Water Resources

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1-in-100year flood

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aflood that has a 1% chance of occurring in any given year

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100year storm

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arainfall event that statistically has a 1% chance of occurring in any givenyear

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Actual evapotranspiration

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the actual quantity of water removed from a surfacedue to evapotranspiration

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Anisotropic Aquifer

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dueto layering of sediments, hydraulic conductivity is not equal in all directions

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Aquiclude

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is incapable of transmitting significant quantities of water on a regional scale (clays, shales)

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Aquifer

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abody of water stored within rock that stores and transmits important quantities of groundwater(found usually in sands and gravels)

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Aquitard

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is a saturated body of rock that impedes water flow (doesn’t stop italtogether) (found usually in silts and sandy clays)

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Baseflow

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theportion of streamflow that comes from groundwater

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Catchment

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thearea drained by a river system

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Capillary Fringe

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The capillary fringe is the subsurface layer in which groundwater seeps up from a water table by capillary action to fill pores. Pores at the base of the capillary fringe are filled with water due to tension saturation.

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ChannelFlow

DiffuseFlow

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concentrated flow

unconcentrated flow

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Effectiveporosity

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Theinterconnected pore volume or void space in a rock thatcontributes to fluid flow or permeability in a reservoir.Effective porosity excludes isolated pores and pore volume occupied bywater adsorbed on clay minerals or other grains.

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Eutrophication

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excessive richness of nutrients in a lake or other body of water, frequently due to run-off from the land, which causes a dense growth of plant life.

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Evapotranspiration

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evaporation from wet leaves, soil, surface water and plants,this is influenced by moisture and soil texture alongside vegetation age andtype

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Flow Regime (river)

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variation through the year, tends to be based on source of flow and distribution throughout the year.

Original complex – more than one high or low flowseason and possibly different sources of streamflow dominating at times

Changing complex – different parts of the catchmentexposed to different climates

Simple– one high flow, one low flow and one dominant source of water

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Hydraulicconductivity

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the ease with which water can make it through pore spaces andfractures

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Impermeable

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waterpasses with difficulty

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Infiltration capacity

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the maximum rate at which water can soak into the soil

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Infiltration rate

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the rate of supply of water to the soil – velocity ofwater absorbed

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Lysimeter

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an apparatus for measuring changes due to moisture loss,percolation, etc. undergone by a body of soil under controlled conditions.

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NaturalEutrophication

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occurs as a slow process and happens when production andconsumption do not cancel each other out and the lake becomes over fertilised

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Organicpollution

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excess of organic matter is released into the water. Highlevels of organic material in the water causes the number of decomposersincrease. This increased decomposition uses high amounts of oxygen, depletingoxygen from the water body. Death of aquatic creatures requires moredecomposition which further removes more oxygen from the water body.

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Overland flow

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the flow of water over the Earth’s surface

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Permeable

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easyto pass through

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PhreaticZone

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Zone above the water table that is fully saturated

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Porosity

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(voidvolume/total volume ratio)

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Potentialevapotranspiration

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theamount of evapotranspiration that would occur if there is no controlover water supply (there is a sufficient water supply)

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Primaryporosity

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theporosity formed by the original sedimentation process of the rock

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Rechargebody

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hydrologicalprocess where water moves downwards from surface water to groundwater as it isrecharged by rain, does not equal all rainfall due to interception, evapotranspirationand some rainfall may fall straight into the river

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RiverFragmentation

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theinterruption of a rivers natural flow by dams, inter-basin barriers or waterwithdrawal. In a recent study of 227 rivers assessed 37% were strongly affectedby fragmentation

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Runoff

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flowof water over the Earth’s surface

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Secondaryporosity

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a subsequent or separate porosity system in a rock such asfractures

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Specific Retention

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Sr – the water retained in the unsaturated zone after drainage under gravity

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Specific Yield

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Sy– amount of water which drains freely from a unit volume of saturatedrock for one unit drop in water table - % or fraction of the total volume ofinitially saturated rock

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Stormflow

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the river discharge generated by a storm

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Throughflow

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isthe lateral unsaturated flow of water in the soil zone or underlying porousrock, this returns to the surface as return flow in a stream or groundwater

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Macroporeflow

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throughsmall cracks or root channels

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MatrixFlow

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watermoving through small soil pores

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Pipeflow

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throughlarger cavities in the soil

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Total Porosity

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The total porosity is the total void space and as such includes isolated pores and the space occupied by clay-bound water.

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Transmissivity

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therate of flow under a unit hydraulic gradient through a unit width of aquiferthickness

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UnitHydrograph

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isdefined as the hydrograph resulting from an effective rainfall of 1mm evenlydistributed over the basin

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VadoseZone

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Zoneabove the water table which is partially saturated

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WaterBalance

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P =Q + E + ΔS. Precipitation (P), Runoff/Discharge (Q), Evapotranspiration (E),Change in storage/Groundwater/Infiltration (ΔS). Inputs are unlikely to equaloutputs locally. Take vegetation etc. into consideration in water balances.

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Watershed

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anarea or ridge of land that separates waters flowing to different rivers,basins, or seas.

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Velocity-areamethod

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estimationof water velocity (using an impeller meter) is multiplied by area of water in across section

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Acousticgauging

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Ultrasonic discharge gauges – record time for a beam ofacoustic pulses to cross a river at different depths (water level sensor isrequired and cannot be used where there is dense vegetation/high sediment load)

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RatingCurve

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o Measuresriver discharge at different water levels

o When plotted, the equation of the line of best fitallows discharge of any water level to be inferred.

o Care is necessary because:The curve can change shape when rivers burst banks;and there are inevitable errors with measuring discharge.

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Dilution gauging

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o Adds aknown concentration of a chemical into the river to measure dilution

o Concentrationv time graph is plotted

o Dilution gauging main disadvantage – difficulty inobtaining complete mixing of the tracer without loss of tracer and the problemof obtaining permission in some countries to inject tracer into water body,variations in water can make the measurement incorrectz

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Reasons for not exploiting groundwater:

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- Contamination – expensive to remediate

- Noteconomically viable

- Lowporosity rock meaning there will be a lackof stored water

- Lowpermeability/interconnectivity meaningwater passes with difficulty

- Lowreplenishment rate, if abstraction exceedsreplenishment there will be a lack of water and the aquifer can no longer beused

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Confined Aquifer

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this is an aquifer that is bounded above andbelow by confining, impermeable, bed

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Unconfined

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also known as a water table aquifer has aconfining layer below and the water table above

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effective porosity IS

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Specific yield + Specific retention

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Primaryporosity

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the proportion of a given volume of rockaccompanied by pores

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Effectiveporosity

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the porosity of rock which is interconnectedand contributes to fluid flow through the rock

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Capillaryfringe

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the layer of rock immediately above the watertable in which water is held by the capillary

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Anisotropy

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variations of properties with direction(directionally dependent)

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Principal Aquifers

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- Chalk– Cretaceous

- Jurassiclimestones

- Permo-Triassicsandstones

- LowerGreensands

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Environment Agency – HydrometricStations

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- River level

- River flow

- Rainfall

- Groundwaterlevel

- Alsomeasure climate but this is less important

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Hydrochemical Facies

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A distinct zone of groundwater than can be described as having achemical composition within defined limits. Best shown by a piper diagram.

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Source Protection Zones

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used to identify areas close to drinking watersources where the risk associated with groundwater contamination is greatest.Should be teardrop shaped and is separated into zones of risk.

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Well of Depression

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When the rate of inflow from the aquifer is exceeded by the rate ofpumping, drawdown will occur in a cone shape around the well because of radialflow. Lakes isolated will suffer and can be affected by a reduction of thewater table.

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Cultural Eutrophication

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Where humans artificiallyenrich lakes with nutrients. This occurs from fertilisers, sewage effluent, andnitrogen from exhausts.Onlysome lakes suffer from it – agricultural areas are likely to suffer as theremay be high levels of fertiliser and pesticides. If lake is at bottom ofcatchment there will be high run off so risk of eutrophication is higher

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How to measure age of groundwater

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Age can be measured by rate ofdecay of radioactive elements present in the water at low concentrations.

Importance: is the water amixture of different ages?

- Is itsuitable for being ‘mined’/abstracted- Was thewater recharged under different climatic conditions i.e. ice age

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SourceIsolation

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Source isolation – limitingthe flow of water through the contamination source region, using engineeredbarriers with low hydraulic conductivity

4 ways for this:

- Syntheticmembranes

- Slurrywalls

- Sheetpilings

- Grout

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Hewlett Hypothesis

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Infiltration capacity is now zerogiving saturation excess overland flow

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HortonianFlow

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When precipitation exceedsinfiltration capacity causing infiltration excess overland flow

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Potentiometric surface

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The potentiometric surface is the level towhich water rises in a well. In a confined aquifer this surface isabove the top of the aquifer unit; whereas, in an unconfined aquifer, it is thesame as the water table.

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Oligotrophiclakes

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“poorly – fed”. They lack nutrients and low productivity, maybe clear

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Eutrophic Lake

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"well– fed” – have high productivity and may well be murky owing to suspendedplankton

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Dimictic

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two overturns a year – typical of temperate climates

PIKE LAKE - Minnesota

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Monomictic

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one overturn a year – Mediterranean

Lake Titicaca - peru/bolivia

Lake Michigan

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Holomictic

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most lakes turn over at least once

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Meromictic

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never completely overturn (fed by dense salinewater)

Big Soda Lake - Nevada

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Oligomictic

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no set overturns a year as it is dependable on anumber of less predictable factors

Zaca Lake - Santa Barbara California

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Sources of water to stop a well from running dry

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- Water fromlong term storage

- Decrease innatural discharge from an aquifer

- Increase inrecharge man

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Typesof spring

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Depression spring – where ground surface intersects water table

Contact spring – contact between permeable and less permeable, intersects the water table

Artesian spring – Release of water from a confined aquifer

Tubular spring – coming from rounded solution channels

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Basic Remediation Methods

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Pump and treat – pump out contaminated groundwater and use water treatment to clean up

Source Isolation – limit the flow of water through the source region using engineered barriers with low hydraulic conductivity

Permeable reactive barriers – excavate some of the aquifer (trench) then replacewith a material to react with the contaminant i.e. iron filings

Monitored natural attenuation – a variety of physical, chemical or biologicalprocesses that act without human intervention to reduce mass toxicity, mobility volume or concentration of contaminants in soil or groundwater