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Principles of water

The water cycle is fundamental to the geography, ecology and quality of life in Hertfordshire. Hertfordshire is located within the driest region in the UK.  Its physical characteristics, such as the mix between growing urban settlements and productive rural landscapes, and different soil types, place it at risk from diminishing water resources.  Economic development and increased housing numbers mean Hertfordshire’s built environment can affect the natural water cycle in multiple ways:

      • The rate of abstraction of groundwater.
      • The fate of rainfall.
      • The volume and quality of water run-off.
      • The quality of water coursesThe rate of recharge of the aquifer.

Maintaining a balance between each of the above is crucial for protecting sensitive habitats (such as chalk streams), for minimising the risk of flood damage and for ensuring a sustainable source of fresh water for human consumption.  However, development has traditionally paid little attention to water efficiency or management.  

According to the Hertfordshire Quality of Life report 2014, the water consumption rate is 170 litres per person per day for unmetered customers. Since 2004/05, there has been a trend falling of water consumption in this year, water consumption reached the peak level of 188 litres per person per day.   

Climate change projections forecast that by 2050, Hertfordshire could see a 17% increase in rainfall or snow in winter, and a 19% decrease in rainfall during the summer.  The potential increase of drought conditions in summer is well documented.  The increase in flooding episodes, in summer as well as in winter, is less obvious and must also be brought into planning consideration.

To avoid significant problems in the future, major improvements are required in the way the built environment is planned and designed.  Developments must act in synchronisation with the natural water cycle to avoid an imbalance between water extracted and that returned to the groundwater and aquifers. These improvements fall under the collective heading of ‘Integrated Water Management’.  This module reviews the importance of planning for Integrated Water Management and some typical solutions it entails.

View the latest Hertfordshire Quality of Life Report.

The Water Cycle 

water - basic principles - water cycle

Impacts of the built environment on the water cycle

The built environment, and new development in particular, can have a significant impact upon water cycle process both at the immediate site level and the larger, regional scale. 

These impacts can be grouped into four interrelated areas.

Flood risk

Development of land has traditionally resulted in surfaces that are impermeable to rainwater, such as industrial and commercial estates, housing estates, roads and other urban areas.  Each of these can increase the risk of surface water flooding (‘pluvial’ flooding), which, along with ground water flooding, is the greatest source of flood risk for Hertfordshire, more so than river flooding (‘fluvial’ flooding).  The majority of pluvial flooding is caused by run-off from areas of impermeable surface. 

Flood risk management guidance can be found in the National Planning Policy Framework 2012 and Flood Risk and Coastal Change Guidance 2014. Inappropriate development in areas at risk of flooding should be avoided by directing development away from areas at highest risk, but where development is neccessary, making it safe without increasing flood risk elsewhere.

Local plans should be supported by Strategic Flood Risk Assessment and develop policies to manage flood risk from all sources, taking account of advice from bodies such as lead local flood policies and internal drainage boards. Local plans should apply a sequential risk-based approach to the location of development to avoid where possible flood risk to people and property and manage any residual risk, taking account of the impacts of climate change by:

  • Applying the sequential test.
  • If neccessary, applying the exception test.
  • Safeguarding land from development that is required for current and future flood management.
  • Using opportunities offered by new development to reduce the causes and impacts of flooding.
  • Where climate change is expected to increase flood risk so that some existing development may not be sustainable  in the long-term, seeking opportunities to facilitate the relocation of development, including housing to more sustainable locations.

Environment Agency flood maps indicate that there are areas at risk of fluvial flooding in Hertfordshire. Indicative flood plain represents land which lies beneath either the tidal 1:200 year or fluvial 1:100 year return period water level.

The River Lee and its tributaries which rise in Hertfordshire and flow south to the Thames, have a significant flood plain area, especially to the south - Bishop's Stortford, Ware and Hertford all lie on or immediately adjacent to the floodplain. There are a number of settlements along the flood plain on the Broxbourne-Epping Forest border, including Broxbourne and Cheshunt. There are also floodplains along the other rivers in the county, for example the Colne has historically been prone to flooding.

Water abstraction and treatment

The Environment Agency issue and manage licences for the abstraction and treatment of groundwater for domestic, commercial and industrial uses.  Hertfordshire lies within three Environment Agency Regions: Thames, North East and Anglian (in Central Anglian and West Thames).  

Many of the sources within these regions are already close to or at their maximum abstraction level. For instance, the Anglian region is the driest region in England and Wales and there are large areas where no further water is available during summer and some areas where damage is already occurring. Parts of the River Lee catchment are also suffering from unsustainable abstraction. The Thames region also suffers from demand pressures.

Domestic consumption of water is higher in Hertfordshire than anywhere else in the country.  Groundwater provides a third of our drinking water.  

If sufficient water is to be available to support the current and predicted future demands of Hertfordshire’s population, there will have to be significant changes to the rate at which groundwater is abstracted and recharged, so that they are balanced and sustainable in the long term.
Increasing the rate of recharge of the groundwater source will be a critical factor for reaching a sustainable level of abstraction. Surface water drainage maintains the flows into the local water bodies (rivers, streams and lakes) and recharges the ground water. Therefore, by improving surface water drainage to natural watercourses, we are able to maintain a higher groundwater abstraction rate. Failure to improve surface water drainage will mean abstraction rates will have to fall further. 

To protect groundwater the Environment Agency has defined Groundwater Protection Zones, where the Environment Agency seeks to restrict certain types of development. Groundwater protection zones cover all the land draining the groundwater resource.  For instance, a groundwater protection zone serves to protect the major aquifer which covers North and East Hertfordshire and also extends east into Essex.

Climate change

The emissions arising from constructing, heating, cooling and servicing buildings are recognised as significant factors that contribute to global climate change. Climate change in turn presents a number of risks to buildings and the built environment in general, with many revolving around the water environment and cycle. The effects of climate change therefore provide further incentive for Integrated Water Management.

Climate change projections for Hertfordshire forecast an increase in average temperatures and an increase in the number of extreme weather events. Hertfordshire County Council commissioned a Climate Change Risk Assessment using the latest UK Climate Projections (UKCP09). The headline messages from the Risk Assessment are provided in the Climate Change Adaptation module, but key findings included: 

  • General precipitation - More variable patterns of rainfall and snow, which is anticipated to result in drier summers, increased rainfall during the winter, and more frequent severe weather.
  • Extreme rainfall - More intense rainfall falling in winter months.  Towards the end of the century rainfall on the wettest day in winter could increase from 2009/10 levels by up to 56%.

Both of these may result in increased flooding episodes, particularly in urban areas. Less rainfall is expected during the summer months; however, a prolonged period of dry, hot weather causes the ground to dry, which reduces its ability to allow water to infiltrate quickly enough when a short but heavy rainfall event does occur. 

The resulting excess water run-off can lead to flash flooding, particularly where there are also impermeable man-made surfaces.  For instance, the hot summer of 2006 triggered thunderstorms and torrential rain which caused localised flooding across England.  The town of Royston, North Hertfordshire suffered from flash flooding that blocked roads and caused damage to properties. 

Water quality

The abstraction and discharge of water used in the built environment can have a detrimental impact on the quality of the local waters, which in turn can impact biodiversity and the ecological habitats of wildlife. The Hertfordshire Environmental Forum (HEF) published in 2006 an update to the “50-year vision for the wildlife and natural habitats of Hertfordshire”. This Local Biodiversity Action Plan identifies many important ecological habitats particularly sensitive to water quality. The list provided in the Wetlands Habitat Action Plan section includes:

  • Wetlands - within Hertfordshire this includes rivers, streams, springs, water-cress beds, ponds, lakes, reservoirs, sewage works, marshes, fens, swamps, wet grassland and carr woodland;
  • Chalk rivers - all chalk rivers are fed from groundwater aquifers, producing clear waters and a generally stable flow and temperature regime. The majority of European chalk rivers are found in southern England;
  • Open water - can be remarkably rich in plant and animal life; however, many are prevented from reaching their full potential due to factors such as pollution, lack of water and poor management;
  • Wet grasslands - to be found where groundwater levels are close to, but not permanently at, the surface and where the grassland is affected by seasonal flooding; and
  • Urban habitats - such as urban wetlands, encapsulated countryside, managed green space, naturally regenerating habitats and ‘urban commons’.

The most recent  Quality of Life report has shown that 9.8% of Hertfordshire's water bodies are classified as good and 39% are classified as moderate. This may appear as a significant decrease in water quality however, since 2009, the Environment Agency have been targeting water bodies where there is not enough evidence to improve the knowledge and certainly of the true ecological status of the water bodies. The Environment Agency does not think that this shows a true deterioration in the environment.

Achieving this improvement has required significant efforts. To improve yet further, the following need to be monitored and controlled: 

  • Abstraction of water from the water environment.
  • Point source discharges and diffuse sources liable to cause pollution.
  • Catchment of surface water.
  • Potential impacts to surface water habitats.
  • Artificial recharge or augmentation of ground water.

The protection and restoration of water quality is required by the Water Framework Directive, which has the overall objectives to prevent deterioration of the water environment and to restore waters to good status by 2015.

(WFD) (Directive 2000/60/EC) provides common objectives, guidelines, strategies and requirements for the member states of Europe to prevent deterioration and to provide improvement of water quality. The Water Environment Regulations 2003 (England and Wales) provide the framework to meet the WFD objectives of protecting and enhancing the country’s water bodies and groundwater by 2015.

Principles of integrated water management

To avoid significant problems in the future, major improvements are required in the way the built environment is planned and designed. Developments must act in synchronisation with the natural water cycle to avoid an imbalance between water extracted and that returned to the groundwater and aquifers. The improvements required fall under the collective heading of Integrated Water Management (IWM). 

IWM aims to ensure that the manmade built environment is planned and designed to function in partnership with the natural water environment, so that they can both be of high quality and sustainable.  IWM has a number of sub-management processes, which can each be related to the natural water cycle.

Minimise the consumption of water

Hertfordshire has one of the highest domestic levels of demand for potable water. As additional built development takes place, the abstraction, treatment, distribution and consumption will become increasingly challenging. A significant amount of energy and chemicals is consumed in treating water to drinking water standards and transporting it to consumers. It is therefore vital that the demand on primary water resources is reduced or managed as far as practicable.
In 2008 DEFRA published the Government’s water strategy for England, “Future Water”. It contains some relevant facts: 

  • Household water demand has been increasing since the 1950s, due to population growth and changes in the way we use water in the home, and is now more than half of all public water supply use.
  • Almost one third of the water we use is, after being treated to what is among the best drinking water quality standards in the world, at significant financial and environmental cost, simply used to flush our toilets.
  • Average water use in England is about 150 litres per person per day (l/p/d).

Building Regulations Approved Document Part G addresses sanitation, hot water safety and water efficiency. The 2010 revision requires the total water consumption of a new home to not exceed 125 litres per person per day. Achieving this requires the installation of more efficient fittings and solutions such as:

  • Efficient toilets, taps, showers and household appliances.
  • Leakage detection and prevention.
  • Minimal use of potable water for landscape irrigation.
  • Rainwater, greywater and surface water runoff collection and reuse systems.

The Environment Agency is a useful source of information on water efficiency solutions. They published their research entitled ‘Conserving Water Use in Buildings’.

Use and reuse alternative water sources

Most water is used for non-potable purposes and therefore does not actually require wholesome mains water. Alternative sources can be used, for example, for washing clothes and vehicles, flushing toilets and watering plants. Once used, water can often be filtered, treated and reused. Harvesting and storing alternative water sources (e.g. in cisterns, underground tanks, or ponds) can significantly reduce or eliminate the volume of mains water consumed. This presents environmental and financial benefits, including:

  • Reduced pressure on the water supply infrastructure.
  • Less flowing into surface water drainage systems.
  • Lower water bills to the owner.

Five alternative sources are considered further in the solutions section:

  1. Rainwater
  2. Greywater
  3. Blackwater
  4. Open water
  5. Lower grade water

Once further reuse of water is not practicable, the discharge should if possible be to a sustainable soakaway or watercourse, which will subsequently assist in recharging the groundwater and aquifer. An exception must be made if the chemical content of the wastewater dictates a discharge to sewer.

Minimise the wastage in water distribution

Future Water contains more relevant facts regarding the wastage in water distribution systems:

  • Almost one quarter of all water supplied is lost through distribution leakage.
  • Completely eliminating leakage would be impossible, particularly as in many cases we are left with Victorian infrastructure.
  • Since total leakage peaked in 1994/95, it has been reduced by 33% in England and Wales.
  • Of the water lost through leakage, about one quarter is lost through customers’ supply pipes.

The final point is important as it emphasis the benefit of detecting and preventing leakages within the demise of development. Smart water meters are capable of highlighting any abnormal patterns of water consumption, which often leads to the identification of a leak. Non-domestic developments targeting a BREEAM rating can gain a credit for water leak detection systems, when they extend the full distance between the building and the point of mains connection.

Manage surface water drainage and storm overflow

To recall, Building Regulations Approved Document Part H (2002), requirement H3, prioritises the options for runoff as: 

  • An adequate soakaway or some other adequate infiltration system.
  • A watercourse.
  • A sewer.

The hierarchy is matched by the National Planning Policy Framework Paragraph 103 of the NPPF states: “development is appropriately flood resilient and resistant, including safe access and escape routes where required, and that any residual risk can be safely managed, including by emergency planning; and it gives priority to the use of sustainable drainage systems. ”

As well as managing the surface water run-off, the NPPF aims to prevent increasing the risk of flooding. Paragraph 100 which states: “ Inappropriate development in areas at risk of flooding should be avoided by directing development away from areas at highest risk, but where development is necessary, making it safe without increasing flood risk elsewhere.” The various components of a sustainable drainage system (SUDS) are reviewed in the solutions section.

Where practicable, SUDS should be designed to ensure the sustainable drainage networks have the additional capacity required to cope with infrequent weather conditions and therefore to reduce the flood risk to the development. Using SUDS to manage surface runoff and storm overflow has multiple benefits: 

  • Increased recharge of groundwater and aquifers.
  • Reduced runoff into sewer system (resulting in reduced energy and chemical costs of treatment).
  • Improved groundwater quality via natural infiltration.
  • Reduced degradation of chalk stream habitats.

It is essential that the ownership and responsibility for maintenance of every sustainable drainage element is clear; the scope for dispute kept to a minimum; and durable, long-term accountable arrangements made, such as the allocation of management companies.

Improve water quality

In the words of Hertfordshire Environmental Forum’s “50-year vision for the wildlife and natural habitats of Hertfordshire”:

“Water quality deteriorates with increasing urbanisation as surface run-off carries with it increasing loads of pollutants and sediments. Rain falling onto towns has the beneficial effect of washing away much of the accumulated dirt from the previous dry period. However, the result is that stormwater may contain a wide variety of pollutants including suspended solids, nutrients (nitrogen and phosphorus), toxins (including heavy metals and pesticides), pathogenic microorganisms (bacteria, viruses and others), oil, detergents and de-icing chemicals. The problem of pollution by sewage and industrial wastes is not confined to urban areas. However they more often have their origins in urban areas and so the effects are most concentrated there.”

Effective development drainage strategies as part of an Integrated Water Management strategy to mitigate overflow following heavy rainfall will help to prevent unmanaged surface water contamination.

Benefits of integrated water management

Choosing the right solutions delivers lots of benefits:

  • Water efficient appliances in homes, to reduce the water bills of consumers and the abstraction of fresh water.
  • Alternative water sources, to allow the groundwater and aquifers to recharge.
  • Using non-potable water for activities that do not require it (e.g. toilet flushing), to reduce the consumption of energy and chemicals in treating and transporting water.
  • Applying onsite management of water runoff, to reduce water utility infrastructure (e.g. stormwater drainage).
  • Laying out a development to promote natural drainage, to reduce the risk of surface water flooding.
  • Enabling the groundwater and aquifers to recharge, to reduce the pressure to control lifestyles and water use (e.g. summertime hosepipe bans).
  • Use vegetation to improve the quality of runoff water, to benefit natural habitats and biodiversity.

Hertfordshire typical household water use

Water - basic principles - typical household water use

 

Hertfordshire good practice household water use

Water - basic principles - good practice household water use

 

 

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