Coastal Aquifers definition, concepts and issues Coastal Aquifer Management in the Caribbean Lucila Candela Technical University of Catalonia-UPC 1

Hydrologic cycle Oceans & seas1370 (Mkm3)94 (%) yr Lakes & dams yr Wetlands<0, yr Rivers<0, w Water content0,07<0,012 w-1 yr Groundwater6042 w yr Glaciers yr Atmosferic water 0,01<0, d Biosferic waater <0, w 2

Hydrologic cycle. Close-up 3

Groundwater Hydrology- Hydrogeology 4 GME

Aquifer Water bearing geologic formation (comsolidated-unconsolidated) form which groundwater can be extracted Aquitard, aquiclude (impervious: clays, shale, granite…) 5 GME

Water bearing formations: types 6

Aquifers classification: hydrostatic pressure Unconfined aquifer (water table aquifer): water at atmospheric pressure confined aquifer : water at pressure > atmospheric Pressure (piezometric level). Confined beteen two aquitards 7 GME

ACUIFERO A ACUIFERO B ACUIFERO C C. Molano 8

ACUIFERO A ACUIFERO B ACUIFERO C Q1Q1 9

ACUIFERO A ACUIFERO B ACUIFERO C Q1Q1 Q4Q4 Q3Q3 Q2Q2 Q5Q5 10

ACUIFERO A ACUIFERO B ACUIFERO C Q1Q1 Q4Q4 Q3Q3 Q2Q2 Q5Q5 QrQr 11

ACUIFERO A ACUIFERO B ACUIFERO C Q1Q1 Q4Q4 Q3Q3 Q2Q2 Q5Q5 QrQr 12

Aquifer parameters : properties affecting water storage and groundwater flow (porosity, hydraulic conductivity) 13 Porosity  : defines the storage capacity of an aquifer (obtained in lab. Thorugh samples; in situ (kinematic): field tests, tracers, balance….

Groundwater movement: gw in ist natural state is Invariaby moving. The flow of aquifers is expressed by Darcy’s law 14 q = Q/A = -K grad h K: hydraulic conductivity Hydraulic conductivity, k: measure of an aquifer ‘s ability to transmit water (horizontal) Datum plane

Hydraulic conductivity, k: Geologic materials(horizontal) 15 Hydraulic Conductivity (m/d) ClassificationImperviousVery lowLowPermeable High permeability AquiferAquicludeAquitardPoor aquiferGood aquiferexcellent material Compact claySandly siltCoarse sand Sandy gravel ShalesiltSilty sandThick gravel GraniteSilty clayKartsThick sand

Groundwater flow : the rate of groundwater movement is governed by the hydraulic conductivity and and hydraulic gradient Steady-state: magnitude and direction of flow velocity any point in a flow field is constant in time Transient: just the oppposite Direction and rate: water table contour maps, piezometric (potentiometric maps) 16

17 Piezometric maps

18 Streamflow and groundwater levels groundwater fluctuations : evapotranspiration effects, rainfall, atmospheric pressure, tides, urbanization, man-made actions USGS

19 GW quality & Gw pollution Quality defined according to use: agriuclture, water Supply (standards) GW pollution: Changes in the quality of water as a result of man’s activity (different sources. Point and non-point Contaminants: chemicals, biological and radioactives Heavy metals (Fe, Cd, Ni, Mn..) trace non-metals (Cl, As, Se, No3 Organic susbstances: pesticides, petrol derivatives, emerging cont. Microorganisms: virus, bacteria Gw originates by rainfall which infiltrates thorugh soil. As it moves along flowlines its chemistry is altered by a variety of geochemical processes

20 Flow lines

21 Monitoring: quantity and quality Surveillance system of continuing measurements, observation and evaluation if necessary (scientifically based) in the area or basin of interest. - groundwater levels -sampling and analysis of gw quality -seawater intrusion, etc. Procedure involves a series of action steps and also changes along time Based in a good knowledge of the studied aquifer!!!!!!!!!!!!

22 Data representativity!!!! Nested piezometers Sampling for quality: -aquifer sampled -sampling devices -sample storage and transport -analytical procedure -hydrochemistry study of data (depending of the studied problem)

Coastal Aquifers Increasing population incresing water demand Gw supply overexploitation during droughts Seawater intrusion

Coastal Aquifers Prevention of salinisation is critical. Once an aquifer has been salinised, remediation is difficult. Detailed characterisation of coastal aquifers is essential for prevention and remediation. Given the large scale of seawater intrusion problems, this is a more formidable challenge than for conventional aquifers. IGME

Coastal Aquifers: islands USGS Seawater enters easily, but it is hard to push back

Coastal Aquifer Management in the Caribbean-II Effects of storm (seawater) surges Saltwater above freswater

Coastal Aquifer Management in the Caribbean-II Vithanage, 2008