3. the water cycle - west suffolk councils homepage · 3. the water cycle 3.1 introduction the...

C r ea t i ng t h e en v i ro n men t f o r bu s i n es s

Final Report © Entec UK Limited

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Page 9 November 2008

3. The Water Cycle

3.1 Introduction

The urban water cycle describes the pathways and processes through which the water we use, together with rainfall

runoff, moves through the natural and built environment, as well as through the above and below ground

infrastructure on which the domestic population and industry depend. Figure 3.1 summarises the water cycle and

how water enters, leaves and returns to the river system.

Figure 3.1 Schematic of the urban water cycle

The capacity of the water infrastructure needs to be sized appropriately to ensure the sufficient supply of clean

water to homes and industry and to receive foul drainage, whilst preventing the discharge of polluted runoff and

untreated foul drainage to protect the quality of the receiving water and any dependant habitats.

Rainfall is collected and

treated to potable

standard and pumped to

homes and other non-

domestic properties.

Waste water and foul effluent

is collected, treated and

removed from settlements.

Treated effluent is usually

discharged into the river

system.

Surface runoff from roads

and other hard surfaces

can exacerbate localised

flooding and introduce

pollutants in to streams and

rivers.

The floodplain absorbs excess

water spilling from rivers during

flood events.

Combined sewers carry storm

water and sewer water. During

heavy rainfall increased flows

can exceed capacity and

sewage is forced to overflow into

streams and rivers through

outfalls.



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3.2 Integrated Catchment Management

Development in the study area is constrained by environmental quality objectives enforced by UK and European

legislation. The Water Framework Directive (WFD) is European legislation that aims to consolidate existing

legislation. It came into force in December 2000, and was transposed into UK law in 2003. It introduces some

new environmental standards that will help to improve the ecological health of inland waters to achieve ‘good

status’. This will be achieved by:

• driving more sustainable use of water as a natural resource, through wiser consumption habits;

• creating better habitats for wildlife that lives in and around water, for example by improving the

chemical quality of water;

• progressively reducing or phasing out discharges, emissions and losses of priority substances and

priority hazardous substances;

• progressively reducing the pollution of groundwater;

• contributing to mitigating the effects of floods and droughts.

There is synergy between the philosophy behind Water Cycle Studies and WFD which is designed to ensure that

water bodies maintain or achieve ‘good status’ through the holistic management of all the contributing factors, such

as:

• pollution from specific discharge points;

• diffuse pollution related to various land use type;

• abstractions in the catchment that may be reducing the capacity of the water body to dilute pollutants;

• flooding events that may introduce additional pollutants, or modify the channel morphology, through

erosion or sediment deposition.

The influence of the Water Framework Directive on the provision and quality of wastewater treatment processes is

described in section 6.1.4.

Sustainable drainage systems that encourage infiltration and slow down the movement of rainfall runoff in the

catchment could both reduce the amount of urban pollutants entering watercourses, and mitigate the impact of

intense rainfall events on surface water flooding. Reducing the amount of potable water that is wasted by

implementing water efficiency measures, would reduce the pressure to abstract, reducing the pressure on aquatic

ecosystems, increasing the volume of water available for dilution, and conversely reducing flow in the sewer

network.



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The urban water cycle is complex and highly integrated with many feedback mechanisms. Advanced planning and

appropriate management helps to ensure that the water cycle contributes to a safe, clean and healthy environment,

rather than being a source of long term problems.

3.3 The Study Area

In order to advise on the most sustainable approach water management, an understanding of the existing natural

environment and drainage infrastructure is required. The hydrology, ground conditions and drainage of the study

area have been summarised using information from various sources, including the Environment Agency, the British

Geological Survey and the National Soils Research Institute, and consultations with Anglian Water. Figure shows

the main towns within the study area, and the WwTWs serving populations over 500. It illustrates the main rivers

into which the treatment plants discharge treated effluent. There are two SSSI sites, these are both terrestrial

woodlands and so are not directly affected by activities within the urban water cycle. There are no Special Areas of

Conservation (SAC) or Special Protection Areas (SPA) within the study area, although the Essex Estuaries is a

designated SAC, and the Blackwater Estuary and Abberton Reservoir to the south east of the district have SPA

status.

More details on specific elements of the study area are presented in this report:

• Bedrock geology and surface drift geology Figure 3.3

• Water Company zones boundaries Figure 4.1

• Groundwater protection zones Figure 6.1



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Figure 3.2 Map of the Braintree District, Haverhill and Clare study area

3.3.1 Surface Water

The District of Braintree is a broadly rural area with urban and suburban settlements. The majority of the district is

drained by three main rivers, the Blackwater and the Brain that flow to the Blackwater Estuary, and the River

Colne. The River Stour drains the north and east of the study area and may also be impacted by the projected

growth. All these rivers have an important function in the disposal of wastewater and supporting dependant

Inset: Braintree District study

area in the context of South

and Eastern England.

Main: Overview of river

networks, principal towns in

the study area, and location

of key waste water treatment

works.



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habitats, particularly the reservoirs and estuaries, in addition to the supply of water for consumption, industry and

irrigation. All the rivers flow south east into the North Sea on the Essex coastline.

3.3.2 Geology and Hydrogeology

Much of the study area is underlain by London clay, with the exception of the north around Haverhill that is

underlain by Cretaceous Chalk. The London Clay has a low permeability, meaning that water cannot move

through the rock. In contrast, the chalk is highly permeable. Overlying the London Clay and Chalk are deposits of

Boulder Clay and, within the river valleys, River Terrace Deposits. The soil has a predominantly lime-rich loamy

and clayey nature that impedes drainage.

Infiltration rates are low in the clay and rainfall is predominantly conveyed via surface runoff into the river systems

quickly. In areas where chalk is dominant, the potential for infiltration is much higher. However the overlying

drift deposits of Boulder Clay and soils impedes infiltration.

The London Clay is classified as a minor aquifer. The formation has low permeability and little groundwater yield

for mains public water supply, but may be an important source for local supplies and to maintain baseflows in to

the rivers. The London Clay overlies Cretaceous Chalk at a depth of around 30 to 60m between Braintree and

Witham. The Chalk is classified as a major aquifer with high permeability and provides groundwater abstractions

for public water supply and other uses.

Figure 3.3 shows the bedrock geology and the surface drift geology of the Braintree District, Haverhill and Clare

study area.

The following technical sections describe the different elements of the water cycle and assess the current capacity

to accommodate proposed growth across the study area. Capacity issues that pose a potential barrier to

development are highlighted together with a review of the strategic options proposed by the water companies and

recommendations for Local Authorities and Developers to consider.



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3.4 Climate Change

It is important to take into account the predicted impacts of climate change when considering surface water

management, as advocated within PPS25 and PPS1. The changes in global climate patterns are predicted to lead to

increased global temperatures, cause sea levels to rise and increase the frequency and intensity of rainfall and

extreme weather. At a regional scale the nature of impacts will vary, and will depend on the levels of greenhouse

gas in the atmosphere. Alternative forecasts have been calculated based on varying greenhouse gas emissions

scenarios by the U.K. Climate Change Impacts Programme (UKCIP). For Essex, under a Medium-High emissions

scenario in the 2050s, the 2002 UKCIP predictions1 forecast an increase in rainfall of between 15% and 20% in the

winter accompanied by decreases in summer rainfall of between 20% and 30%.

Entec has reviewed the published Water Resources Management Plans (WRMPs) to confirm that both Anglian

Water and Essex and Suffolk Water have incorporated the most likely impacts of climate change into their resource

and demand forecasts. Both companies have also used good practice to take account of the uncertainties associated

with climate change. The water supply component of this Water Cycle Study is based on the data provided by the

water companies, and so the impact of climate change.

PPS25 uses data extracted from UKCIP2 to detail the allowances that should be made to accommodate climate

change. Allowances will be needed to manage increased rainfall and the subsequent increase in runoff that will be

generated. PPS25 expects new developments to be designed to accommodate the impacts of increase runoff from

climate change. Sustainable Drainage Systems (SuDS) will become more important to manage increased rainfall

during the future winters and during extreme storm events. Drainage recommendations are inherently site specific

and so the impacts that climate change may have on the need for, and design of, sustainable drainage should be

considered further in the more detailed Phase 2 WCS.

1 Climate Change Scenarios for the United Kingdom, The UKCIP Scientific Report, UKCIP, April 2002

2 www.ukcip.co.uk

Chelmsford

Braintree

Witham

Haverhill

Sudbury

Halstead

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Reproduced from the Ordnance Survey mapping with the permission of the Controller of Her Majesty's Stationery Office. © Crown Copyright.

Unauthorised reproduction infringes Crown Copyright and may lead to prosecutions or civil proceedings. Braintree District Council O/S Licence No LA 100018490. 2008

22058b006 fiell

Braintree District Council

Water Cycle Study

Figure 3.3

Geology and Hydrology of Study Area

Approx Scale: 1:211,000 @ A3

November 2008

0 1 2 3 4

Kilometers

N

H:\Projects\HM-255\22058 Braintree Water Cycle Strategy\D040 Design\ArcGIS

Key:

Study Area

Drift Geology

Peat & Peaty Soils

Alluvium & Lacustrine Deposits

Beach & Tidal Flat Deposits

River Terrace Deposits

Head - undiff

Clay & Silt - undiff

Lowestoft Formation - Silty Clay

Glacial Till

Glaciofluvial Deposits

Solid Geology

Crag (sandstone)

London Clay

Lower London Tertiaries

Upper Chalk

River

Development sites > 1ha

Main Urban Areas

Rive

r Coln

e

River B

lackwater

Rive

r Brain

River Stour

Chelmsford

Braintree

Witham

Haverhill

Sudbury

Halstead

570000

570000

580000

580000

590000

590000

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Rive

r Coln

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River B

lackwater

Rive

r Brain

River Stour

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