EXPLOITATION OF AQUIFERS

Itzel Almache Joseph Hernandez Carol Pacheco Alexandra Teran

Purpose of the research

Main calculations:Examining the basic parameters that have to be

determined and analyzed prior an aquifer exploitation

Ecuador Data:

Groundwater abstraction: 0.09% of total water consumption

Highly productive intergranular aquifers and fissure aquifers: Over 20%

Access to water sources is an increasing need :

• Population growth• Polluted superficial

water• Global warming:

• Pollution• Deforestation• CO2 emissions• Imbalance of

ecosystems

Blue: Lithological units permeable intergranular porosity Green: Lithological units permeable by crackingBrown: Lithological units virtually no exploitable groundwater

Feasibility of exploiting an aquifer

Hydrological cycle: INPUTS, OUTPUTS and THROUGHPUTS Water quality

Water quantity

POPULATION DEMAND ENVIRONMENT PROTECTION

AQUIFERWater bearing geological formation that can store and yield usable amounts of water and are identified by characteristics such as type, areal extent, depth form the land surface, thickness, yield, and direction of groundwater movement.

AQUIFER FORMATION

• Medium for the transmission of groundwater: Saturated formations below the surface

• Infiltration and movement• Returning to the surface

UNSATURATED ZONE (vadose zone)

SATURATED ZONE

From water table to ground surface

Water-filled pores that are assumed to be at hydrostatic pressure

TYPES OF AQUIFERSA: Unconfined aquifer: Water table function as its upper boundary B-C: Confined aquifer: Delimited from above and below by impermeable formations

Artesian Aquifer: Water occupies the total amount of pores or voids of the geological formation, a well in this type of aquifer will flow freely without pumping.

GROUNDWATER MOVEMENT

The direction and rate of movement are determined by the lithology stratigraphy and structure of geological deposits, represented by hydraulic properties

GROUNDWATER MOVEMENT

Porosity p=Vv/Vt Vv : Volume of the pores of a rock or soil sampleVt : Total volume of both pores and solid material

Permeability Ability of porous materials to allow fluids to move through it

Hydraulic conductivity

Rate of flow of a fluid through porous materialExpressed in meters per day

Hydraulic head (h)

Driving force that moves groundwater. It combines fluid pressure and gradient

h= Z+P/ ρg Z is the elevation head P is the fluid pressure at the point exerted by the column of water above the point.

GROUNDWATER MOVEMENT

Transmissivity (T)

Ability of an aquifer to transmit groundwaterT=Kb

K is the hydraulic conductivity (m/day), and b is saturated thickness of an aquifer (m).

Specific yield (Sy)

Amount of water that can be available for supply or consumption

𝑺𝒚 = g /Vt𝑽Vg is the volume if water drained by gravity, and Vt the total volume. For unconfined aquifers (Sy is between 0.05 and 0.3)

Darcy’s Law Q=-KA (dh/dl) Q is the volumetric flow rate, K is the Hydraulic conductivity, and A is the cross-sectional area of flow

AQUIFER STORAGEVolume of water released from storage with respect to water level and surface area of the aquifer Sum of the specific yield and the specific storage multiplied by the thickness of the aquifer

STORAGE OF UNCONFINED AQUIFERS• Water released Gravity drainage as the aquifer materials are dewatered during pumping

• Storage coefficient 0.01 to 0.30.

STORAGE OF CONFINED AQUIFERS• Water released Compression of the aquifer and expansion of the water when pumped.

• Storage coefficient • 1 x 10-5 to 1 x 10-3

WATER BALANCE

• Lateral subsurface inflow (QLS)

• Rainfall recharge (QRR)

• Recharge from nearby rivers (QRN)

• Recharge due to irrigation (QIR)

• Sewage return (QSR).

• Natural discharges such as springs (QSQ)

• Lateral subsurface outflow (QLA)

• Evaporation from groundwater table (QEGT)

• Groundwater usage through wells: such as domestic and industrial (QDI) water uses

• Irrigation water uses (QIW)

INPUTS

OUTPUTS

One of the most important analyses is water balance, which includes recovering the total inputs and outputs during a period of time, In the example a month of analysis

A well with a radius of 0.5 meters completely penetrates an unconfined aquifer gravel with a hydraulic conductivity K = 30 m/day and a height H = 50 meters. The well is pumped until the water level inside the object is 40 meters from the background. Assume that

the pump does not affect the pressure head greater and equal to 500 meters radius, and the loss in the well are negligible.

Determine which the pumping flow rate is.

EXAMPLECase: Unconfined Aquifer.

EXAMPLECase: Confined Aquifer.

A well fully penetrates a 25 m thick confined aquifer. After a long period of pumping at a constant rate of 0.05 𝑚3/𝑠 the drawdowns at distances of 50 and 150 m the well were observed to be 3 and 1.2 m, respectively. Determine the hydraulic conductivity and transmissivity.

Determine the hydraulic conductivity and transmissivity.

Figure 4. Hydraulic Conductivity (Heath, 1983)

CONCLUSION.

Aquifers have been and are one of the most important hydric resources to supply the society.

Permeability is analyzed for many different reasons such as: letting us know about the water flow inside the aquifer, and to get information about the exploitation flow.

Transmissibility depends on the permeability coefficient and the aquifer thickness, which let us know about the water flow.

The exploitation of aquifers has turned one of the most important topics in the world with a lot research work.

REFERENCES.

Bear, J. (2007). Hydraulics of Groundwater. New York , NY, USA: Courier Corporation .

Cech, T. V. (2009 ). Principles of Water Resources: History, Development, Management, and Policy. Hoboken , New Jersey, US: John Wiley & Sons.

Delleur, J. W. (2006). The Handbook of Groundwater Engineering, Second Edition (Second edition ed.). Boca Raton, Florida, US: CRC Press.

USACE, Genetti, Albert J., U.S. Army Corps of Engineers (1999) Engineering and Design: Groundwater Hydrology. EM 1110-2-1421

INAMHI. (2011). Introducción a la hidrogeología del Ecuador. Quito- Ecuador.

Kasenow, M. (2001). Applied Ground-water Hydrology and Well Hydraulics (Second Edition ed.). Highlands Ranch , Colorado, US: Water Resources Publication .