Unit 05 : Advanced Hydrogeology

Groundwater Resources

Groundwater as a Resource

• Large Regional Flow Systems

• Well Yield Analysis

• Artificial Recharge

• Conjunctive Use

• Aquifer Management

Overview

• Groundwater forms an integral part of the water cycle. • Increasing water demands in urban and rural areas put

increasing pressures on the use of groundwater. • Increasing contamination of the resource as a result of urban,

industrial and agricultural expansion, make it essential to properly manage these resources to guarantee their long term sustainability and to preserve water quality.

• Soil salinisation is often associated with irrigation practices but is also driven by natural groundwater processes.

• Integrated catchment management including groundwater is the key to solving the continuously expanding environmental problems of salinity, water logging and land degradation as well as the preservation of ecosystems.

Potential of Groundwater Resources• Groundwater resources in many countries are coming under

increasing threat from growing demands, wasteful use, and contamination.

• Surface water resources are particularly vulnerable to pollution, and are often limited in magnitude, particularly in arid regions.

• Groundwater resources are hidden and often poorly understood, but they are widespread, relatively easy to protect from contamination, and their development potential is great.

• Shallow groundwater in particular is relatively easy to access, and suitable for small scale development for domestic, livestock, and irrigation use in less developed countries.

Groundwater Replenishment

• The replenishment or recharge of shallow aquifers is of particular interest, as the annual recharge represents an upper limit of the quantity of water which can be abstracted without “mining” groundwater.

• In most situations, however, natural recharge to an aquifer emerges somewhere as natural discharge, sustaining stream flows and keeping wetlands wet.

• Therefore only a proportion of recharge can be abstracted for consumptive uses such as irrigation, in which used water is not returned to the aquifer.

Pumping Withdrawals

• Prior to exploitation by pumping, groundwater recharge is balanced by discharge to springs, streams, rivers and lakes.

• Withdrawal of water from wells is an additional stress that must be balanced by:

1. An increase in recharge

2. A reduction in discharge

3. A reduction in groundwater storage

• Groundwater, managed in a responsible and sustainable manner is a renewable resource.

Safe Yield

• Management of groundwater systems requires some kind of yield analysis to determine how much groundwater is available.

• The term “safe yield”, coined by Lee(1915), is used to denote the sustainable maximum rate at which water can be withdrawn without dangerous depletion of storage.

• Lee’s definition is conceptually sound but lacks any guidance on what might constitute “dangerous depletion”.

Conkling and Banks

• Conkling (1946) was more specific and much more controversial:

• “Safe yield”, defined by Conkling and modified by Banks(1953), is an annual extraction rate that does not:

1. Exceed the average annual recharge;2. Lower the water table so that pumping is

uneconomic;3. Lower gradients so as to admit intrusion of water

of undesirable quality;4. Fail to protect existing water rights.

Sustainable Yield• The Conkling-Banks single-valued concept of safe yield

encompasses:– Hydrologic considerations– Economic considerations– Quality considerations– Legal considerations

• Some argue that safe yield has no unique value and that modifications to recharge, discharge and storage in a system can modify the safe yield.

• Although this is true, it does not invalidate the four components of the Conkling-Banks definition.

• It is impossible to sustainably develop an aquifer if these components are disregarded, although their interpretation needs to be treated as flexible.

ULARA

• The Upper Los Angeles River Area (ULARA) is a useful example of the application of safe yield concepts.

• ULARA is bounded by mountain ranges and hills and forms an identifiable basin.

• Groundwater is extracted from a thick and productive valley-fill aquifer in an arid region with limited recharge (precipitation = 356 mm/y).

• As population grew and water demands increased, natural discharge to streams and rivers was eliminated and well-hydrographs demonstrated a 30-60 m decline in storage between 1930 and 1968.

Recovery• In 1968, groundwater withdrawals were limited by court

action to 350,000 m3/d• The rate prior to the court action was >500,000 m3/d• Hydrographs subsequently levelled out and recovered by

the mid 1990’s• The safe yield of the San Fernando Basin (the major basin

in ULARA) was estimated at just under 150,000 m3/d based on recharge from precipitation.

• Water is also imported into the basin to supplement recharge and this amounts to about 150,000 m3/d so the total recharge balances the total withdrawals (the withdrawals for the San Fernando Basin alone are about 300,000 m3/d)

ULARA Management

• ULARA supplies Los Angeles, Glendale and Burbank.• The ULARA management strategy allows each city a

water allocation based on “safe yield”.• The cities can “bank” any unused allocation and

withdraw it in subsequent years.• The ULARA management scheme is based on simple

water-balance or hydrologic budget calculations.• The latest management strategy uses a basin-wide

computer model to simulate regional aquifer response.

Groundwater Basin Management• GBM is defined as planned use of basin

yield, storage space, transmission capabilities and water in storage, including:

1. Protection of natural recharge and use of artificial recharge;

2. Planned variation in the amount and location of pumping over time;

3. Conjunctive use of groundwater and surface water sources;

4. Protection and maintenance of groundwater quality.

Management Tools

• Basin management requires a well-defined limit on the quantity of water that can be pumped which is largely based on the safe yield concept.

• Artificial recharge encompasses a range of engineered activities to supplement natural inflows, and

• Conjunctive use involves the combination of surface water and groundwater sources to meet a single demand.

Artificial Recharge

• Artificial recharge involves augmenting the natural infiltration of precipitation or surface water into the ground by some kind of engineered method.

• Artificial recharge is used to:1. Replenish depleted storage

2. Prevent or retard saline intrusion

3. Store water where surface storage is limited or unavailable

– Arid climates

– Urban areas

– Tidal rivers

Early Artificial Recharge I

• Early interest in artificial recharge focused on the use of drainage (recharge) wells to reclaim wetlands for agriculture. Many of the drainage wells failed due to clogging by sediment suspended in the drainage water.

• Drainage wells that recharged storm runoff and sewage to the Floridian aquifer, consisting of highly porous and permeable limestone, were more successful.

• Drainage wells tapping highly fractured basalt aquifers were also successful including use of a pit and wells to drain surface water into basalts in the Snake River Plain of Idaho.

Early Artificial Recharge II• Significant interest developed during the 1930s, in the use

of artificial recharge to conserve or enhance groundwater storage.

• In California, artificial recharge of alluvial aquifers with storm runoff by use of spreading basins was a widespread practice by the 1930s.

• In New York, water levels in a significant area of western Long Island had been drawn down below sea level by the early 1930’s due to groundwater pumping, much of it for air conditioning.

• Legislation passed in 1933 required that groundwater pumped for air conditioning be recharged, either by well injection or through spreading basins.

Artificial Recharge Systems

Water Spreading

• High permeability materials (sands and gravels) can give recharge rates from 0.5 to 15 m3/d/m2.

• Recharge rates reduce over time as the effective head gradient reduces.

• Water spreading involves diversion of surface water to topographic lows such as abandoned pits or detention ponds and reservoirs.

• River valley sands and gravels are utilized by releasing stored storm-water to infiltrate slowly through streambeds.

• Water traps are employed to increase infiltration in streambeds. The traps are earthen dams of variable height, usually 1 m to 3 m, that are constructed of locally available materials.

Recharge Lagoons and Trenches

• Unless particulates are controlled by sedimentation in a separate basin, clogging can become a serious problem.

• Cutwaters are excavations of variable dimensions, used as reservoirs, built in low-lying areas. Their primary objective is the harvesting and storage of surface waters.

• Recharge lagoons are custom-built impoundments in the recharge areas of aquifers.

• Wastewater recharge lagoons can be used instead of clean water and improvements in both bacterial and chemical quality are possible in the recharge process (Coliforms, BOD, COD, TOC, NH4

+ and NO3- ).

Recharge Wells

• Recharge wells tend to operate in the range 500 to 5,000 m3/d.

• Wells screens and gravel packs have to be carefully designed and water treated to remove particulates.

• Recharge wells using wastewaters require tertiary treatment to drinking water standards.

• Candidate wells for recharge are often production wells in depleted high-yield aquifers where high injection rates are possible at modest heads.

Compatibility of Source Water• Compatibility of source water for artificial recharge is

determined by comparing major-ion and trace-element concentrations in source water and receiving groundwater and evaluating the potential for any adverse chemical reactions.

• For example, the addition of source water with small concentrations of Ca2+ and HCO3

- to groundwater with large concentrations of these constituents may dilute the aquifer concentrations.

• Alternatively, the source water may cause more Ca2+ and HCO3

- to be dissolved from the aquifer material, which may lead to plugging of the aquifer material by precipitation as the water flows down-gradient, thereby limiting the recharge capacity.

AR: California and Texas• In the late 1960s, the California Water Plan was approved to import

several billion cubic metres of water from northern to southern California each year, and that much of the imported water be stored in the subsurface through artificial recharge.

• A proposal to import water from the Mississippi River to the Southern High Plains of Texas, resulted in interest in artificial recharge in the Southern High Plains of Texas and New Mexico.

• The project emphasis changed to consider recharge of sediment-laden playa lake water. Several artificial-recharge experiments were conducted in the 1970s.

• Artificial recharge of the Evangeline aquifer in the Houston area as a means to alleviate subsidence was investigated in the late 70s.

• Recharge of the Hueco Bolson, the water supply for the City of El Paso, was investigated by a pilot artificial recharge project and ensuing recharge operations after 1980.

AR: New York• In New York, plans to convert many areas developed with wells

and septic systems to municipal water supply and sewage treatment resulted in a strong interest in artificial recharge of tertiary treated waste water.

• Artificial recharge of storm runoff by use of spreading basins has been practiced on Long Island since the 1930s. More recent studies have been conducted to determine whether existing spreading basins for storm water recharge could serve the dual purpose of recharging treated sewage effluent.

• A spreading basin at the site of a water treatment plant in central Long Island was used for additional recharge experiments.

• Interest in artificial recharge in the New York City area continues to the present day.

AR: Florida• In Florida, interest continues into the hydrologic and water-

chemistry impacts of drainage wells in the Orlando area. Recharge of the surficial aquifer with tertiary treated effluent using spreading basins also takes place in Orlando.

• Interest has developed in the use of connector wells to recharge the deeper Floridian aquifer from the surficial alluvial aquifer.

• Recharge of the Floridian aquifer with surface water also received study. The feasibility of using canal water to supplement the groundwater supply has been investigated.

• Storage of fresh surface water in a brackish limestone aquifer has also received interest. Results suggest that clogging due to the dispersion of sodic clays in the aquifer that can be stabilized by chemical pretreatment.

• Interest in artificial recharge in Florida continues with the use of aquifer storage and pumping as an aid to recovery of the Everglades wetlands.

AR: High Plains Aquifers• Increased development of groundwater for irrigation

throughout the High Plains led to artificial recharge studies in the states Kansas, Nebraska, Colorado, South Dakota, and North Dakota.

• This led to the recently completed High Plains Groundwater Demonstration Program, involving artificial-recharge.

• Other studies associated with artificial recharge in the High Plains states include feasibility and modeling studies of artificial recharge of alluvial aquifers Colorado and South Dakota.

• Interest in artificial recharge in the High Plains continues.

AR:The Future• The use of artificial recharge to store surplus surface water

underground can be expected to increase as growing populations demand more water, and as the number of good dam sites still available for construction becomes fewer.

• Artificial recharge may be used to store treated sewage effluent and excess stormwater runoff for later use.

• Groundwater recharge may also be used to mitigate or control saltwater intrusion into coastal aquifers.

• In order to accomplish these uses without deleterious environmental consequences, the optimum combination of treatment methodologies before recharge and after recovery from the aquifer must be identified.

• It will also be necessary to consider the sustainability of soil-aquifer treatment and health effects of water reuse when using treated wastewater as the recharge medium.

Future Considerations

• Because of the increasing need for underground storage of water, more artificial recharge systems will have to be constructed on finer textured soils like sandy loams to light loams, as coarse sands and gravelly materials will not always be available.

• Field and laboratory studies need to be carried out to predict sustainable infiltration rates for such soils and to develop design and management criteria to minimize infiltration reductions due to soil clogging.

Conjunctive Use• Conjunctive Use -

Integrated management of surface water and groundwater

• There are two basic scenarios:– Combined use of independent

resources– Interconnected stream-aquifer

systems

• Interconnected systems are more complex to manage

Demand

Stream Hydrograph

Groundwater

SurfaceWater

Surface-Groundwater Interactions

• When surface water and groundwater sources are in the same basin, there is interaction since the two are coupled through the baseflow component of streamflow.

• The amount of groundwater that has to be supplied is increased due to these interactions.

• If the loss of baseflow is distributed in time, there is a net gain.

Stream Hydrograph

SurfaceWater

Modified Hydrograph

Stream Hydrograph

SurfaceWater

Modified Hydrograph

River Regulation

• A regulated river is a river or stream where the flow has been controlled or modified from its natural conditions.

• The most typical modification is that imposed by a major dam.

• Groundwater can also be used both directly and indirectly to regulate river flows.

• In general, constant flows occur more frequently in regulated rivers used for irrigation or water supply.

• Unfortunately the native fauna in our rivers are adapted to natural fluctuations in flow conditions.

River Ecology

• Rivers regulated for irrigation deliver water in seasons of low rainfall and this creates a high flow which is out of phase with the natural regime.

• This can alter the natural cues needed for native fish to migrate and spawn.

• It can create an environment more suited to alien, as opposed to native, species.

• In some cases there is not enough water available for wetland filling or flooding resulting in a gradual decline in wetland health.

• In regulated rivers water is captured in winter, stored, then released over the summer.

• This can reverse the natural flow pattern to which native species have adapted.

River Transmission Issues• River regulation can result in unnaturally constant flow in summer

as water is transmitted for or water supply, sometimes hundreds of kilometres.

• This constant flow has ecological impacts such as drowning of riparian (river bank) vegetation and wetlands which are adapted to seasonal inundation.

• Constant flow also prevents natural drying of water bodies such as wetlands.

• Drying is an important part of the life cycle of many native species and can help to eliminate alien species that are not adapted to these conditions.

• Sudden rises and falls in river levels resulting from water release and subsequent extraction can have an effect on bank stability causing slumping, loss of riparian vegetation, erosion and sedimentation.

Environmental Flows• Environmental flows are produced by releasing water to simulate,

maintain or repair natural flow patterns.• Although it is impossible to restore flows to pre-regulation

conditions, the aim of environmental flow management is to mimic natural flow regimes, providing cues for key life cycle events such as spawning and migration.

• Flow management can also rehabilitate and improve ecosystems.• The concept of an environmental flow includes managing for:

– water level rise and fall– duration of a flow event– velocity of water in the channel– seasonality of flows– need for flood pulses or high flows– protection of water levels during periods of low or no flow.

Regulation with Groundwater• The River Severn is the longest river in Great Britain and

is one of the most important environmental features of the region providing a diverse range of habitats for wildlife.

• It is a major water resource river supporting abstractions for public water supply and to a lesser extent for industry and agriculture. The Severn is also valued for its navigational and recreational uses.

• During periods of dry weather the river is regulated by reservoir releases, principally from Llyn Clywedog, to maintain flows at an acceptable level.

• In very dry years additional releases to the river can be made from the Shropshire Groundwater Scheme.

Lyn Clywedog

• The dam across the River Clywedog near Bryntail is one of Britain’s tallest concrete buttress dams.

• Llyn Clywedog, built in 1963, holds water to be used for River Severn Regulation. Its location was chosen to take advantage of high rainfall in the Welsh hills. This rainfall is stored and released from the reservoir in times of high demand, particularly during dry periods.

Shropshire Groundwater

• The Shropshire Groundwater Scheme is designed to be used, on average, once every three years to meet peak dry weather demands for water.

• Water is pumped from groundwater reserves naturally stored within the Triassic sandstone underlying much of North Shropshire.

• This water is pumped out and released to the River Severn to enhance flows in the river.

• The River Severn is regulated with surface water from both the Llyn Clywedog reservoir and groundwater from the Triassic Sandstone Bedrock Aquifer.

Combined Use of Groundwater• Stocks Reservoir is used to supply the Fylde District of

Lancashire with drinking water via the Hodder aqueduct.

• Water can be transferred from the River Lune to the River Wyre via a tunnel.

• The surface supplies are inadequate in drought years.• A large groundwater pumping capacity is available in

the Fylde Aquifer (Permo-Triassic Sandstone) to augment the surface sources.

• Water is supplied directly from rivers, reservoirs and wells via a single treatment plant.

Lancashire Combined Use Scheme

Lancashire Hydrograph

AR and Conjunctive Use• The River Thames is a tidal river in southern England

with high baseflow from the the Chalk Regional Bedrock Aquifer.

• Some tributaries are almost 100% groundwater supported streams (such as the River Pang).

• Water quality is good and most of the water is extracted at the tidal limit (Teddington weir) and treated for supply.

• The Chalk Aquifer around London was heavily depleted and provides a high storage volume for artificial recharge.

Thames Valley Groundwater

River Pang Hydrograph

Lee Valley Artificial Recharge• In winter

– Surplus water from tidal limit of River Thames

– Stored in surface reservoirs– Treated and recharged into

former Chalk aquifer production wells

• In summer– Water recovered from wells– Temporarily stored in surface

reservoirs or pumped for direct supply

Lee Valley Winter

Lee Valley Summer

Yaqui Basin, Mexico• The Yaqui Basin of Sonora, Mexico has rapidly grown

from very small-scale subsistence farming to over 225,000 cultivated hectares, irrigated heavily through several reservoirs and a distribution network of canals.

• Groundwater pumping from the coastal aquifer has also increased, and without a management model in place, these irrigation wells often run dry or become excessively saline.

• The water-bearing formation is entirely in interbedded sands and gravels derived from the Sierra Madres and overlying deeper bedrock units in thicknesses ranging from 80-240m and occasionally exceeding 400m.

Yaqui Wells

• Deep wells discharge to the irrigation canal system.

• Approximately 150 agricultural groundwater supply wells are managed conjunctively with surface supplies in the Yaqui.

• The wells are operated to maintain both quantity and quality demands.

Water Resource Planning Models

• Integrated hydrological models have been used for several decades for examining the hydrological and economic impacts of water policy options.

Yaqui Water Resource Planning

• A semi-arid climatic regime, an intensely irrigated agricultural environment, and a growing urban centre provide challenges to water resource planning and management.

• The use of integrated hydrological models in water policy evaluation, the Yaqui provides an ideal setting for examining the hydrological and economic impacts of water policy options. The system has multiple strongly interacting components and models help planners to understand and predict the interactions.

California Water Management• The goal of the Conjunctive Water Management Program is

to increase water supply reliability through the planned, coordinated use of surface water and groundwater resources.

• Emphasis is on:– Establishing local basin-wide planning partnerships, – Facilitating local basin monitoring, – Implementation of locally controlled and managed projects, – Maintaining priority for in-basin water needs when facilitating out-of-

basin transfers, and – Sharing technical data for planning and developing conjunctive water

management projects.

• A reliable water supply is central to sustaining California's present and future economic, social and environmental viability.