Keywords
Groundwater
Future cities
Visions
Urban
Scenarios
1. Introduction
As
urban populations continue to dominate globally, city planners, urban
innovators and researchers are increasingly working on joint initiatives
to investigate the physical, technological, social and political
aspects of harmonized urban living. The aim is to create cities which
perform well, that are, prosperous, sustainable, resilient, and
liveable. Whilst significant attention is given to smart city
information technologies, data and innovation products, the broader city
initiatives tend towards ‘future city’ concepts where knowledge
dissemination, cooperation, policy reform and urban design run in
parallel with big data and smart technologies (Rogers et al., 2012; Angelidou, 2015). Despite this broader approach to future city thinking John et al. (2015),
in their review of 92 urban visions across 13 countries, found that
sustainability principles were poorly covered and that no city fully
integrated all of the defined sustainability principles (i.e. relating
to built form; ecosystems services; resource consumption and production;
social and cultural practice; governance, and; city-catchment systems)
within their vision. In the context of a sustainable urban future, the
vision may be defined as a desirable society, which provides permanent
prosperity within biophysical constraints and in a manner that is fair
and equitable now and in the future (Costanza, 2000).
A city foresight exercise, undertaken by the UK Government Office for
Science, aims to gather science evidence in support of policy decisions
to inform the analysis, design and transformative actions needed to
shape the UK’s urban future (GO-Science, 2016).
Adopting a trans-disciplinary approach, the foresight exercise
considers urban economies, metabolism, form, infrastructure, governance,
and city living. At a time when sustainability principles need
promoting in city visions, inclusion of urban metabolism is critical.
Originally proposed by Wolman (1965)
urban metabolism may be defined as the inflow and outflow transactions
required to sustain city functions, or the production, consumption and
disposal of resources (Huang and Hsu, 2003).
In this way the biophysical demand to sustain urban society is
evaluated. Linking urban metabolism concepts with future city programmes
brings another dimension to urban performance metrics by making the
connection between the city and its resource support area, commonly
referred to as its hinterland (Lee et al., 2016).
Here, there is an acknowledgment that, in terms of resource demand, the
city cannot sustain itself using only materials within the city limits
and additional resources must be imported; and it follows that the
by-products, or waste, arising from city metabolism are also disposed of
beyond the city boundary. Strongly aligned with urban metabolism
principles is the ecosystem services approach adopted by UK National Ecosystem Assessment (2014)
through the Natural Capital Asset Check. Here the ecosystem services
(stocks and flows) provided by the natural environment within the city
and its hinterland are evaluated. However in their review of
sustainability in city visions, John et al. (2015)
conclude that the visions which are led by city representatives
emphasize the functioning of the built environment within the city
limits only, and the relationship with the hinterland is weak.
Furthermore, they argue that this leads to a reduction in city
resilience as experts on the hinterland are not represented and
therefore not involved in the design of solutions.
Water supply and disposal form two critical components of the city’s metabolism that become more acute as cities grow (Wolman,1965; Jones, 1966), particularly as ecosystem service demand and consumption of resource per capita are outpacing population growth (John et al., 2015).
In recent decades the rate of demand for water has been twice the rate
of population growth and, under a business-as-usual climate scenario, a
40% global water deficit is predicted by 2030 (UN-WWAP, 2015).
As traditional water sources become depleted there is an expectation
that cities will need to exploit their hinterlands to broaden their
water supply catchment area, utilize marginal water resources and invest
in innovation solutions and more advanced technologies to manipulate
the natural water systems. The internal city processes that facilitate
the supply, consumption and disposal of resources disturb natural
systems and alter the urban environment and morphology (Huang and Hsu, 2003).
Disturbance of the natural water environment in urban areas and
pressure on the ecosystem services it provides is likely to become more
pronounced where the physical expansion of cities is occurring at a
faster rate than population growth (Sterling et al., 2012; Hunt et al., 2016). As a result inclusion of water within urban metabolism and future cities assessment is common (Rojas-Torres et al., 2014),
but explicit consideration of urban groundwater systems is not, which
is symptomatic of the fact that ecosystem services provided by urban
underground space are not yet appreciated by most city representatives (Hunt et al., 2016).
It
is estimated that half of the world’s megacities are
groundwater-dependent and over 40% of water supply across much of Europe
comes from aquifers lying beneath urbanized areas (Wolf et al., 2006).
Additionally, groundwater resources in urban areas do not just extend
to water for domestic and industrial supply but also to ground source
heating. For example, in London it is estimated that 19% of the city’s
total heat demand (2010) could be derived from ground heat sources (GLA, 2013).
The interaction of groundwater with other urban systems, such as
infrastructure and surface water networks is well-recognized by expert
practitioners and is increasingly on the city agenda, for example in
consideration of baseflow provision to urban and peri-urban rivers (blue
networks), flood risk, management
of blue-green infrastructure (e.g. sustainable drainage systems),
adverse effects on underground infrastructure, control of underground
construction, and impacts of industrial legacy on water quality. These
different examples highlight the range of urban groundwater processes
that operate at different temporal and spatial scales and across the
rural-urban transition.
Here we consider the factors that affect the groundwater cycle in urban
environments where the interaction between the anthropogenic and
natural environment causes not only physical alteration to the ground
but also a change in natural capital stocks, disturbance to natural
flows and shifts in natural boundary conditions.
Using
London, the UK’s megacity as a case study, the complexity of
groundwater systems in urban and peri-urban environments is illustrated.
A semi-quantitative water balance method is used to highlight a number
of physical, social and political interactions between the natural
environment and anthropogenic activity and to account for changes to the
groundwater system that may arise as a result of future city
interventions. Insights into urban water management to underpin
plausible and scientifically-informed city visions and interventions are
provided.
2. Urban-groundwater systems
Conceptually,
urban groundwater accounting should follow the path of the water cycle,
which essentially comprises a system of recharge or replenishment by
rainwater through the unsaturated zone;
storage and through-flow within underground voids (fractures and pores
in the subsurface geology), and; discharge or abstraction via springs,
rivers or boreholes. Using this approach, consideration can be given to
the constituent elements of urban development that intervene in the
natural water cycle, thereby impacting the quality and quantity of the
resource (Table 1).
Rates of water movement are also fundamental to water accounting in
terms of both water quantity and water quality. Therefore one also needs
to establish: [1] resource catchment boundary conditions in terms of
recharge and base-level (the level to which groundwater flows, e.g. the
main river of outlet at the sea) and [2] physical material properties
such as porosity and permeability (the underground voids and their
degree of connectivity).
Table 1. Anthropogenic interventions in the urban water cycle (recharge, through flow and discharge).
| Human intervention | Potential impact | |
|---|---|---|
| Recharge | ||
| Evaporation | Climatic warming allows more moisture to be held in the atmosphere. | Increased rainfall and increased intensity of individual rainfall events. |
| Hard surfacing (anthropogenic aquitards) and reduced vegetative cover. | Potential reduction and redistribution of effective porosity. Reductions in the potential for evapo-transpiration. | |
| Funnelling of wind through high storey developments. | Increased evaporation. | |
| Run-off | Hard surfacing (anthropogenic aquitards). | Increased run-off and reduced baseflow to surface water courses; potential to mobilize more sediment; water arrives more quickly increasing the potential for contaminant mobilisation. The reduced run-off times and base flow result in greater flashiness of surface water courses. Layers of hard surfacing, e.g. palimpsests of development may result in multiple levels of perched water. |
| Recharge | Hard surfacing | Reduction in natural groundwater recharge: exacerbated by silt and sediment clogging; local increases in recharge associated with pipe leakage, and anthropogenic aquifers (e.g. gravel packs to services). |
| Made Ground | Increase in near surface storage, particularly in areas underlain by low permeability lithologies. | |
| Quarrying | Local increases in the extent of bare ground available for recharge. | |
| Urban development | Leakage from pipes; irrigation water (parks and recreation areas); potential for groundwater level rise beneath urban environments. Granular bedding materials form anthropogenic aquifers. | |
| Freshwater/saline interface | Dewatering | In coastal environments dewatering and lowering of the groundwater table may lead to saline intrusion. |
| Through-flow and storage | ||
| Water as a resource. | Lowering of groundwater table and changes to geochemistry, increased depth of unsaturated zone. Increased hydraulic gradients, potential to mobilize contaminants to greater depth. Potable supply can result in cross-catchment transfer of water. The introduction of artificial storage (e.g. reservoir storage to maintain water supply) removes groundwater from aquifers. Overuse may result in derogation of supply. | |
| Dewatering | In coastal environments dewatering and lowering of the groundwater table may lead to saline intrusion. | |
| Culverting of watercourses in unconfined aquifers. | Water culverted to allow access across watercourses; may affect recharge processes; potential impact on quality (reduced oxygenation). | |
| Geothermal energy. | Changes to ground temperature with potential impacts on evapo-transpiration | |
| Deep construction, e.g. underground tunnels, reservoir construction, landfill. | Compartmentalisation of water; a more irregular water table, and time of vadose zone recharge lengthened by obstacles to flow. | |
| Discharges, e.g. soakaways. | Ponding of water may alter flow paths. | |
| Moving water through the unsaturated zone more quickly as a result of underground development and physical disturbance to the ground. | May result in a change to groundwater chemistry, e.g. negative saturation indices move to greater depth in the aquifer, resulting in changes to baseline water chemistry; dry fallout moved deeper into the aquifer. | |
| Discharge | ||
| Industrial discharge to surface watercourses, e.g. process and mine water, contaminated drainage from industrial units. | Changes to water quality and temperature impacts on ecology. | |
| Use of abstraction wells. | Alters flow to natural discharge points. | |
The
key components of urbanisation that impact on boundary conditions
(points of recharge, discharge or barriers to flow) are: alteration of groundwater tables
as a consequence of resource exploitation, dewatering for construction,
quarrying and industry and leakage from urban water transport systems
or tunnel drainage. Where these effects are measurable at a regional
scale they are monitored through groundwater level monitoring, e.g. by
environmental regulators and by resource suppliers such as Thames Water Utilities
Ltd (TWUL) in London. Mathematical modelling in conjunction with
geospatial analysis can be used to evaluate these impacts and their
sensitivity, e.g. the conceptual model presented for Bucharest, Romania,
by Boukhemacha et al. (2015) or Jones et al. (2012).
The physical properties of urban groundwater systems are altered by a range of anthropogenic interventions (Table 1).
The greatest impact results from the construction of near surface and
buried low permeability layers that impede water flow. Anthropogenic
construction of hard surfacing in urban environments takes a range of
forms from foundations, tunnels and reservoirs to the provision of
buildings with their associated services, such as parking, storage and
leisure facilities, e.g. sports areas, including swimming pools and the
range of buried services that convey people and resources (water, energy
and waste) beneath ground. The construction of “impermeable hard
surfacing” not only limits water infiltration
to the ground by virtue of the low permeability of the construction
materials, but it is also commonly associated with ground loading and
compression, which closes near surface voids, further limiting
infiltration. The presence of surface hard standing both increases
overland flow (rather than infiltrating the ground to replenish
aquifers) and focuses accelerated surface flow to surface drainage
systems. The consequential surface water flooding is increasingly
occupying the minds of planners (e.g. Pitt Review, 2008; Slingo et al., 2014) and modellers since the early 1990s (e.g. Macdonald et al., 2012; Jankowfsky et al., 2014), leading to the realization that urban systems have to be viewed in an integrated manner and in terms of the host river catchment (i.e. the entirety of their recharge area), e.g. River Basin Catchment Management plans (Jaspers, 2003).
Though
not explicitly considered here in the groundwater accounting exercise,
changes to groundwater quality in the urban environment may result from a
number of impacts, including: contaminating land uses, leaking
infrastructure industrial cooling and processing water, leachate from
landfills and other industrial discharges. Many of these impacts occur
at discrete points (point-source pollution) or occur along linear routes
such as transport networks or drainage channels. Furthermore, many
major urban developments are close to the downstream end of catchments,
because their development is closely associated with water transport and
trading and where natural groundwater is supplemented by anthropogenic
sources that are situated farther upstream, e.g. mine drainage impacts
on the River Humber (Neal and Robson, 2000).
This reinforces the fact that urban groundwater systems cannot be
considered in isolation, but as part of connected catchment or
hinterland. As well as exposure to a large range of contaminants, there
are changes in groundwater quality that are brought about as a
consequence of physical changes to the groundwater environment, e.g.
saline intrusion in coastal cities where influx of sea-water occurs as a
result of groundwater lowering–often as a result of groundwater
abstraction, or changes in Oxidation/Reduction Potential (Eh) or pH
conditions that result from a change in groundwater level, including for
example culverting of surface water. There is an extensive literature
that describes these impacts, e.g. (Barker et al., 1998; Everard and Moggridge, 2012). However, to date cost accounting has not been fully embraced in this conceptual understanding, e.g. Banks et al. (2014). Some of the impacts are well understood, e.g. the macropollutants determined from monitoring the impacts of landfill (Peel, 2014) septic tanks and sewage networks (Navarro and Carbonell, 2007) and legacy industries (Hatheway and Doyle, 2006). This contrasts with low levels of understanding with respect to the impacts of emerging groundwater contaminants (Stuart et al., 2012), such as micropollutants (Musolff et al., 2009) and nanoparticles (Baun et al., 2009).
Specific determinands commonly detected in UK groundwater include
pesticides, metabolites, pharmaceuticals including carbamazepine and triclosan, nicotine, food additives and alkyl phosphates (Stuart et al., 2012).
There are a number of other impacts which to date have been less well constrained, but nevertheless are identified in Table 1. Many of these impacts broadly align with the direction of climate change (Taylor et al., 2013), consequently mitigation of urban impacts aligns well with developing broader climate change resilience.
As well as exacerbating the potential for surface run-off to contribute to the issue of surface flooding (Perry and Nawaz, 2008), the construction of paved areas leads to the reduction of moisture in the soil zone and reduces the potential for evapotranspiration
in these areas, in turn leading to changes in the engineering
properties of near-surface soils. A level of mitigation can be achieved
through green roofs, which provide additional benefits of lowering
absorption and release of solar radiation. The penetration of
foundations into the unsaturated zone has the potential to block
groundwater flow paths, resulting in localized focusing of flow, and
provides the potential for compartmentalisation of groundwater, which
can potentially impact on water quality and resource availability. There
is potential to mitigate against these impacts through the use of
sustainable drainage systems (SuDs), which comprise alternatives to
channelling surface water through networks of pipes and sewers, either
through storage or managed infiltration to the ground. However,
increased intensity of rainfall events, as a potential consequence of
climate change, may demand greater capacity for temporary storage and
release of surface water, particularly in flood susceptible areas.
2.1. London’s groundwater system
London,
a megacity with significant historical legacy having undergone multiple
phases of development, makes an excellent case study for evaluating
urban groundwater systems and accounting for future change. It is
located in the estuary of the River Thames catchment with the Chalk
aquifer, the most important aquifer within the UK (MacDonald and Allen, 2001),
lying at depth beneath the city. The aquifer is covered and confined by
clays with interbedded sand and gravel deposits. These overlying
deposits afford a degree of protection to the Chalk aquifer as well as
providing a small component of additional resource from the more
permeable granular deposits. The Chalk aquifer in London has been
significantly exploited for public and industrial supply since the 1850s
and is one of the most monitored and managed aquifer-systems in the UK (Royse et al., 2012). The ready supply of groundwater in London has been an integral part of its industrial development (e.g. Wilkinson, 1985); similarly changes in industry are reflected in fluctuations in water demand and water resilience (groundwater resource, energy, hazard and ecosystem services).
Here
we systematically try to capture the current baseline for London (water
supply and utility, built environment, energy, ecosystem services and
hazard), whilst recognizing
the significance of the historical industrial development to this
baseline. So whilst London does make a good case study for cities that
have experienced multiple phases of development, it represents one of
the most historic urban developments in the world. Therefore, a unique
set of circumstances prevail that make urban planning particularly
difficult in terms of changes in land use and transition
through secondary and tertiary industries, which results in competition
for subsurface space, legacy contaminants and heavily exploited natural
resources in an area of heterogeneous ground conditions.
2.1.1. Water supply and utility
Privatisation
of water supply in the UK has resulted in the formation of twenty four
water companies. TWUL is responsible for the provision of water to the
London area and five other water resource zones to the west of London.
TWUL serves over 13.5 million customers in London and the Thames Valley (TWUL, 2015).
Within the broader River Thames catchment within which London lies, 80%
of public water supply comes from groundwater and 20% from surface
water sources, while the reverse is true in London where 20% of public
water supply comes from groundwater. Whilst direct groundwater
abstraction for public water supply in London is low, the baseflow index
(BFI) for the River Thames at Kingston (Thames tidal limit) is 0.63 (NFRA; gauging station 39001—period of record 1883–2014),
indicating that 63% of the river flow is derived from groundwater. This
demonstrates the indirect contribution of groundwater from the wider
river catchment to support London’s surface water abstraction.
With
a rising population that uses an increasing volume of water per head,
in conjunction with climate change projections, London is facing an
increasing water supply deficit, projected to rise from 59.4 Ml/d in 2015–415.9 Ml/d in 2040 (TWUL, 2015).
As well as emphasising the requirements for leakage detection and
repair, this increasing deficit requires the sourcing of additional
resources, which includes artificial recharge schemes, e.g. the North London (Enfield-Haringey) and South London (Merton, Streatham) artificial recharge schemes (Jones et al., 2012; O’Shea and Sage 1999; TWUL, 2015).
Abstraction and recharge for these schemes is typically not balanced.
For example, at the North London facility abstraction reaches up to
10981 Ml/yr but typically has been less than 5000 Ml/yr in recent years. In contrast artificial aquifer recharge at the sites reaches quantities of up to ∼4000 Ml/yr but has been negligible in recent years.
Water
supply and demand reduction in the short to medium-term is being driven
through a combination of leakage reduction, progressive metering and
water efficiency measures (TWUL, 2015). However whilst leakage from the pipe network is 665 Ml/d, equivalent to 25% of the total water demand (2014/15; TWUL, 2015)
the Economic Level of Leakage has been reached i.e. the level at which
the cost of further reducing leakage exceeds the cost of producing water
from an alternative source (DEFRA, 2008; TWUL, 2015).
The water deficit is also increasingly being met through increasing the
hinterland for groundwater supply, i.e. through trading with other
water companies such as Essex and Suffolk Water and RWE N-Power and
identifying new resource options. The first water desalination plant in
the United Kingdom, the TWUL Desalination Plant, or Beckton Desalination
Plant was built in Beckton, in the London Borough of Newham in east
London for TWUL at a cost of £250 million (Water Technology, 2016). It was opened on 2 June 2010 and provides up to 150 Ml/d. This is enough for nearly one million people in north-east London. Consideration is also being given to new wastewater re-use schemes, e.g. two wastewater reverse osmosis re-use plants are planned: Deephams recycling 60 Ml/d in 2027 and Beckton recycling 100 Ml/d in 2032 (TWUL, 2015). However the problems of emerging contaminants e.g. pharmaceuticals (Stuart et al., 2012) have to be considered in the evaluation of these schemes.
Water
for public supply is the primary consumptive use of abstracted
groundwater under licence in London (80%), with non-consumptive
groundwater abstraction licences for ground source heating and cooling
systems also increasing across the city (Environment Agency 2015).
Proportionally about half of TWUL’s supply is for household use, a
quarter is lost through leakage and just 20% is used for non-household
purposes (TWUL, 2015).
2.1.2. Built environment
London’s
subsurface is host to an increasing density of infrastructure such as
transport tunnels, requiring dewatering schemes to control groundwater
during their construction (Royse et al., 2012).
Conflicting demands and restrictions on underground space render it
necessary to take such infrastructure to increasing depths, e.g. at the
time of construction (2010) the Lee Sewerage Tunnel was the deepest
tunnel in London, exceeding the depth of the deepest underground station
Hampstead (58.5 m) by 20 m. Whilst this depth may not seem significant when compared with the Gotthard Tunnel (Simoni, 2013), which is 2.3 km
under the Alps at its deepest point, construction beneath London is
difficult because of the weak nature of the ground and the requirement
to manage the groundwater conditions. Engineering in London is made even
more difficult by rising groundwater levels, which result from
reductions in water demand by industry (Fry, 2009; Lucas and Robinson, 1995; Wilkinson, 1985).
The
demands for urban space, accompanied by a relaxation in planning
constraints, have resulted in a proliferation of basements, which impact
on natural recharge and impede shallow groundwater, thereby lowering
resilience to flooding e.g. the London Borough of Kensington and Chelsea
received 450 applications for basements in 2013. To help address this
local planning policy in parts of London restrict basement size to 50%
of the garden to protect “the character and function of gardens, allow
flexibility in planting and natural surface water drainage” (RBKC, 2014).
The urban flooding issue is complex and has been compounded by rising
groundwater levels in the Chalk aquifer in central London following
reductions in groundwater abstraction after industrial decline (Fry 2009; Lucas and Robinson, 1995) and the historic culverting of the surface water system (Barton, 1992).
Rising groundwater levels have been addressed and are now stabilized
through a collaborative groundwater abstraction operation led by the
environmental regulator, TWUL and London Underground. Meanwhile broader
flooding issues are being addressed through the Greater London Authority
Drain London programme, a partnership of 33 London boroughs, the Environment Agency, TWUL and Transport for London, which is aimed at better prediction and management of surface water flood risk in London.
The
consequences for groundwater of construction in the subsurface are
multi-facetted and include: (i) partitioning of groundwater, thereby
altering natural flow paths, which adds complexity to groundwater modelling;
(ii) increasing vulnerability due penetration of the confining layer
which affords protection to the groundwater quality; (iii) the networks
of transport, energy and fluids all have the potential to leak
contaminants; (iv) the networks of transport, energy and fluids have the
potential to take up groundwater through any ruptures; (v) as
construction moves deeper into the subsurface dewatering imposes a
greater potential for groundwater mixing with the potential for
reductions in groundwater quality. Such consequences demand increasingly
technical and more robust solutions to meet the resilience requirements
of the city’s growing population. New technologies are emerging to
achieve this, e.g. the use of robots to repair underground pipes (Hollingum, 1998) and geophysics for pipe leak detection (Kuras et al., 2016).
The extent of groundwater abstraction can be monitored from the induced
ground level change, seen in remotely sensed radar interferometry (e.g.
Cigna et al., 2015; Boni et al., 2016; Pratesi et al., 2016).
2.1.3. Ecosystem services
The
multiple functions that ecosystem services provide with respect to the
ground beneath urban areas are increasingly being recognized by city
practitioners. For example groundwater provides multiple services,
primarily for potable water supply but also by diluting and attenuating
contaminants and by acting as a medium for exploiting ground heat.
However, appropriate assessment and management of ecosystem services
provided by the ground are less clearly understood. There are more than
40 active ground source heating and cooling systems utilising
groundwater in central London, including those used by London
Underground where groundwater pumped from Victoria Station as part of
the station’s dewatering system is used to cool the platform. It is
estimated that up to 19% of London’s total heat demand (2010) could be
derived from ground heat sources (GLA, 2013). Despite the opportunity, rising groundwater temperatures are already a concern with a 2 °C rise in temperature between 2005 and 2014 recorded in parts of London (Environment Agency, 2015).
Groundwater
is also influenced by other ecosystem services provided in urban areas.
For example, to facilitate natural recharge, sustainable drainage
systems have been promoted and incorporated as local planning policy for
London. A drainage hierarchy is adopted, whereby storage of rainwater
for subsequent use, natural infiltration systems and attenuation of
water are to be considered in preference to direct discharge of water to
water courses and combined sewers. Whilst sustainable drainage systems
have the benefit of increasing natural groundwater recharge, enhancing
urban ecology and attenuating contaminants in surface water, if not
installed in appropriate locations they may increase local groundwater
flood risk, cause dissolution of soluble rocks and mobilize contaminants
present in soils and the shallow subsurface unsaturated zone (Dearden and Price, 2012). Additionally, they may disrupt natural filtration and geochemical processes operating in the subsurface.
3. Future city interventions
Commonly,
environmental challenges in cities are a construct of multiple social
and political dynamics. For example, low environmental standards are not
merely problems of human behaviour, caused by collective human and
political actions, but of their underlying interests, beliefs, and
values as well (Koger and Winter, 2010).
Conversely, collective creative management of the urban environment
across industry domains, can deliver improved human well-being, leisure,
recreational and biodiversity benefits (Rachwal et al., 2014). As we transition
to a desirable, but sustainable future state, and tackle these
environmental challenges, a range of different interventions or measures
will be implemented by various city actors, for different purposes that
will have complimentary and competing objectives. Urban planners,
working collaboratively with experts across environmental, social,
economic and political domains have a critical role in shaping the
necessary conditions that deliver positive outcomes for both urban
environments and communities. In consideration of the relationship
between water and cities, Rachwal et al. (2014)
construct five nonexclusive visions of how communities might
potentially tackle the issue of integrated water management. The visions
embrace the role of sensitive urban design, green landscapes and
nature-based solutions, sensors and system efficiencies, in addition to
citizen participation and sustainable habits, each of which has a
bearing on the urban groundwater system. However, their vision of
‘Cities and the Underworld' deals directly with groundwater systems and
highlights a future where infrastructure is increasingly built
underground in cities and the subsurface is more effectively managed to
deliver effective drainage, water storage,
heating and cooling. These concepts are in keeping with recent research
which highlights the benefits of modern urban innovation and policy,
for example, growing investment in smart utilities and digital
technologies (Angelidou 2015), conjunctive use of alternative water storage and water re-use options (Dillon et al., 2006; Hunt et al., 2013; Rojas-Torres et al., 2014), decentralized water supply systems (Chen et al., 2010) and green infrastructure and sustainable urban drainage (Chow et al., 2014; Dearden and Price, 2012).
In addition to the anthropogenic influences described in Table 1,
the following urban interventions have a potential influence on urban
groundwater systems: use of marginal groundwater, aquifer storage and
recovery, sustainable drainage systems, urban greening, rainwater
harvesting, wastewater recycling, household water efficiencies, smart
metering and sensor technologies, pipe leakage reduction and ground
source heating systems. These interventions are described further in Table 2
and represent measures for which a simple semi-quantitative assessment
of their impact can be undertaken using existing research outcomes and
openly available data. Though not an exhaustive list, these
interventions cover a mix of measures provided by different city
organisations which significantly affect water supply and demand,
behavioural change and new technologies.
Table 2. Interventions used for the groundwater accounting exercise discussed in this paper.
| Intervention | 2036 Future Vision: Strategic London | 2036 Future Vision: Aspirational London | Responsible organisations (UK) | |
|---|---|---|---|---|
| Supply | Rainwater harvesting | All new homes in London are fitted with rainwater harvesting systems. | All suitable roof space in London is used for rainwater harvesting systems. | Home builders |
| Citizens | ||||
| Aquifer storage and recovery | All currently planned artificial recharge (AR) and aquifer storage and recovery (ASR) schemes are implemented utilising storage in the chalk aquifer. | All currently viable artificial recharge (AR) and aquifer storage and recovery (ASR) schemes are implemented. Additional sites for ASR and AR are sought. | Water company | |
| Environmental regulator | ||||
| Wastewater recycling (effluent re-use) | Currently planned wastewater recycling scheme is implemented. | A second wastewater plant is developed, in preference to a new reservoir and water transfers in keeping with public opinion and net present value (TWUL, 2015). | Water company | |
| Leakage reduction | Pipe leakage is reduced by 16% in line with targets planned by the water company. | Pipe leakage targets are doubled, as a result of pressure from the public, despite the economic leakage level. Hydraulic engineering to reduce leakage is considered. | Water company | |
| New groundwater borehole supplies | Currently planned new groundwater borehole supplies are constructed. | No further groundwater sources are developed, as water recycling is preferred. Research into ‘marginal’ groundwater sources is on-going. | Water company | |
| Environmental regulator | ||||
| Water transfers | Planned water transfers into London remain in place. | Water transfers into and out of London’s water supply area are stopped. | Water company | |
| Greywater recycling | Grey-water recycling is installed as standard in all new homes in London. | All homes in London are retrofitted with grey-water recycling systems. | Home builders | |
| Infiltration sustainable drainage systems (SuDS) | SuDS are installed to reduce the volume of surface water flowing into the combined sewer network in London. | Infiltration SuDS are installed across 10% of London land area where run-off rates are high and infiltration SuDS are suitable. | Local authority | |
| Home builders | ||||
| Landscape architects | ||||
| Demand | Smart Home – water efficiency | All new homes in London are fitted with water saving devices. | All of London’s homes are retrofitted with water saving devices. | Home builders |
| Designers and architects | ||||
| Citizens | ||||
| Water company | ||||
| Smart water meters | 735,000 homes in London have water meters installed in line with water company targets. | All of London’s homes have a water meter installed. | Water company | |
| New water tariffs and behaviour change | Planned activities to encourage behaviour change are effective and new tariffs are introduced. | Behaviour change brings London’s per capita water consumption in line with the national average (150 l/person/day). | Water company | |
| Water company Citizens | ||||
| Neutral | Groundwater sourced heating systems | Groundwater source heating systems utilising London’s aquifers continue to be installed in line with current trends. | Groundwater source heating is actively promoted as a low carbon energy source and the installation rate of new systems doubles. | Environmental regulator |
| Home builders | ||||
| Designers and architects | ||||
4. Future visions for London
London covers 1595 km2,
is home to over 8.5 million people and is one of the largest
metropolitan economies in the world. By 2036 London's job market is
expected to grow to 5.8 million jobs from 4.9 million in 2011 and an
additional ∼1 million households will be accommodated over the same
period (GLA, 2015). In parallel significant investment in infrastructure, of the order of £1.3 trillion, is anticipated by 2050 (Mayor of London, 2014).
Whilst much of this investment is allocated for transport and housing,
investment in water infrastructure (4%) and green infrastructure (2%) is
accounted for and ambitions for a 10% increase in urban green space
have been outlined (Mayor of London, 2014).
London
is located in a water-stressed region in the southeast of England and
already experiences water-deficits during dry years (TWUL, 2015). By 2036 London’s population is projected to exceed 10 million (GLA, 2015), increasing water demand
by approximately 16%. Pressures on water availability within the river
Thames catchment will be compounded by climate change with storm events
and climatic extremes expected to dominate. At present 15% of London,
1.5 million people and 480,000 properties lie within the floodplain of
the Thames and its tributaries (GLA, 2015).
By 2050 winter rainfall is predicted to increase by 14% with an
associated increase in river flows of approximately 13%, meanwhile
summer rainfall is predicted to fall by 19% leading to a reduction in
summer river flows of 15% (Prudhomme et al., 2012; Haxton et al., 2012).
These effects are potentially very significant for London given its
high reliance on surface water and groundwater baseflow. TWUL currently
expect the effects of climate change to reduce water availability by
approximately 72 Ml/d (TWUL, 2015)–equivalent to the daily water demand of over 400,000 Londoners.
London’s
future water resource situation is dictated not only by changes in
climate and the natural systems but also by the anthropogenic
activities, described earlier, that act on or intervene with it. As we
tend towards a more desirable sustainable future, a series of measures
or interventions will be put in place, by various stakeholders in London
to deliver on agreed social, environmental and economic goals. There is
a need to consider the ways in which the proposed interventions may
interact with other city systems and the extent to which undesirable
outcomes or complimentary benefits may occur (e.g. Price et al., 2016).
This point is illustrated by considering how groundwater systems might
be affected by the implementation of a range of city interventions in
London. To assess the extent to of these effects two contrasting visions
for London have been selected and simple groundwater accounting
undertaken for a range of future city interventions (Table 2).
The aim of the accounting exercise is to calculate, across the London
water supply area, the effect that different city interventions have on
the urban water balance and to identify which elements of the urban
groundwater system are disturbed as a result. Hydrometric data,
geospatial data and water supply information embedded within water
resource management plans and urban strategic plans are used in
combination to perform the semi-quantitative analysis. For example, TWUL
uses industry standard methodologies to forecast future demand taking
into account population (an increase of 2.0–2.9 million people by 2040
with 75% forecast in London); property projections; water use data and
trends to forecast how the components of demand for water are likely to
vary over the next 25 years (TWUL, 2015). Further information about the data sources and assumptions are provided in Table 3.
The impact of the interventions is expressed in megalitres per day
(Ml/d) and as a proportion of i) London's predicted water demand in
2036, and ii) London's predicted groundwater recharge in 2036.
Table 3. Groundwater accounting results.
| Interventions | Effect on urban water cycle | Future Vision for 2036 | Total change in water balance (Ml/d) | % of London’s water demand in 2036 | % of London’s groundwater recharge in 2036 | Source data and assumptions | |
|---|---|---|---|---|---|---|---|
| Supply | Rainwater harvesting | Rainwater that would otherwise go to surface water drains (or into the ground) is intercepted and held in storage for onward use in the home. The volume of treated water distributed to the home is reduced, increasing water availability. | Strategic | 39.9 | 1.8 | 13.0 | Future Water (2008). TWUL Final WRMP 2015–2040 Appendix E. GLA (2008). |
| Aspirational | 80 | 3.7 | 26.0 | Assumptions: 28.29 Ml/d of rainwater can be obtained per person per home. | |||
| Rainwater tanks provide sufficient storage to ensure daily water needs during dry periods. | |||||||
| Wastewater recycling (effluent re-use) | Domestic wastewater is treated centrally by the water utility and recycled for domestic use. The volume of wastewater being discharged to rivers and seas is reduced. | Strategic | 150 | 6.9 | 48.7 | TWUL Final WRMP 2015–2040 Exec summary. | |
| Aspirational | 300 | 13.8 | 97.4 | Assumption: Under an aspirational future invested is diverted towards wastewater recycling and away from the development of a new reservoir which is in keeping with public perception (London 2036) and cost-benefit analysis (TWUL Final WRMP Exec summary). | |||
| Greywater recycling (internal household water recycling) | Demand for treated water in the home is reduced, increasing water availability. | Strategic | 67.3 | 3.1 | 21.9 | Hunt et al. (2013). TWUL Final WRMP 2015–2040. | |
| Aspirational | 419.6 | 19.3 | 136.2 | Assumption: Greywater recycling within domestic homes delivers a 25% water saving. Its assumed that either rainwater harvesting or greywater recycling technology would be installed not both. | |||
| AR (Artificial recharge) ASR (Aquifer storage and recovery) | Spare storage in London's aquifers, where groundwater levels are low, is used to store surplus water for later use increasing water availability in times of shortages. | Strategic | 23 | 1.1 | 7.5 | TWUL Final WRMP 2015–2040 Executive Summary and Appendix R. | |
| Aspirational | 26 | 1.2 | 8.4 | Assumptions: TWUL explored all aspirational ASR and AR sites in their options appraisal. | |||
| Sustainable drainage implementation | The volume of surface water going to piped drainage is reduced, reducing the risk of storm ‘overflows' and pollution. Natural urban groundwater recharge is increased. The volume of water held in surface water storage increases. | Strategic | 87 | 3.9 | 28.3 | BGS Infiltration SuDS Suitability Map (Dearden et al., 2013). BGS Thames Run-off − Recharge Model (Mansour and Hughes, 2004). HR Wallingford SuDS tool (HR Wallingford 2016). | |
| Aspirational | 282 | 13 | 91.6 | Assumptions: 1 in 1 year estimated discharge for a 1 ha site in London suitable for infiltration SuDS is 2.5 L per second. Sites have 25% open area, i.e. 75% of land needs to be drainage at greenfield run-off rate. London’s development rate is 0.5% of land per year, meaning 10% of land is developed by 2036. | |||
| New groundwater sources | More water is available for public supply as new abstraction wells are drilled. Groundwater available to support groundwater dependent ecosystems is reduced. Groundwater levels are lowered near to the well. | Strategic | 17 | 0.8 | 5.5 | TWUL Final WRMP 2015–2040. | |
| Aspirational | 0 | 0 | 0 | Assumption: Under an aspirational future additional groundwater abstraction is to be minimized. | |||
| Leakage reduction | The amount of treated water and wastewater that leaks from the pipe network is reduced. Contamination of groundwater by wastewater is therefore reduced but so is urban groundwater recharge. | Strategic | 109 | 5.0 | 35.4 | TWUL Final WRMP 2015–2040 Exec summary. | |
| Aspirational | 218 | 10.0 | 70.8 | Assumptions: Under an aspirational future leakage reduction doubles despite the fact that the economic leakage level has already been reached. | |||
| Demand | Smart Home – water efficiency | Demand for treated water in the home is reduced and therefore less waste water needs to be treated. Capacity in the sewer network is increased and the risk of ‘overflows' and pollution events is reduced. | Strategic | 238 | 10.9 | 77.3 | Future Water (2008). TWUL Final WRMP Appendix E. |
| Aspirational | 590 | 27.1 | 191.6 | Assumptions: Installation of water saving devices receives public acceptance and volumes of water saved are in line with predictions. | |||
| SMART meter installation | Demand for treated water in the home is reduced and therefore less waste water needs to be treated. Capacity in the sewer network is increased and the risk of ‘overflows' and pollution events is reduced. | Strategic | 38 | 1.8 | 12.3 | TWUL Final WRMP 2015–2040. | |
| Aspirational | 208.8 | 9.6 | 67.8 | Assumptions: The water saving delivered by water meters is linearly scalable with the number of meters installed. In reality greater water saving will be delivered by those who opt for water meters compared to compulsory metering (ref). | |||
| New water tariffs and behaviour change | Demand for treated water in the home is reduced and therefore less waste water needs to be treated. Capacity in the sewer network is increased and the risk of ‘overflows' and pollution events is reduced. | Strategic | 62 | 2.9 | 20.1 | TWUL Final WRMP 2015–2040. | |
| Aspirational | 170.9 | 7.9 | 55.5 | Future Water (2008). Mayor of London (2011). | |||
| Assumption: Proposed activities receive public acceptance and deliver predicted water savings. | |||||||
| Neutral | Groundwater sourced heating | There is no net change to the urban water balance as water is recirculated between the ground and the homes heating system but groundwater temperatures increase locally and regional groundwater temperature increase by over 2 °C. | Strategic | 118 new sites. | No net change | No net change | Environment Agency (2015) |
| Aspirational | 338 new sites. | No net change | No net change | Assumptions: The chalk aquifer can deliver the heating and cooling demand required from the projected increase in ground source heating systems under both the strategic and aspirational visions. | |||
The
first vision, referred to as ‘Strategic 2036’ sets out a future for
London guided by strategic plans and policy information provided by the
organisations with responsibility for planning London’s future, e.g. the
local authority, water provider and environmental regulator. In
essence, this scenario provides a projection of a likely future state
should the organisational objectives for London in 2036 be implemented
as planned. Current operational and business needs dominate in this
vision.
The second, referred to as ‘Aspirational
2036’, provides a future vision for London which goes beyond the city
strategic plans and adopts a desirable but plausible sustainable future.
Under this vision, in line with the Urban Futures new sustainability
paradigm (Rogers et al., 2012),
resources are used sustainably, social responsibility dominates and
citizens are engaged. This vision also embodies a more idealistic,
innovative and open approach in keeping with the notion of visioning
exercises (Wiek and Iwaniec, 2014).
These
two visions were chosen to highlight the potential disparity between i)
strategic plans developed by individual organisations that are guided
by operational needs and short-term business models, and ii) a future
which is still plausible but unconstrained in the way that city
interventions are implemented to transition
to a sustainable urban future. That is, the visions contrast a
projected future and a desirable future. A description of the various
interventions included within the groundwater accounting exercise, under
a strategic and aspirational future vision for 2036 is provided in Table 2.
5. Results: groundwater in London 2036
The results of the groundwater accounting exercise for the future city interventions are summarized in Table 3.
The interventions are categorized into those which affect the
availability of supply, those which affect demand for water and those
which have a neutral impact on water supply. The water balance is also
presented graphically, for both future visions, in Figs. 1 and 2
to highlight the extent to which the individual components of the urban
water cycle are affected by the selected future city interventions.
Fig. 1. An annotated urban water cycle showing the results of the accounting exercise for a strategic future.
Fig. 2. An annotated urban water cycle showing the results of the accounting exercise for an aspirational future.
5.1. Strategic future 2036
Under a strategic future for 2036 the greatest water-saving gains, as a percentage of London’s water demand, would be made through the construction of smart homes (10.9%) and the development of wastewater recycling
technologies (6.9%). These are also positive interventions with respect
to groundwater as smart homes and wastewater recycling both reduce
demand for water, reducing pressure on groundwater supplies.
Furthermore, water discharged to foul sewers is also reduced under this
scenario reducing the risk of sewer water overflows into natural water
systems. Groundwater recharge is not reduced.
5.2. Aspirational future for 2036
Under
an aspirational future for 2036 the greatest water-saving gains, as a
percentage of London’s water demand, would be delivered through the
construction of smart homes (27.1%) and installation of greywater
recycling (19.3%). Wastewater recycling is also capable of delivering
significant gains. As with the strategic future vision, both of these
interventions deliver positive benefits for groundwater systems through,
demand reduction and water recycling, with pressure on groundwater
supplies reduced and groundwater recharge unaffected.
5.3. Disparity between strategic and aspirational
The
level of disparity between a strategic vision and aspirational vision
for 2036 is evaluated, that is, where organisational policies are out of
line with what is achievable under a more aspirational sustainable
future. The greatest disparity is observed for both smart homes and
greywater recycling, where organisational policy for these interventions
falls short and a further 16% of London’s water demand could be found
through each of these interventions if more aspirational targets were
set. Organisational ambitions for the implementation of sustainable
drainage systems and water meters also fall short of what is plausible,
where an additional 9% and 8% of London’s water demand respectively
could potentially be if more proactive initiatives were implemented.
5.4. Implications for urban groundwater systems
A
number of future city interventions included in the accounting exercise
have a direct bearing on groundwater systems. For example the direct
withdrawal of groundwater through the development of new extraction
wells and the utilisation of aquifer storage through artificial recharge
schemes (ASR). Traditionally we might expect these schemes to have the
greatest impact on the urban groundwater balance.
Under both the strategic and aspirational visions for London 2036, the
development of new groundwater sources and ASR schemes has a minimal
impact on groundwater systems compared with other interventions (i.e.
∼2% of London’s water demand). Other interventions have a more indirect,
but potentially significant effect on groundwater systems. For example,
rainwater harvesting and pipe leakage reduction both serve to reduce
urban recharge to aquifers while infiltration
SuDS are designed to enhance groundwater recharge to urban aquifers.
Under a strategic vision for 2036, rainwater harvesting would
potentially reduce recharge to urban aquifers by up to 13%, though
arguably a significant proportion of rainfall is currently lost to
surface water drains and does not contribute to aquifer recharge, and
leakage reduction could reduce urban recharge up to ∼35%; meanwhile
infiltration SuDS may increase urban recharge by 28.3%, the net effect
being a reduction in recharge of ∼20%. Under an aspirational future
there is a less significant net effect on urban recharge (<5%) as
increased groundwater infiltration is delivered through greater
implementation of sustainable drainage systems.
6. Discussion
Applying
a groundwater accounting exercise to plausible cities interventions
provides semi-quantitative scenario analysis of aspirational urban
futures. Primarily an insight is gained as to the expected extent of
disturbance to groundwater stocks and flows that might occur as a result
of fulfilling the city’s ambitions. It has the distinct advantage over
traditional groundwater balancing, in that it considers not only the
direct groundwater processes (e.g. recharge, interflow, discharge) but
also the ways in which these processes are coupled to other
anthropogenic activities (e.g. surface sealing, construction) and
behaviours (e.g. water saving, policy development). As a result, a more
holistic evaluation of urban groundwater management can be defined. For
example, based on disturbance to groundwater systems should future
investment in water infrastructure be focused on increasing supply or
reducing demand? Equally, it is possible to evaluate whether the most
positive interventions from a groundwater perspective will be delivered
through new technologies or by a change in people behaviour and whether
there is an over-reliance on organisational policy and practice and an
under investment in private enterprize and innovation.
Considering urban groundwater systems in isolation, there is significant merit in adopting wastewater recycling
and greywater recycling technologies in combination with smart home
water efficiency and water meters, as measures to meet London’s
projected water resource demand. These interventions have the potential
to deliver significant benefits under both strategic and aspirational
futures. They also reflect a balance between the development of new
water recycling technologies to increase supply in parallel with
modification of people behaviour to reduce water demand
and consumption. These options are also economically favourable in
terms of the net present value calculated by the water supplier (TWUL, 2015).
Controversially,
from a groundwater perspective, leakage reduction might be discouraged
as it is likely to lead to a significant reduction in urban recharge,
though there are inevitable water quality concerns associated with
leakage from sewage pipe networks. Groundwater recharge modelling under future climate scenarios (Haxton et al., 2012)
suggests that the volume of water lost from pipe network through leaks
is equivalent to ∼35% of London's total groundwater recharge in 2036.
Even under an aspirational future, the level of groundwater recharge
delivered through infiltration
SuDS is unlikely to be sufficient to deliver an equivalent volume of
recharge to urban aquifers that is lost if pipe leakage is reduced to
zero.
However, we must not consider groundwater in isolation but in combination with economic assessments and public acceptance. Kirkpatrick and Smith (2011)
show, for aging cities in the US, that public water infrastructure
works are funded independently of city budgets such that key
infrastructure decisions are often far removed from community sentiment.
Under both a strategic and aspirational futures, the greatest water
gains can be delivered through the introduction of water-saving
technologies in smart homes–noting that this also has a positive effect
on groundwater systems. This sentiment is echoed by Newton and Meyer (2013)
in their discussion of water use, that “individual and household
behaviour changes offer the potential for a much faster rate of
sustainability transformation
than supply-side technological innovation of key infrastructures and
services”. Significantly though, there is the greatest disparity between
the strategic future and aspirational future for smart home
water-saving, suggesting that current and projected organisational
practice falls someway short of the potential for change. Here then we
can start to consider the organisational and behavioural constraints
that are limiting in-home water saving. For example, there is currently
no policy driver for installing water-saving technologies in new homes
and a heavy reliance on home-builders to drive uptake in new builds.
Moreover, London’s water provider has rejected retrofitting domestic
properties with modified toilet cisterns
and showerheads and enforced use of water efficiency measures in new
buildings on the grounds that the costs and benefits cannot be modelled
by comparison with alternative water management options (TWUL, 2015).
This is largely a result of high uncertainty that, given the heavy
reliance on modified people behaviours, these technologies will deliver
the predicted water-savings once installed.
The influence of people’s behaviour in the uptake and use of water-saving technologies is an important consideration in water utility (Hunt et al., 2013).
While there are many environmentally minded citizens, the environment
is not a major motivator for water conservation. Appeals to
environmental values when asking people to change their water-use habits
are unlikely to succeed on their own as they are often outweighed by
barriers such as lifestyle factors (Ministry for the Environment, 2009). Selby (2011)
argues that in many cultures water usage is not just a product of
climate but reflects the social and political ideals, for example
maintaining private lawns and gardens, and perceived levels of hygiene
and cleanliness (Kooy and Bakker, 2008).
Additionally, water provision is seen by some as a fundamental human
right and plans to curtail water use may be viewed as a challenge to
social justice and equity (Ministry for the Environment, 2009). These ideas driven by political distinctiveness and social standing are difficult to challenge and overcome (Selby, 2011).
Wiek and Iwaniec (2014)
draw attention to more sophisticated visualization techniques and
gaming approaches such as 3D visuals and immersive experiences to
encourage people to participate in visioning exercises. These
gaming-models (e.g. SimCity) allow a more systemic vision to be created
by participants where interconnected systems and dynamic feedbacks can
be presented (Wiek and Iwaniec, 2014).
In this way people can understand how their actions and goals relate to
and affect each other. Though not a controlled visioning exercise, such
an approach was adopted by the Future Cities Catapult, the UK's
Government-funded enabler of urban innovation. Using an interactive
gaming-model, questions on water resources, housing and transport were
posed to members of the public to provide integrated systematic insights
into the public’s aspirations for London’s future in the year 2036.
Each participant was provided with a forecasted future for London unique
to their answers which evaluated water availability, carbon emissions,
housing levels and transport capacity, thus allowing participants to
reflect on the implications of their responses. As well as providing
participants with individual feedback on future scenarios, results from
the gaming-models provide an informal insight to assess public
acceptance of new initiatives and policy decisions for London. It also
provides an opportunity to review people’s perceptions on London’s
future against the strategic and aspirational futures mapped out for
London in 2036.
Over a four-month period more than
15,000 people played the London 2036 gaming-model, of these participants
a third failed to implement measures to meet London’s forecasted water
demand. Additionally and equally concerning for groundwater
practitioners are respondents’ views on urban infrastructure, a clear
preference for both increased subterranean rail networks and high rise
buildings would result in greater disturbance to, and greater need for
protection of shallow groundwater systems in London. Despite these
outcomes, prospects for water management and water-saving options are
generally positive with respect to the urban groundwater system. 80% of
participants indicated a preference for waste water recycling (also
favourable under both the strategic and aspirational futures presented
here) over importing water from the hinterland. Meanwhile there was
clear inclination for rainwater harvesting (48.5%) over leakage
reduction (36.5%), new reservoirs (10%) and reduction of water exports
from the catchment (5%) as a means to increase water availability, and
equally there was support for water metering and in-home water saving
devices to reduce water demand. These results suggest that people are
generally open to the idea of innovative approaches to urban water
management and perhaps it is organisational policy and practice that is
more of a barrier to implementation. However, implementation of novel
water efficiencies, re-use and decentralisation of water systems, e.g.
as proposed by Rachwal et al. (2014)
in their water and cities vision, requires people in the UK to be
active water managers, rather than passive consumers. Given that a
plentiful and uninterrupted water service is already established and
remains an operational requirement there exists a challenge to motivate
people to be active managers of water when a passive attitude delivers
what is needed.
Semi-quantitative scenario
forecasting and more qualitative insight assessments provide useful
mechanisms to evaluate city visions, but there exist a number of natural
and anthropogenic interventions and influences that remain difficult to
account for, e.g. changes in climate and localized weather patterns,
rates of development and ground disturbance and population changes.
Understanding the uncertainty of these pressures and the potential
impacts requires not just future scenarios forecasting but predictive
modelling. Implementation of integrated and linked modelling approaches
such that multiple processes can be considered in tandem is increasingly
being employed for integrated water management (Heinz et al., 2007) and presents the opportunity for linked physical and socio-economic modelling of city visions.
7. Conclusion
Visioning
exercises are increasingly being used in cities to define desirable
future states, to create a shared vision that cuts across technical and
social spectrums, and which acknowledges the physical city constraints
whilst still being ambitious. As cities attempt to trend towards a more
sustainable urban future, visioning exercises may be used as a tool to
evaluate environmental challenges and innovative solutions against urban
futures. At present however, sustainability principles and the natural
environment tend to be lacking in city visions with a focus on the built
environment instead.
For environmental
considerations to be better captured in city visions we need to consider
the city in the context of its connected resource catchment or
‘hinterland’, furthermore an integration of, urban metabolism approaches
completed by city-practitioners, and ecosystem service
assessments–completed by environmental experts, is needed. For this to
be implemented successfully a more-fluid approach to natural catchment
and political boundaries is warranted where boundary conditions are
instead guided by the dynamics of the system stocks and flows operating
across the rural-urban fabric.
Significant effort is being invested to map the pathways needed to transition
towards a desirable sustainable future and to enable the implementation
of urban innovations and city interventions to meet these aspirations.
Frequently, and particularly for water resource supply, the
interventions and future management plans are guided by individual
organisational needs and business demands. These planning exercises,
which are completed separately to visioning exercises, are robust but
they are constrained by operational practice, siloed, and not systemic.
There
is a growing body of evidence highlighting the importance of
groundwater to support urban living and the impact of urbanism on
natural groundwater systems however it is rarely considered in city
systems thinking. The groundwater accounting exercise employed here is
successful in highlighting the interconnections between groundwater
processes and other city systems; in doing so the potential benefits and
undesirable consequences of various city interventions on urban
groundwater systems are defined and can be evaluated against other
social and political considerations. For London, if a strategic future
guided by existing operational practice and organisational need were to
unfold, we would see preferential investment in industry-scale
technologies such as wastewater treatment and aquifer storage and
recovery. While these interventions deliver positives benefits under
both futures, acknowledgement that behaviour change offers the potential
for a faster rate of sustainability transformation than innovation technologies is ignored.
We
need to be guided by unconstrained ideas and innovation and encourage
more joint business and community enterprize and invite city
practitioners to inform the pathways to implementation that consider the
social context in addition to the environmental constraints and
business drivers. For London, adopting such an aspirational vision there
is greater opportunity to deliver benefits via community-led action
such as sustainable drainage and green infrastructure and in-home water
efficiency measures.
For more aspirational
urban groundwater interventions to be implemented in cities we need to
encourage more integrated, systemic and quantitative evaluation of the
likely pathways, interventions and interactions. This is increasingly
possible with the use of linked and integrated modelling where
groundwater process models, physical models and water industry
models can be coupled and inform socio-economic assessment, where the
value of water, in all its guises, is increasingly being recognized
(e.g. Barthel et al., 2005).
Throughout
the visioning exercises we need to be mindful that the plausible and
the possible are only achievable if there is public acceptance. In
tandem with more traditional predictive, quantitative groundwater modelling which allows for probabilistic forecasting, more-qualitative future scenario assessments is being advocated (GO-Science, 2016).
Such scenario development encourages greater participatory engagement
and unconstrained ideas, to support judgement-based, context-driven
future states. Such approaches are starting to be utilized by the water
resource sector and should be further-encouraged to develop more active
behaviours in water resource management by communities.
Acknowledgments
This study was carried out as part of a NERC knowledge exchange fellowship (NE/M020673/1)
held by S. Bricker undertaken in partnership with Innovate UK’s Future
Cities Catapult. The investigations were co-funded by the British Geological Survey’s Urban Geoscience research programme. Support from the Future Cities Catapult data lab
team through the London 2036 data exhibit is gratefully acknowledged.
The authors thank Henry Holbrook for provision of the illustrations and
artwork for the paper. Bricker, Banks and Tapete published with the
permission of the Executive Director of BGS-NERC.
