1,307 research outputs found
Simulation of the spatio-temporal extent of groundwater flooding using statistical methods of hydrograph classification and lumped parameter models
This article presents the development of a relatively low cost and rapidly applicable methodology to simulate the spatio-temporal occurrence of groundwater flooding in chalk catchments. In winter 2000/2001 extreme rainfall resulted in anomalously high groundwater levels and groundwater flooding in many chalk catchments of northern Europe and the southern United Kingdom. Groundwater flooding was extensive and prolonged, occurring in areas where it had not been recently observed and, in places, lasting for 6 months. In many of these catchments, the prediction of groundwater flooding is hindered by the lack of an appropriate tool, such as a distributed groundwater model, or the inability of models to simulate extremes adequately. A set of groundwater hydrographs is simulated using a simple lumped parameter groundwater model. The number of models required is minimized through the classification and grouping of groundwater level time-series using principal component analysis and cluster analysis. One representative hydrograph is modelled then transposed to other observed hydrographs in the same group by the process of quantile mapping. Time-variant groundwater level surfaces, generated using the discrete set of modelled hydrographs and river elevation data, are overlain on a digital terrain model to predict the spatial extent of groundwater flooding. The methodology is applied to the Pang and Lambourn catchments in southern England for which monthly groundwater level time-series exist for 52 observation boreholes covering the period 1975–2004. The results are validated against observed groundwater flood extent data obtained from aerial surveys and field mapping. The method is shown to simulate the spatial and temporal occurrence of flooding during the 2000/2001 flood event accurately
The development and validation of the object-oriented quasi three-dimensional regional groundwater model ZOOMQ3D
This report documents the modifications made to the object-oriented regional groundwater
model ZOOM2D (The University of Birmingham, 2001). Additional mechanisms are
introduced to this model to satisfy the generally-accepted functional requirements of a
commonly-applied regional groundwater flow model. The modified model, ZOOMQ3D, is
quasi three-dimensional and is validated through comparison with analytical solutions and with
instructional problems formulated for MODFLOW (McDonald and Harbaugh, 1988) by
Anderson (1993)
A lumped conceptual model to simulate groundwater level time-series
Lumped, conceptual groundwater models can be used to simulate groundwater level time-series quickly and efficiently without the need for comprehensive modelling expertise. A new model of this type, AquiMod, is presented for simulating groundwater level time-series in unconfined aquifers. Its modular design enables users to implement different model structures to gain understanding about controls on aquifer storage and discharge. Five model structures are evaluated for four contrasting aquifers in the United Kingdom. The ability of different model structures and parameterisations to replicate the observed hydrographs is examined. AquiMod simulates the quasi-sinusoidal hydrographs of the relatively uniform Chalk and Sandstone aquifers most efficiently. It is least efficient at capturing the flashy hydrograph of a heterogeneous, fractured Limestone aquifer. The majority of model parameters demonstrate sensitivity and can be related to available field data. The model structure experiments demonstrate the need to represent vertical aquifer heterogeneity to capture the storage-discharge dynamics efficiently
The development of linked databases and environmental modelling systems for decision-making in London
A basic requirement for a city's growth is the availability of land, raw material and water. For continued and sustainable development of today’s cities we must be able to meet these basic requirements whilst being mindful of the environment and its relationship with anthropogenic activity. The heterogeneous and complex nature of urban systems where there are obvious environmental and anthropogenic inter-dependencies necessitates a more holistic approach to decision-making. New developments such as linked databases of environmental data and integrated environmental modelling systems provide new ways of organising cross-disciplinary information and a means to apply this to explain, explore and predict the urban systems response to environmental change. In this paper we show how, accessibility to linked databases, detailed understanding of the geology and integrated environmental modelling solutions has the potential to provide decision-makers and policy developers with the science based information needed to understand and address these challenges
Reconstruction of multi-decadal groundwater level time-series using a lumped conceptual model
Multi-decadal groundwater level records, which provide information about long-term variability and trends, are relatively rare. Whilst a number of studies have sought to reconstruct river flow records, there have been few attempts to reconstruct groundwater level time-series over a number of decades. Using long rainfall and temperature records, we developed and applied a methodology to do this using a lumped conceptual model. We applied the model to six sites in the UK, in four different aquifers: Chalk, limestone, sandstone and Greensand. Acceptable models of observed monthly groundwater levels were generated at four of the sites, with maximum Nash–Sutcliffe Efficiency scores of between 0.84 and 0.93 over the calibration and evaluation periods, respectively. These four models were then used to reconstruct the monthly groundwater level time-series over approximately 60 years back to 1910. Uncertainty in the simulated levels associated with model parameters was assessed using the Generalized Likelihood Uncertainty Estimation method. Known historical droughts and wet period in the UK are clearly identifiable in the reconstructed levels, which were compared using the Standardized Groundwater Level Index. Such reconstructed records provide additional information with which to improve estimates of the frequency, severity and duration of groundwater level extremes and their spatial coherence, which for example is important for the assessment of the yield of boreholes during drought period
Groundwater drought forecasting using lumped conceptual models
For
fractured aquifers, such as the Cretaceous Chalk, autocorrelation
in SGI (Bloomfield & Marchant, 2013) has been inferred
to be primarily
related to autocorrelation in the recharge time series, while in granular
aquifers, such as the Permo–
Triassic sandstones, autocorrelation in
SGI is inferred to be primarily a function of intrinsic
saturated flow and
storage properties of aquife
Seasonal forecasting of groundwater levels in principal aquifers of the United Kingdom
To date, the majority of hydrological forecasting studies have focussed on using medium-range (3–15 days) weather forecasts to drive hydrological models and make predictions of future river flows. With recent developments in seasonal (1–3 months) weather forecast skill, such as those from the latest version of the UK Met Office global seasonal forecast system (GloSea5), there is now an opportunity to use similar methodologies to forecast groundwater levels in more slowly responding aquifers on seasonal timescales. This study uses seasonal rainfall forecasts and a lumped groundwater model to simulate groundwater levels at 21 locations in the United Kingdom up to three months into the future. The results indicate that the forecasts have skill; outperforming a persistence forecast and demonstrating reliability, resolution and discrimination. However, there is currently little to gain from using seasonal rainfall forecasts over using site climatology for this type of application. Furthermore, the forecasts are not able to capture extreme groundwater levels, primarily because of inadequacies in the driving rainfall forecasts. The findings also show that the origin of forecast skill, be it from the meteorological input, groundwater model or initial condition, is site specific and related to the groundwater response characteristics to rainfall and antecedent hydro-meteorological conditions
Assessing future flood risk at BGS and NERC observatory sites : summary report
UK Research and Innovation (UKRI) recognises the
problems posed by climate change, its impact on
society, and the need for positive action to address
the environmental sustainability challenges we
now face. By 2040, UKRI aspires to be ‘net-zero’
for its entire research undertaking, which includes
reducing and mitigating all carbon emissions
from UKRI owned operations (UKRI, 2020).
Surface water flooding can cause disruption to
people’s daily activities, businesses, and societal
functioning, consequently increasing the pressure
on natural resources. UKRI aims to understand
the risk of flooding to its properties to act where
possible to enhance climate resilience.
This Summary Report describes work undertaken
by the British Geological Survey (BGS) in
partnership with the Natural Environment Research
Council (NERC) to investigate the risk of flooding
to the BGS Keyworth and BGS Edinburgh sites,
and to four NERC observatory sites (at Capel
Dewi, Eskdalemuir, Hartland, and Herstmonceux).
Flood risk was assessed under both ‘current’
and ‘future’ climate conditions. After reviewing
existing assessments of the risk of flooding at
these locations, additional flood analyses and
modelling were undertaken for the sites that
have been mapped as being at risk of fluvial or
pluvial flooding. These sites are BGS Keyworth,
BGS Edinburgh, and the National Centre for
Atmospheric Science (NCAS) Capel Dewi
Atmospheric Observatory (CDAO). This report
summarises the findings from the analyses and
hydraulic modelling studies of the three sites. It is
accompanied by a second report, which provides
more detailed technical information (Nagheli et al.,
2022).
Flooding due to direct heavy rainfall (pluvial
flooding) or due to overflowing surface water
features (fluvial flooding) could cause water to
inundate areas of the sites investigated, potentially
resulting in business disruption and damage
to infrastructure. The risk of this is assessed by
evaluating whether a feature would be affected by
surface water or not, and if so, how often it would
be expected.
The UKCEH Flood Estimation Handbook (Institute
of Hydrology, 1999) methodology was used
to obtain profiles of rainfall over time for design
storms (see Glossary). The ReFH2 software (the
Revitalised Flood Hydrograph rainfall-runoff
method version 2; Kjeldsen, 2006) was used
to estimate the corresponding surface runoff
hydrographs for catchments above points of
interest.
The HEC-RAS flood modelling software (US Army
Corps of Engineers, 2022) was used to simulate
fluvial flooding. The SWMM modelling software
(Storm Water Management Model; US EPA. 2022)
was used to simulate pluvial flooding and to assess
the capacity of drainage infrastructure (for BGS
Keyworth only).
The assessment of how flood risk will change in
the future makes use of climate change ‘uplift’
factors. These factors have been used to shift
historical design storms. Uplift factors have
been estimated using the latest UK Met Office
Hadley Centre climate projections—the UKCP18
projections—by the UKRI-funded FUTUREDRAINAGE project (Chan et al., 2021). Factors
are only available for a ‘worst case’ atmospheric
greenhouse gas concentration trajectory (referred
to as a Representative Concentration Pathway or
RCP)—the RCP8.5 pathway. Based on these uplift factors, Table 1 summarises
how flood risk at each of the sites is predicted by
the modelling to change between the historical
period (1961–1990) and the two future time
horizons considered: the 2050s (2041–2060) and
the 2070s (2061–2080).
The following findings and recommendations (see
also Appendix 2) are presented for the three sites
considered:
BGS Keyworth
• The site is not at risk of flooding from rainfallrunoff causing the water level within the
channels running along the north-west and north-east of the site to rise and inundate parts
of the site.
• The critical storm duration (see Glossary for
definition) for BGS Keyworth was calculated to
be seven hours.
• There are three culverts in the channel along the
north-west of the site. If we adjust the historical
7-hour duration, 100-year return period summer
storm to account for climate change, then the
modelling indicates that the culverts in the
drainage channel along the north-west of the
site will surcharge but not result in inundation
of any parts of the site. (Summer and winter
storms are treated separately statistically by flood
hydrologists because summer storms are more
intense).
• Considering the same storm as described in
the previous bullet, then if it is assumed that the
bottom half of the culverts become blocked, the
modelling predicts that the Platt Lane entrance
to the site will be inundated by approximately
20 cm of water. No other part of the site would
be affected.
• Again, considering a 7-hour storm with a return
period of 100 years (calculated using data for
the period 1981–2020), analysis of the UKCP18
climate projections for RCP8.5 suggests that the
frequency of this event will change to:
» 1 in 20 years over the period 2021–2040
» 1 in 10 years over the period 2061–2080
• BGS facilities team should inspect the culverts
at least annually and arrange for any debris
to be cleared by the appropriate authority, if
necessary.
• BGS should make Nottinghamshire County
Council, the Lead Local Flood Authority (LLFA)
for Keyworth, aware of this work, given the
potential vulnerability to flooding of the new
homes recently built on the northern side of
Platt Lane, and of Severn Trent Water’s sewage
pumping station at the corner of Platt Lane and
Nicker Hill.
• There has not been sufficient information
about the site’s drainage network to assess
the risk of water appearing on the ground
surface when the drainage network becomes
surcharged. Furthermore, the development of
a model to do this would be a complex task.
Consequently, we have modelled the capacity
of the subsurface drainage pipes and used
this as a proxy to indicate which parts of the
system are more likely to cause water to pond
on the surface. Those pipe sections that have
been simulated to surcharge, or exceed 90% of
their capacity, during a 30-minute storm, need
further investigation. The model simulates that
6% of the network’s pipes exceed 90% of their
capacity during a 30-minute, 10-year return
period storm, which increases to 9% during a
30-minute, 75-year return period storm. First, the
slopes and lengths of the problematic network
sections should be measured accurately, and
the modelling exercise repeated to confirm the
findings of this study. Updating and rerunning
of the model would be relatively quick. After
confirming the fidelity of the model, several
potential solutions could then be reviewed, and
their costs and benefits evaluated against the
level of risk that NERC BGS are willing to accept.
Solutions could include replacing small diameter
pipes with larger pipes, increasing the slopes
of the pipes, optimising the size of catchment
areas generating runoff by altering the direction
of surface flow paths/directions. It is important
to maintain the drainage infrastructure to avoid
surcharging of the network and flooding.
BGS Edinburgh
• The levee and flood gates constructed along
the Murray Burn in 2020 have enhanced the
protection of the Lyell Centre. However, our
modelling predicts that the Lyell Centre would still be affected by flood water under a 20-year
return period storm. We conclude that the
levee is not sufficiently high at its downstream
end and, based on our new drone-based
LIDAR survey of land surface elevations,
flood water overtopping the levee here flows
towards the Lyell Centre. If it is considered
that the degree of flood protection is currently
insufficient, we recommend that NERC and
Heriot Watt University discuss what the options
are for increasing the level of protection to the
Lyell Centre. For example, this could include
extending the levee downstream and increasing
its height, or potentially increasing the crosssectional area of the channel.
• The critical storm duration for BGS Edinburgh
was calculated to be seven hours. Considering
a 7-hour storm with a return period of 100 years
(calculated using data for the period 1981-2020),
analysis of the UKCP18 climate projections for
RCP8.5 suggests that the frequency of this event
will change to:
» 1 in 20 years over the period 2021–2040
» 1 in 7.1 years over the period 2061–2080
• Our modelling has shown the potential for
flooding of other buildings on the Heriot Watt
campus, e.g. the Energy Academy and the
buildings north-east of the Lyell Centre on the
opposite side of the Murray Burn and Research
Avenue South. This report should be shared
with the Heriot-Watt estate management
department to make them aware of the risks to
the occupiers of these buildings, and to allow
them to consider any necessary actions.
NCAS Capel Dewi Atmospheric
Observatory (CDAO)
• The south-east corner of the site was flooded
on 21 January 2018. Measurements of rainfall
every 10 minutes during this day have been
made available by the CDAO’s Project Scientist.
Comparison against long-term historical
observations of rainfall has indicated that the
design storm that most closely matches the
peak rainfall intensity and total rainfall of the
observed storm has a 7-hour duration and 30-
year return period.
• Land surface elevation data for the site are
only available on a relatively coarse, 5 m grid.
Because of this, there is significant uncertainty
about the cross-sectional shape, and slope, of
the Afon Peithyll, which flows east to west along
the south of the site. The results of the modelling
must, therefore, be considered as ‘indicative’.
• For a 7-hour, 30-year return period design storm
the current model simulates flooding that was
more extensive than that observed in January
2018. However, it does indicate the area of the
facility that is at higher risk—the south-east
and east of the site, which is consistent with the
observations.
• Simulation of the influence of the culvert
(approximately 300 m downstream of the
site) and whether it is partially blocked or not,
suggests that it has little impact on the flood risk
of the site.
• The critical storm duration for the site was
calculated to be four hours. The modelling
suggests that a 4-hour storm with a return period
of seven years will initiate out of bank flooding at
the south-east corner of the site.
• Considering a 4-hour storm with a return period
of 100 years (calculated using data for the
period 1981–2020), analysis of the UKCP18
climate projections for RCP8.5 suggests that the
frequency of this event will change to:
» 1 in 20 years over the period 2021–2040
» 1 in 10 years over the period 2061–2080
• A survey of the Afon Peithyll and its floodplain is
needed to define the dimensions and slope of
the channel accurately and improve confidence
in the model.
• A number of engineering options are listed that
could be considered to protect the site from
flooding; their viability would depend on the
characteristics of the site, cost, and possible
environmental impacts.
• Consideration could be given to the feasibility,
and costs and benefits of moving infrastructure
located in the south-east of the site, where flood
risk is higher, to another part of the site
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