stabilisation where necessary, and re-profiling the bed  Construction of a highway runoff spillway – removal of kerbs to create an at-grade spillway and apron into the drainage channel

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Channel remediation & widening

Highway runoff spillway (through pavement) New / re-built pavements with raised kerbs

Speed table

Figure 31 – Main Street (Long Whatton) - Highway Re-Kerbing & Channel Works, General Arrangement 1

The details of the recommended road works are shown in Figure 32.

Highway runoff spillway (through pavement)

Speed table

Re-built existing New pavement with pavement raised kerbs

Figure 32 – Main Street (Long Whatton) - Highway Re-Kerbing & Channel Works, General Arrangement 2

A key design and feasibility consideration will be the potential impact on the historic Manor farmhouse and outbuildings (No. 77 Main Street) that works on the channel may have, designated as grade II listed buildings. Works in the channel may undermine structural stability while an increasing in the ‘wetting’ of the local ground may cause water damage. A watertight wall structure may need to be considered running alongside the existing wall to minimise risk, sensitivity designed to be integrated into the current building aesthetics and architectural style.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Hydraulic & Flood Risk Evaluation The option has been run against the full set of design storm events to enable a direct comparison of flood mitigation benefit against the Do Minimum predictions. The model indicates that this option would substantially reduce the risk to local properties, reducing the frequency of flooding from 1 in 20-years to 1 in 100-years and reducing peak flood depth from 0.45 m to 0.1 m for the 1 in 100-year event. The relatively low depths of residual flooding could be addressed by the inclusion of supplementary PLR measures (not included in the costing). The reduction in flood risk to local NRD receptors is demonstrated in Figure 33.

14 0.5 0.45 12 0.4 10 0.35 0.3 8 0.25 6 0.2

4 0.15 NRD Flood Depth (m) Depth Flood NRD 0.1 No NRD Properties Flooded Properties NRD No 2 0.05 0 0 0 10 20 30 40 50 60 70 80 90 100 Event Return Period (yrs) Figure 33 – Main Street (Long Whatton) - Highway Re-Kerbing & Channel Works, NRD Flood Benefit

Legend:

Do Minimum Option

No. NRD Properties Flooded Maximum Flood Depth Average Flood Depth

The model predictions demonstrate that the road re-profiling routes undrained highway runoff along Main Street into the drainage channel along Crawshaw Close as proposed, preventing any runoff flowing down Mill Lane. The model predictions for the 1 in 50-year event is are shown in Figure 34.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Baseline (Do Minimum) Option

Figure 34 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, 1 in 50-Year Flood Predictions

Legend:

Flood Depth NRD Property Flooding < 0.1m > 0.1m > 0.2m > 0.3m > 0.5m > 0.75m > 1.0m > 2m Funding & Delivery This option would be entitled to FCERM GiA funding, and may be eligible for local levy funding from the Trent Regional Flood and Coastal Committee. Securing funding from private sources should be maximise where influence on risk can be effectively demonstrated. Additional funding could be sought from Highways England under their responsibility managing and operating the M1 which intersects the catchment upstream. Within their Road Investment Strategy they have a Designated Fund Programme to address key challenges. Their Environmental Fund includes ‘Flooding and Water Quality’ as one of its seven key areas. To be considered for funding the works must meet a number of criteria, the primary ones related to this option being:  Identify capital works either on our estate, or which have a clear relationship with it  Result in a measurable improvement in the network’s environmental performance  Maximise opportunities for joint funding or partnership

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

The predicted peak runoff rates and volumes from the M1 have been compared to predictions of flow passing through the Ashby Road Wetspot area, shown in Table 9.

Metric 5 yr 20 yr 50 yr 75 yr 100 yr

Volume 128% 29% 24% 21% 19%

Peak Flow 95% 19% 11% 9% 8%

Average 112% 24% 18% 15% 14%

Table 9 – Ashby Road (Long Whatton) – Bund & Flood Attenuation Option, Predicted Percentage Contributions from M1 Runoff

The 1 in 5-year event results appear anomalous due to a lack of detailed topographic and land drainage information at the upstream inlet of the M1 culvert, located upstream of this Wetspot. These values should be discounted for this assessment.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

8 ECONOMIC EVALUATION 8.1 Overview The evaluation of economic viability has been undertaken based on a 100-year overall design life, as agreed with LCC during consultations. 8.2 Scheme Costing 8.2.1 CAPEX Costs 8.2.1.1 Cost Inventory An inventory of Capital Expenditure (CAPEX) Costs has been collated from standard industry assumptions and related project examples, covering all components of the preliminary design. Information was drawn from numerous sources, including:  SPONS Civil Engineering and Highway Works Price Book (2018)  SPONS External Works and Landscape Price Book (2018)  SPONS Architects and Builders Price Book (2018)  South West Water S104 Cost Estimation (Capital works cost evaluation inventory for infrastructure investment)  CIRIA (2007)  Stovin & Swan (2007)  EA FCERM Cost Estimation Guidance Where a component type references multiple cost estimates, a range has been derived. Within the cost estimation calculation, the unit cost for each component has been defined based on a minimum, maximum or average cost value, depending on confidence and / or uncertainty. All CAPEX costs within the inventory have been adjusted for inflation since the dates of specification, based on UK Government annual inflation rate data covering the last 20 years. 8.2.1.2 Site Costs The estimated site costs have been derived from typical industry standards and experience, drawing from numerous water and wastewater infrastructure project examples. The values derived (and used to evaluate the scheme cost) are averages of the expected full range of values typically associated with a project of this type. A schedule of site cost assumptions is shown in Table 10.

Item Min Max Average Comments

Design Costs 8% 12.5% 10% % of total CAPEX cost

Client Overheads 5% 7.5% 6.3% % of total CAPEX cost

Highways Notices / 2.5% 5% 3.8% % of total CAPEX cost Estates Costs

Contractor Mobilisation 10% 15% 12.5% % of total CAPEX cost and Preliminaries

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Item Min Max Average Comments

Utility Diversions £82.40 £169.14 £125.77 Based on small pipe lay (per m)

Contingency 5.0% 7.5% 6.3% % of total CAPEX cost

Table 10 – Site Cost Assumptions 8.2.1.3 Diseworth (Diseworth) - Property Level Resilience (PLR) An indicate estimate of CAPEX cost to cover the installation of PLR measures for the 11 identified properties is shown in Table 11, derived from figures in Appendix F.

Survey Total CAPEX Admin Total Cost Site Est. Costs Cost Est. Costs

Total £63,640 £7,296 £70,936 £12,728 £83,664

Total +60% bias £101,824 £11,674 £113,498 £20,365 £133,862

Table 11 – Diseworth (Diseworth) - Property Level Resilience (PLR), CAPEX Cost Estimates

These cost estimates are based on the 11 identified properties identified in the modelling as highest risk and should be considered estimates at the time of writing, subject to change following site investigation surveys and property owner consultations. 8.2.1.4 Ashby Road (Long Whatton) – Bund & Flood Attenuation An itemised CAPEX cost schedule is shown in Table 12.

Option Est. Base Adj. Adjustment Total Unit Cost Component Quantity CAPEX Inflation Factor CAPEX

Attenuation Area 3,500 m3 £13 £43,880 £53,250 -25% £40,675

Channel Excavation 25 m £305 £7,625 £9,425 - £9,425

Channel Dredging 50 m £27 £5,965 £7,370 -25% £5,525

Soft Bank 125 m £30 £3,750 - £4,635 £4,635 reinforcement

Culvert Extension 10 m £1,400 £14,000 £17,305 - £17,305

Culvert Inlet 1 £3,750 £3,755 +25% £5,800 £4,640 Structure

Total £83,365

Total +60% bias £133,384

Table 12 – Ashby Road (Long Whatton) – Bund & Flood Attenuation, CAPEX Cost Estimates

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

8.2.1.5 Main Street (Long Whatton) - Highway Re-Kerbing & Channel Works An itemised CAPEX cost schedule is shown in Table 13.

Option Est. Base Adj. Adjustment Total Unit Cost Component Quantity CAPEX Inflation Factor CAPEX

Pavement Works 40 m £25 £1,770 £1,880 +25% £2,350

Speed Table 1 £10,000 £10,000 £10,170 +50% £15,255

Edge Posts 20 £20 £360 £390 - £390

Fence 50 m £25 £1,150 £1,190 - £1,190

Channel Excavation 130 m £50 £6,500 £8,035 - £8,035

Hard Bank 75 m £25 £1,950 £2,410 - £2,410 reinforcement

Total £29,630

Total +60% bias £47,408

Table 13 – Main Street (Long Whatton) - Highway Re-Kerbing & Channel Works, CAPEX Cost Estimates 8.3 Flood Benefits 8.3.1 Evaluation of Flood Damages Property damages were calculated using the MCM depth damage data from the 2014 Multi-coloured Handbook (Flood Hazard Research Centre, 2014). A conservative approach was adopted and depth-damage data without basements was used in the assessment. Flood depths for individual properties were extracted using a point analysis of the model predictions. Property Damages were capped if present value damages exceeded property market values. Property annual average damages were calculated, and discount factors applied to result in a single figure for present value damages. In addition to property damages other damages were calculated and the following contribute to the total Present Value Benefits:  Vehicle Damages  Human Intangible Benefits  Emergency Services In Long Whatton a 100-year appraisal period has been used and future damages, costs and benefits have been discounted using HM Treasury discount rates beginning at 3.5%. For the Diseworth PLR option the appraisal period has been limited to 20 years, in-line with EA guidance. The appraisal has been carried out using a base date for estimates of July 2017, the most recent date for which inflation information (based on the Commercial Prices Index, CPI) was available at the time of appraisal. Flood damages from the MCM Handbook have been updated to the appraisal base date using CPI. An optimisation bias of 60% has been included, as specified by EA FCERM guidance for projects at an early stage of consideration.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

8.3.2 Results The NPV monetised flood damages for the entire Long Whatton and Diseworth catchment (Do Nothing) has been evaluated at £3,854k while the total NPV flood damages avoided, assuming the delivery of the proposed options, is £1,459k. These values have been broken down into the Long Whatton and Diseworth catchments separately in Figure 35.

£3,000k

£2,796k £2,500k £2,659k

£2,000k

£1,500k £1,625k

£1,000k £1,058k £937k £500k £770k BCR = 5.1 BCR = 2.1 £0k Long Whatton Diseworth -£288k -£500k

-£1,000k -£1,171k

-£1,500k

Figure 35 – Economic Damage Figures

Legend:

Do Nothing Scenario - Flood Damages Do Minimum Scenario - Flood Damages Options - Flood Damages Options - Flood Damage Reduction 8.4 FCERM Funding Based on the results in Section 8.3.2 an evaluation of the prospect for FCERM GiA funding has been undertaken using the FCERM Partnership Funding Calculator for Flood and Coastal Erosion Risk Management Grant in Aid (FCERM GiA), Version 8 – January 2014. An assessment of Diseworth has not been undertaken since PLR measures can only be claimed for OM2 Very Significant Risk properties, therefore other sources of funding would need to be secured. Since there are none in this risk bracket this option would not be eligible for FCERM GiA funding Utilising the flood damage and property risk figures derived in this project (based on the available data at the time of writing - April 2020) the amount of FCERM GiA funding that could be available (for the whole Long Whatton and Diseworth catchment) is £170k. This figure is indicative and subject to change as the project develops, accounting for the emergency of new local information, the availability of external contributions, and changes to the FCERM GiA process. This figure also assumes the FCERM GiA funding is requested covering the whole catchment as a single project. It may be more beneficial that the project is split into the Long Whatton and Diseworth catchments. This split will change the figure, likely to enable a higher FCERM GiA contribution for the Long Whatton options which are hydraulically discrete from Diseworth.

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

9 FURTHER MITIGATION & CATCHMENT RESILIENCE Over the course of this study it became apparent that reducing risk in Diseworth through a strategic capital investment in flood defence infrastructure is not affordable, under the current UK funding framework. This may change in future. At the present, it may be more practical and affordable (in the short to medium-term) to focus on exploring a suite of more cost-effective ‘non-engineering’ measures, serving to provide broad mitigation against the impacts of more frequent rainfall and to help adapt the catchment to the projected impacts of climate change. For this study and focusing on the Diseworth catchment, measures have been split into three key groups:  Monitoring & Community Preparedness – Development of hydrometric data recording and dissemination capability, provide near real-time information to inform emergency response, clarify risk and provide long-term data for further hydraulic / hydrological investigations  Adaptation & Re-purposing – Maximising the effective value of existing natural and artificial drainage structures, ensuring their function is optimal for both current and future risks  Natural Flood Management – Utilising soft natural features distributed across the upstream catchment to attenuate runoff, increasing total discharge to groundwater and reducing the severity of peak river flows 9.1 Monitoring & Community Preparedness The residents of Diseworth have reported sudden surges of flow in the watercourse, which have not been substantiated with any empirical evidence (to-date) or by the model predictions. Some reports indicated that, on occasion, the depth of flow has risen to bank level over only a few minutes. Concerns over safety could be partially addressed through the provision of early warning, if this flow is caused by controlled discharge from the EMA ponds. At the time of writing no evidence for such releases of water having occurred (scheduled or otherwise) has been obtained from any source. However, as a precautionary approach, installing effective monitoring on the EMA discharges and watercourses in Diseworth could provide critical information to enable an increased level of preparedness within Diseworth. 9.1.1 Watercourse Video Monitoring An assessment for feasible locations would need to be undertaken to establish the optimal site, in conjunction with the appropriate location on the watercourse that would more effectively capture changing flow conditions. Due to the different discharge locations from the EMA ponds it is recommended that one of the following arrangements is considered:  Single recording location at the confluence of the Diseworth Brook and Hall Gate Brook  Separate recording locations within Diseworth  Pond discharge direct recording The data could be used in future to provide reference evidence of river levels and / or flooding, as part of any re-calibration / re-validation exercise. 9.1.2 River Gauging The installation of a river gauging station on the Diseworth Brook at Diseworth would provide valuable short and long-term hydrometric data on water levels, both for community information and any future re-evaluation of the model and / or flood risk. The preferred approach would be to have this data managed within the DEFRA Data Services Platform and integrated into the EA (and 3rd

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study party sites) Flood Information Service11. This would also enable residents to sign up to the EA flood warning service, as this gauge should enable their coverage to include Diseworth. It is recommended that the gauge is installed on the Diseworth Brook between the confluence of the Hall Gate Brook and Lady Gate, shown in Figure 36. This location would ensure that flows from the whole EMA site are captured while also including the potential backwater impact of the Lady Gate road bridge downstream under flood conditions.

Recommended section of the Diseworth Brook to consider for the gauging location

Figure 36 – Recommended River Gauging Location 9.2 Adaptation & Re-purposing Strategies 9.2.1 East Midlands Airport Ponds Active Discharge Control The ponds serving EMA provide an opportunity to potentially attenuate runoff upstream of the Hall Brook and Diseworth Brook both during times of high flows and in anticipation of rainfall that could result in flooding in Diseworth. This approach would require the reclassification of the operating regime to include ‘storm water balancing’ between the summer and winter ponds, and its adoption by EMA operational managers to support the maintenance of the system. The ponds primary purpose, providing water quality management, would remain and function as the default or override mode of operation, as necessary. The more effective usage of an existing operational asset will assist EMA in achieving their sustainability and environmental commitments, specifically achieving the goals laid out in the Sustainable Development Plan12 . Reducing the reliance of the Eastern and Central transfer pumps could also generate electricity (and embedded carbon) cost savings. The delivery of such a system could be staged to enable the effective incorporation of evolving digital and data technology, and access to hydrometric data (that may be essential for the design and benchmarking of a fully operating system). A more detailed assessment of the potential technical framework for this approach has been undertaken and is presented in Appendix G for reference.

11 https://flood-warning-information.service.gov.uk/river-and-sea-levels 12 https://eastmidlandsairport.com/about-us/development-plan

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

9.2.2 Langley Priory It has been suggested by managers at Langley Priory that it may be possible to utilise the lakes (Fish Ponds) and / or the land at Langley Priory to attenuate floodwaters during extreme rainfall. The catchment upstream of Langley Priory represents 36% of the total area drained by the Diseworth Brook (at Diseworth), excluding the EMA site. Attenuating some of this runoff could provide tangible benefit in Diseworth. The lakes include a number of weir structures that function to maintain common water levels, largely for the local aesthetic and ecological value. During times of rainfall all excess flows in the Diseworth Brook will discharge over the weir structures. At present, the lakes provide minimal effective floodwater attenuation, unless rainfall heavy rainfall occurs after a prolonged dry period which has resulted in partial drying. To generate additional attenuation capacity a few approaches may be possible:  Extension to the northern lake along its eastern bank  Construction of staged weir structures, designed to increase the effective top water level under flood conditions (i.e. allowing the top water level to increase by an amount which would not cause damage to the surrounding grounds / house and was considered acceptable)  Land re-profiling works within the ground on the eastern side of the lakes to provide a functional floodplain below the weir crest level All these approaches would require some engineering / earthworks and potentially a change to the general water level under certain conditions. Alternatively, a system comparable to the EMS ponds active discharge control system (See Section 9.2.1) could allow for the lakes to be partially drained prior to forecast rainfall, enabling the effective utilisation of their current capacity without the requirement to make physical alternations. A full assessment of the potential impact on the local marine ecology would be necessary. Initially such an approach could be manually operated on site, based on an agreed operating philosophy and with forecast data provided by EMA. A more robust system would utilise actuated penstocks controlled by a ‘system’, to automate the process. 9.3 Natural Flood Management The landscape around Diseworth is relatively well suited to NFM techniques, specifically those that aim the management of runoff within agricultural land. Upstream of Diseworth it may be possible to implement staged attenuation along the main channel, in addition to distributed measures at key field and land drainage channels. LCC and currently working with Trent Rivers Trust (TRT) to formulate a bid for Local Levy funding for an NFM project in this catchment. This approach would not attract FCERM GiA funding. Constraints:  Landowner permission will be required before any features can be practically considered  The high value of arable farming this can limit the opportunity for changing the use of areas of land for NFM purposes  The high amount of sediment loading associated with arable farming can lead to issues around maintenance of in channel structures  Flood plain reconnection requires large plots of land and permissions will depend upon current and predicted land use  There are not significant areas along the watercourse that are wooded, with the potential for woody debris barriers

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

Opportunities:  There may be scope to install significant numbers of seepage barriers within ditches and modified watercourses if agreement to maintain sediments can be made with land managers  There is opportunity to plant riparian woodland strips if riparian margins can be negotiated away from intensive arable production  There may be opportunity to co-opt in field ponds to attenuate flows

Long Whatton & Diseworth Flood Risk Mitigation & Resilience Study

10 CONCLUSIONS 10.1 Flood Risk The flood modelling undertaken has demonstrated that flooding across the catchment is split into a number of distinct and relatively disconnected Wetspots (See Section 6.1). Flooding in Diseworth is general constrained to the route of the Diseworth Brook, caused by a lack of conveyance capacity and functional floodplain (caused by encroachment from development). Flooding in Long Whatton is largely the result of rapid runoff from the steep-sided surrounding landscape which exceeds the capacity of culverts and channels which route this flow through the village and into the Long Whatton Brook. The magnitude of runoff is exacerbated by unattenuated discharges from the M1. Predicted floodwater along the Long Whatton Brook does not directly impact the village, as Long Whatton is set above the natural floodplain. 10.2 Influence of the East Midlands Airport Runoff from the EMA site has been determined have a relatively minimal impact on overall flood risk in Diseworth, generally occurring during more extreme events with depths limited to less than 0.15m on average (See Section 6.2). The peak discharge rates do vary somewhat due to antecedent conditions. However, the presence of EMA ponds and drainage infrastructure (i.e. pipes) significantly attenuates the magnitude of runoff which would have occurred before the site was constructed (See Section 6.2.3). This has shown that in effect the existence of the EMA provides a significant level of protection to Diseworth. 10.3 Options Feasibility The flood mitigation strategy (See Section 7.1) was developed to ensure all practical approaches to mitigate risk were identified and suitably rationalised. The pre-evaluations and preliminary evaluations undertaken (See Section 7.3) demonstrate the difficulties in identifying suitable options for Diseworth, largely due to anticipated complexity and / or lack of real flood risk improvement, when considering the projected funding available. It was established that under current economic and funding conditions no engineering options for Diseworth would be feasible, without significant private investment. The use of PLR is considered feasible (subject to further investigations and surveys), so has been promoted as the only short-term approach to practically manage flood risk (See Section 7.4.1). The availability of land and existing drainage infrastructure help to elevate the feasibility and flood risk value of the two options developed for Long Whatton (See Section 7.4.2 and 7.4.3). The preliminary design approach for both has been to minimise major construction, focusing on more minor works to improve the routing of floodwater and highway surface water. 10.4 Economic Viability The assessment of economic viability (See Section 8.3) demonstrated that the two options in Long Whatton provide a positive return on investment, generating sufficiently a high FCERM partnership score to secure investment from the EA (subject to sign-off of an Outline Business Case). The PLR approach for Diseworth is not currently eligible for FCERM funding (See Section 8.4), requiring other sources of funding.

Data & Information Register

Owner / Project Data / Information Details Use Hyperlinks/ Risks / Issues Cost Obtained Source Need

Cut to the Long Whatton Brook river basin from 2D model build / OS MasterMap (GIS) the crossing of Derby Road (Arcadis to provide LCC Essential background mapping / flood - - Yes extent) risk mapping

CS / ICM network model(s), including any 1D network build / validation No model / foul-only model / no Sewer Network Model supporting reports and flow survey information / STW Desirable - Yes of model predictions recent verification undertaken data

IAS survey plans (which would have been Impermeable Area Survey 1D network build / 2D procured to support CS / ICM network model STW Nice to Have No data parameters builds)

Any available models and / or data covering the 1D network build / validation EA River Model EA Desirable No model - Yes Long Whatton Brook of model predictions

Cut from STW GIS database (piped / manholes / Sewer Network Data (GIS) STW Essential 1D network build Missing / incomplete data - Yes ancillaries)

Digital terrain model Missing area within catchment LiDAR (min 2m resolution) - EA Essential - Yes generation (UAV survey to supplement data)

Detailed DTM survey of site (commissioned by Digital terrain model DTM Survey LCC Essential Site coverage - Yes LCC) generation

Aerial Photography - - Nice to Have - - - No

National Receptor Database - EA Essential Economic evaluation - - Yes

2D infiltration parameters / http://www.landis.org.uk/soilscap National Soil Map - Cranfield Essential hydrogeological - - Yes es/ assessment

2D infiltration parameters / http://mapapps.bgs.ac.uk/geolog Borehole records - BGS Desirable hydrogeological - - Yes yofbritain/home.html assessment

Validation of model Surface Water Flood Mapping Standard up-to-date map product EA Desirable - - Yes predictions

Historical Flooding Records / Locations, frequency, anecdotal evidence, Validation of model Any Desirable - - Yes Reports photos etc. predictions

Highway Gully records Gully location data (ideally GIS) LCC Desirable 1D network build - Incomplete - Yes

Same data as used for the URS study. Hourly Validation of model November 2012 rainfall The University of Insufficient recording timestep / data would be OK but higher resolution (if Desirable predictions / Proving - - No records Nottingham missing data available) would be better. resilient of option proposals

Anything that could provide dimensional and / or Culvert records (as-built / condition information covering the culverts within EA Desirable 1D network build - No data available - No maintenance) the catchment.

Validation of model Sewer flood records - STW Nice to Have - - No predictions

Watercourse Structures Register

Site Information Shape Width (mm) Height (mm) Length (m) No. Pipes Inverts Survey Comments

Name Location Value Source Value Source Value Source Value Source Value Source U/S (mAOD) D/S (mAOD) Effective Weir Crest (mAOD)

Culverts

Flows can bypass the North-West of West End culvert at approximately West End M1 Circular Photo 2080 2080 15.25 Photo 46.30 Unknown 46.76 Culvert Surveyed Surveyed Surveyed 1 46.76m AOD - Unlikely to Intersection exacerbate flooding.

Effective weir crest between 57.82m AOD & 57.89m AOD - Some brick and Hall Gate North of The stone debris in channel and Circular Photo 1100 1100 68.25 Photo 56.09 55.58 57.89 Culvert Bowley Surveyed Surveyed Surveyed 2 3 x steel screen bars at mid point - Could exacerbate flooding during significant events.

Effective weir crest between 59.52m AOD & 59.84m South of Green The Green AOD - Some debris in Lane The Green Circular Photo 1400 1400 14.75 Photo 57.53 Unknown 59.84 Culvert Surveyed Surveyed Surveyed 1 channel - Could exacerbate Intersection flooding during significant events.

Bridges

Arched with central Pier(s) - Zouch Road Zouch Road Irregular Photo Irregular Irregular 9.93 Photo 32.76 Unknown 36.11 Likely to partially block Access Bridge Surveyed Surveyed Surveyed 2 during large storm events.

Single Spanning - Pipe is over 2m above river bed, unlikely to affect river flow Zouch Road during normal storm Double Pipe Zouch Road Circular Photo 800 800 11.58 Photo 33.14 Unknown 36.45 Surveyed Surveyed Surveyed 1 conditions. Could Crossing exacerbate flooding in combination with adjacent bridge.

Single Spanning - Effective North-West of weir crest between 39.07m

A6 Road Bridge A6 Zouch Road Photo 6080 4770 17.30 Photo 33.60 Unknown 39.25 AOD & 39.25m AOD - Well Rectangular Surveyed Surveyed Surveyed 1 Intersection maintained, unlikely to exacerbate flooding.

Site Information Shape Width (mm) Height (mm) Length (m) No. Pipes Inverts Survey Comments

Name Location Value Source Value Source Value Source Value Source Value Source U/S (mAOD) D/S (mAOD) Effective Weir Crest (mAOD)

Arched with central Pier(s) - Effective weir crest between 37.64m AOD & 37.94m AOD - Whilst scrub is East of Long insignificant in the primary Mill Lane Whatton Irregular Photo Irregular Irregular 4.10 Photo 34.95 Unknown 37.94 flow path, the secondary Access Bridge 1 Surveyed Surveyed Surveyed 3 Treatment Works flow path is poorly maintained. Significant storm events will be significantly impeded in this part of the cross section.

Single Spanning - Effective Adjacent to weir crest between 38.24m Mill Lane Foot Property at End Irregular Photo Irregular Irregular 1.55 Photo 36.02 Unknown 38.65 AOD & 38.65m AOD - Bridge of Mill Lane - At Surveyed Surveyed Surveyed 1 Unlikely to exacerbate Pond Outlet flooding.

Single Spanning - Effective weir crest between North-West of Mill Lane ~42.18m AOD & 42.42m Long Whatton Irregular Photo Irregular Irregular 3.65 Photo 39.92 Unknown 42.42 Access Bridge 2 Surveyed Surveyed Surveyed 1 AOD - Will only exacerbate Treatment Works flooding during significant events.

Single Spanning - Effective weir crest between 43.22m Mill Lane Road Mill Lane Irregular Photo Irregular Irregular 6.70 Photo 40.61 Unknown 43.27 AOD & 43.27m AOD - Bridge Surveyed Surveyed Surveyed 1 Unlikely to exacerbate flooding.

Arched with central Pier(s) - Effective weir crest at Mill Lane West of Mill 42.74m AOD - Secondary Access Bridge 3 Irregular Photo Irregular Irregular 4.13 Photo 40.76 Unknown 42.74 Lane Surveyed Surveyed Surveyed 2 channel and surroundings (Dilapidated) significantly overgrown – Flooding likely.

Arched - Effective weir crest Kegworth Lane between 42.82m AOD & East of Access Bridge 1 Irregular Photo Irregular Irregular 3.14 Photo 40.45 Unknown 42.96 42.96m AOD - Kegworth Lane Surveyed Surveyed Surveyed 1 (Dilapidated) Surroundings significantly overgrown – Flooding likely.

Arched - Effective weir crest between 43.30m AOD & Kegworth Lane East of 43.53m AOD - Channel has Access Bridge 2 Irregular Photo Irregular Irregular 3.30 Photo 41.30 Unknown 43.53 Kegworth Lane Surveyed Surveyed Surveyed 1 branches and a trunk (Dilapidated) blocking it - Flooding and blockage highly likely.

Site Information Shape Width (mm) Height (mm) Length (m) No. Pipes Inverts Survey Comments

Name Location Value Source Value Source Value Source Value Source Value Source U/S (mAOD) D/S (mAOD) Effective Weir Crest (mAOD)

Single Spanning - Effective weir crest between 44.45m Kegworth Lane KegworthLane Irregular Photo Irregular Irregular 10.06 Photo 41.88 Unknown 44.46 AOD & 44.46m AOD - Road Bridge Surveyed Surveyed Surveyed 1 Unlikely to exacerbate flooding.

Arched - Channel has branches and a trunk Kegworth Lane West of blocking it - Effective weir Irregular Photo Irregular Irregular 4.43 Photo 42.04 Unknown 45.51 Access Bridge 3 Kegworth Lane Surveyed Surveyed Surveyed 1 crest between 45.33m AOD & 45.68m AOD - Flooding and blockage highly likely.

Single Spanning - Effective weir crest between 44.23m Kegworth Lane West of Irregular Photo Irregular Irregular 1.19 Photo 42.41 Unknown 44.45 AOD & 44.45m AOD - Foot Bridge Kegworth Lane Surveyed Surveyed Surveyed 1 Unlikely to significantly exacerbate flooding.

Arched - Effective weir crest Sherwood Court North of Irregular Photo Irregular Irregular 4.00 Photo 43.45 Unknown 45.96 between 45.71m AOD & Access Bridge Sherwood Court Surveyed Surveyed Surveyed 1 45.96m AOD.

Single Spanning - Effective weir crest between 47.34m North of West West End AOD & 47.46m AOD - End M1 Irregular Photo Irregular Irregular 5.25 Photo 45.50 Unknown 47.46 Access Bridge Surveyed Surveyed Surveyed 1 Surface greened - Intersection Surrounding scrub significant.

Single Spanning Bridge Deck Tunnel - Effective weir North of West M1 Motorway crest 50m AOD - End M1 Photo 5470 3440 70.00 Photo 45.55 45.29 50.00 Bridge Rectangular Surveyed Surveyed Surveyed 1 Surrounding scrub Intersection moderate - Unlikely to exacerbate flooding.

Single Spanning Bridge Deck Tunnel - D/S Invert Higher than U/S - Effective weir crest between 50.17m North-East of A42 Road AOD & 50.34m AOD - The Green A42 Rectangular Photo 3730 1920 48.00 Photo 46.98 47.19 50.34 Bridge Surveyed Surveyed Surveyed 1 Surrounding scrub Intersection (Approx.) moderate - possible that metal bars could catch large debris and exacerbate flooding.

Irregular Photo Irregular Irregular 3.75 Photo 48.50 Unknown 51.26 Arched - Effective weir crest between 51.01m AOD & 67

Site Information Shape Width (mm) Height (mm) Length (m) No. Pipes Inverts Survey Comments

Name Location Value Source Value Source Value Source Value Source Value Source U/S (mAOD) D/S (mAOD) Effective Weir Crest (mAOD)

51.26m AOD - Surface greened - Some blockage North-West of The Green almost certain due to The Green A42 Access Bridge Surveyed Surveyed Surveyed 1 dilapidation of bridge Intersection structure and subsequent concrete / bricks in channel.

Arched - Effective weir crest West of The The Green between 51.70m AOD & Green A42 Irregular Photo Irregular Irregular 3.75 Photo 49.30 Unknown 52.39 Access Bridge 2 Surveyed Surveyed Surveyed 1 52.39m AOD - Some bricks Intersection and other debris in channel.

Arched - Effective weir crest between 52.00m AOD & West of The 52.32m AOD - Partial The Green Green A42 Irregular Photo Irregular Irregular 3.75 Photo 49.81 Unknown 52.32 blockage due to subsidence Access Bridge 3 Surveyed Surveyed Surveyed 1 Intersection of pier Approx. 0.48m into entrance and up to 50.70m AOD.

Single Spanning - Effective weir crest between 52.64m The Green West of The AOD & 52.75m AOD -

Access Bridge 4 Green A42 Photo 2270 1990 4.00 Photo 50.45 Unknown 52.75 Surface greened - Rectangular Surveyed Surveyed Surveyed 1 (Dilapidated) Intersection Significant tree and scrub debris U/S, Likely to exacerbate flooding.

Single Spanning - Effective North of Lady weir crest at 57.25m AOD - Lady Gate Road Gate/Brookside Trapezoidal Photo Irregular Irregular 9.75 Photo 54.01 Unknown 57.25 Urban surroundings - Bridge Surveyed Surveyed Surveyed 1 Intersection Unlikely to exacerbate flooding.

Single Spanning - Effective weir crest between 55.98m The Gables Foot End of The Irregular Photo Irregular Irregular 1.50 Photo 54.46 Unknown 56.04 AOD and 56.04m AOD - Bridge Gables Surveyed Surveyed Surveyed 1 Unlikely to exacerbate flooding.

Single Spanning - Effective Shakespeare Southern End of weir crest between 56.08m 1.00 Drive Foot Shakespeare Irregular Photo Irregular Irregular Photo Photo 54.80 Unknown 56.16 AOD and 56.16m AOD - Surveyed Surveyed (Approx.) 1 Bridge Drive Unlikely to exacerbate flooding.

The Woodcroft North of The Single Spanning - Effective Irregular Photo Irregular Irregular 1.25 Photo 55.00 Unknown 56.74 Foot Bridge Woodcroft Surveyed Surveyed Surveyed 1 weir crest between 56.65m AOD and 56.74m AOD -

Site Information Shape Width (mm) Height (mm) Length (m) No. Pipes Inverts Survey Comments

Name Location Value Source Value Source Value Source Value Source Value Source U/S (mAOD) D/S (mAOD) Effective Weir Crest (mAOD)

Unlikely to exacerbate flooding.

Single Spanning - Effective Shakespeare Western End of weir crest between 57.27m

Close Foot Shakespeare Irregular Photo Irregular Irregular 1.00 Photo 55.57 Unknown 57.52 AOD and 57.52m AOD - Surveyed Surveyed Surveyed 1 Bridge Drive Unlikely to exacerbate flooding.

Weirs

Pond upstream. Adjacent to 37.58 Approximately 2m change 38.53m Property at End Immediate D/S in water level - 38.53m Mill Lane Weir Regular Photo 9640 AOD 0.78 N/A Photo 37.01 38.53 of Mill Lane - At Surveyed Surveyed Surveyed to 36.02 Foot AOD U/S, 36.44m AOD Crest Pond Outlet Bridge D/S. 2.63m width metal silt trap immediately U/S

46.00m 46.00 North of West to Immediate D/S Trapezoidal 1770 to Trapezoidal U/S Channel A1 Weir End M1 Photo 47.25m Unknown N/A Photo 46.00 to 45.55 46.00 / V-Notch 5550 Surveyed Surveyed Surveyed dropping over the weir. Intersection AOD Motorway Crest Culvert

Channels

2400 Adjacent to 1570 Scrub During very significant Mill Lane Property at End Base, Side, storm event or blockage, Trapezoidal Photo Unknown Photo N/A Photo 39.18 Unknown N/A Channel of Mill Lane - At 1710 Surveyed 2740 Surveyed scrub side will flood due to Pond Inlet Crest Grass lower crest Side

2D Roughness Values

Roughness Value (Manning’s Land Use % of Model Area n)

Buildings 1 1%

Mature row crops 0.035 69%

Short grass 0.03 10%

High grass 0.035 2%

Rail 0.017 <1%

Roads & Paths 0.04 7%

Coniferous Forest 0.06 <1%

Scattered Coniferous Forest 0.04 1%

Mixed Forest 0 2%

Mixed Forest with Scrub 0.06 4%

Nonconiferous Forest 0.1 1%

Rough Grassland / Scrub 0.05 2%

Coniferous Forest with Scrub 0.1 <1%

Concrete 0.017 <1%

Water 0.0001 1%

Flood Risk Mapping

Infiltration Parameters

Infiltration Surface ID Horton Initial Horton Limiting

Paved - A 60.00 12.70

Paved - B 20.52 3.81

Paved - C 3.31 0.72

Paved - D 0.31 0.10

Gardens - A 87.00 18.42

Gardens - B 45.14 8.38

Gardens - C 14.74 3.20

Gardens - D 4.87 1.57

Agricultural - A 114.00 24.13

Agricultural - B 69.77 12.95

Agricultural - C 26.16 5.69

Agricultural - D 9.42 3.04

Forest - A 123.00 26.04

Forest - B 77.98 14.48

Forest - C 29.97 6.52

Forest - D 10.94 3.53

Scrub - A 105.00 22.23

Scrub - B 61.56 11.43

Scrub - C 22.36 4.86

Scrub - D 7.91 2.55

Railway - A 141.00 29.85

Railway - B 94.39 17.53

Railway - C 37.59 8.17

Railway - D 13.98 4.51

Gravel Tracks - A 78.00 16.51

Infiltration Surface ID Horton Initial Horton Limiting

Gravel Tracks - B 36.94 6.86

Gravel Tracks - C 10.93 2.38

Gravel Tracks - D 3.35 1.08

Rock or Quarry - A 69.00 14.61

Rock or Quarry - B 28.73 5.33

Rock or Quarry - C 7.12 1.55

Rock or Quarry - D 1.83 0.59

Grassland - A 105.00 22.23

Grassland - B 61.56 11.43

Grassland - C 22.36 4.86

Grassland - D 7.91 2.55

Diseworth – Property Level Resilience, Proposed Schedule

Property Level Resilience Approaches – No.

Address 100yr Property Type

Flood

Depth

(per house)

-flood -flood valves Additional external layer external Additional (perfacing) m) bricks, (render, door) (per resistant door Flood (assumes airbricks Periscope per property) 12 (assumes12 airbrick Automatic property) per resistant door Flood guards door Automatic m 2 opening) (domestic Anti (for standing barriers Free house) detached (per guard) guards Aperture (assumes per 12 covers Airbrick property) skirt Flood pump and Sump Periphery wall (based on a 40 m40 a on (based wall Periphery length) gate residential wall Periphery m)(1.2 Raisethreshold door) (per porch Storm Diseworth Heritage 1 ------Centre, Lady Gate 0.1 Church

Lady Gate, Lady Gate 0.2 Period Attached - - - - - 2 ------1 - -

Detached - - 1 - 15 1 1 ------0.1 (modern)

Detached - - - 1 - 1 1 ------13 Brookside (asm) 0.2 (modern)

Detached - - - 1 - 1 1 ------15 Brookside (asm) 0.2 (modern)

Period Detached - - - - 30 4 ------1 - 1 0.1 (asm)

Hall Gate 0.1 Period Detached - - 1 - 20 1 ------1 - 1

Attached bungalow - 0.5 ------(20th Century 14 Hall Gate 0.2 modern)

12 Hall Gate (asm) 0.2 Attached bungalow - 0.5 ------(20th Century modern)

13 Hall Gate (asm) 0.2 Attached bungalow - 0.5 ------(20th Century modern)

11 Hall Gate (asm) 0.2 Attached bungalow - 0.5 ------(20th Century modern)

Property Level Resilience Approaches – CAPEX Derivation

Address 100yr Property Type

Flood Depth

assumes 12 per 12 assumes

airbricks (assumesairbricks

-flood -flood valves Additional external layer external Additional (perfacing) m) bricks, (render, door) (per resistant door Flood Periscope per property) 12 (assumes12 airbrick Automatic property) per resistant door Flood guards door Automatic m 2 opening) (domestic Anti (for standing barriers Free house) detached (per guard) guards Aperture ( covers Airbrick property) (per house) skirt Flood pump and Sump Periphery wall (based on a 40 m40 a on (based wall Periphery length) gate residential wall Periphery m)(1.2 Raisethreshold door) (per porch Storm Diseworth Heritage £4,000 ------Centre, Lady Gate 0.1 Church

Lady Gate, Lady Gate 0.2 Period Attached - - - - - £3,375 ------£930 - -

Detached - - £1,350 - £1,125 £1,688 £2,750 ------0.1 (modern)

Detached - - - £7,300 - £1,688 £2,750 ------13 Brookside (asm) 0.2 (modern)

Detached - - - £7,300 - £1,688 £2,750 ------15 Brookside (asm) 0.2 (modern)

Period Detached - - - - £2,250 £6,750 ------£930 - £1,275 0.1 (asm)

Hall Gate 0.1 Period Detached - - £1,350 - £1,500 £1,688 ------£930 - £1,275

Attached bungalow - £1,750 ------(20th Century 14 Hall Gate 0.2 modern)

12 Hall Gate (asm) 0.2 Attached bungalow - £1,750 ------(20th Century modern)

13 Hall Gate (asm) 0.2 Attached bungalow - £1,750 ------(20th Century modern)

11 Hall Gate (asm) 0.2 Attached bungalow - £1,750 ------(20th Century modern)

Property Level Resilience Approaches – CAPEX Summary

Survey Total CAPEX Admin Total Address Property Type Cost Site Est. Costs Cost Est. Costs

Diseworth Heritage Church £4,000 £600 £4,600 £800 £5,400 Centre, Lady Gate

Lady Gate, Lady Gate Period Attached £4,305 £646 £4,951 £861 £5,812

Address Unknown Detached (modern) £6,913 £1,000 £7,913 £1,383 £9,295

13 Brookside (asm) Detached (modern) £11,738 £1,000 £12,738 £2,348 £15,085

15 Brookside (asm) Detached (modern) £11,738 £1,000 £12,738 £2,348 £15,085

Address Unknown Period Detached (asm) £11,205 £1,000 £12,205 £2,241 £14,446

Hall Gate Period Detached £6,743 £1,000 £7,743 £1,349 £9,091

14 Hall Gate Attached bungalow £1,750 £263 £2,013 £350 £2,363 (20th Century modern)

12 Hall Gate (asm) Attached bungalow £1,750 £263 £2,013 £350 £2,363 (20th Century modern)

13 Hall Gate (asm) Attached bungalow £1,750 £263 £2,013 £350 £2,363 (20th Century modern)

11 Hall Gate (asm) Attached bungalow £1,750 £263 £2,013 £350 £2,363 (20th Century modern)

Total £63,640 £7,296 £70,936 £12,728 £83,664

Total +60% bias £101,824 £11,674 £113,498 £20,365 £133,862

East Midlands Airport Ponds Active Discharge Control – Technical Overview

Option Design & Implementation Amending the operation of the ponds would require relatively limited works, the primary structural elements being:  Replacement of the Summer Pond discharge penstocks with actuated penstocks (EMA confirmed that this was being planned as a 2020 OPEX investment)  Construction / refurbishment of Summer and Winter Pond cross-connections, controlled with actuated penstocks  Construction of a new river gauging station at the confluence of the Hall Brook and Diseworth Brook To enable this operation an active control system would need to be developed to manage flows based on meteorological and hydrological data. The actuated penstocks could be controlled by either a set of systems rules or the use of a ‘Digital Twin’. Rule Based System A rule-based system would likely be possible based on a hierarchy similar to the following: 1. Water Quality - Maintain sufficient capacity within the winter ponds to ensure compliance with EA water quality permit requirements 2. Adaptation to Current Conditions - Reduce discharge rates (to the Diseworth Brook) during time of high flow, where capacity is available and winter conditions are not forecast 3. Preparation for Predicted Storm Condition - Increase discharge rates (to the Diseworth Brook) to provide available capacity, in preparation for predicted rainfall (when the rates to Diseworth Brook would be decreased) The system rules would be based on the following telemetry and real time datasets:  Rainfall forecast data (provided by the Met Office)  Air temperature forecast data (provided by the Met Office)  Ultrasonic Transducers in the Ponds (LT1 and LT2)  Recorded Diseworth Brook water levels The rainfall and air temperature data would be digested from their DataPoint Service API, which provides 3 to 5-day forecasts. It would be recommended that both short-term and medium-term forecasts are used to ensure metrological changes can be foreseen sufficiently advanced to enable the ponds to discharge as necessary.

Digital Twin System A digital twin is a digital replica of all physical assets and hydrological processes of the system within a neural network, enabling real-time predictive control. The neural network becomes better prepared for new weather as it is continually ‘re-trained’, as it experiences more weather and hydrological conditions over time. This system would be based on the ICM model, enhanced into an ICM Live model and integrated into a digital twin system developed by a proprietary software provider. ENGINESOFT are leading experts in predictive analytics and digital twin technology and would provide the capability to develop such a system. The general structure of the system, based on ENGINSOFT documentation, is shown below.

Figure 37 – Diseworth (Diseworth) – East Midlands Airport Ponds Active Discharge Control, ENGINSOFT Digital Twin System

The primary advantages of a digital twin are as follows:  An ICM Live system would be fully automated  Balance pump / penstock settings in real-time  Self-learning system, leading to medium to long-term improvements without follow-on capital investment  Based on high-fidelity hydraulic modelling  Validates system settings using only one ICM run  Minimise pump operation where possible (to generate OPEX electricity and carbon savings to EMA) The system would also include necessary overrides to provide the flexibility for operations personnel to ensure water quality permit compliance under diverse and un-predicted conditions.

The general system architecture proposed is shown in below.

Figure 38 – Diseworth (Diseworth) – East Midlands Airport Ponds Active Discharge Control, General Operational Architecture

Legend:

Existing flow route New flow route Monitoring / data feed Rule based instructions

The operation of the system would aim to compare recorded trends in the gauged water levels in Diseworth with forecast / predictive data, typically looking to identify the following:  Dropping Water Levels, occurring during dry period following the cessation of rainfall, sufficiently long enough for the natural catchment to start to drain down – the ponds discharge to be balanced against continuing dropping water levels and predicted rainfall  Low Static Water Levels, occurring after long period of dry weather (at base levels) – the ponds can be reverted to normal operating mode  Rising Water Levels, occurring during rainfall, following a period of dry weather – pond discharges can be adjusted to enable attenuation, where possible  High Static Water Levels, occurring during (or after) long period of rainfall, where the natural water levels remain high and flooding is likely – the transfer pumps will assist in balancing flow across all three locations, continuing to limit discharge where possible

The system would include overrides to maintain the current level of water quality protection, where the operational state of the system create uncertainty over the capacity of the Winter Ponds when they may be needed. Under such conditions, the system would revert to a ‘water quality’ mode and change system settings to drain the Winter Ponds as necessary. The structural viability for the use of the ponds to manage water based on the concepts outlined would need to be clarified before this option should be considered in detail.

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