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Lecture #13Ground Water

Water in the groundis not found in vast undergroundlakes and rivers…it is found in micropores around individualindividual sedimentary grains.

In Hawaii, ground water isfound in the pores oflava flows…the bestbeing Aa flows.

Porosity in sedimentsPorosity in sedimentsA. 30% porosity in well-sorted

sediment

B. 15% porosity in poorly sorted sediment

C. low porosity in well-sorted,cemented sediment

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Porosity – percentage of empty space

Permeability – rate at which groundwater flows through crust

Shale – many small clay/silt particleshigh porosity, low permeability

Sandstone – sand grainsmedium to high porosity, high permeability if not cemented

Basalt – Pahoehoe (low porosity and low permeabilityAa (high porosity and high permeability in “clinker” zones

Clinker zone

permeability in clinker zonesnot core zone)Intrusive Dikes (low porosity and low permeability)

Core zone

Individual Aa flowshave porous“clinker” zonesthat offer the bestthat offer the bestaquifer characteristics

Oahu’s coastal plains are fossil reef – with this sort of porosity

Hawaii aquicludes tend to be intrusive “dike rock”

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Water in ground flows in response to hydraulic pressure…not gravity.Can flow uphill if hydraulic pressure demands it…not always related to surface topography.

Aquifer – Aquiclude – Artesian Well

Important concepts in Hawaii…Why?

Hawaii’s orographic effect Cone of depression – important local impact that controls hydraulic flowCan attract contaminants unintentionally…can also be used to withdraw contaminates

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Hawaii’s freshwater (90% for drinking comes from ground water) sits on salt waterMust be careful to avoid overpumping…Iao Aquifer (Maui) and several wells inPearl Harbor Aquifer are showing salt water intrusion

Many windward streams in Hawaii have gone dry fromEffluent to influent due toLowering of groundwaterFor human use

The Waiahole Water Ditch was constructed in the early 1900’s by sugar interests on Oahu in order to bring water from the Windward (wet) side of the island to the Oahu Sugar Company plantations on the Leeward (dry) side.

Waiahole Water Wars This system virtually eliminated the stream water from many areas of the windward side. As a result, the marine life population was depleted and most importantly many taro (Hawaiian staple food) farmers were unable to continue growing.

In 1994 the Oahu Sugar Company announced that it would be moving it's entire operation to the Philippines (where labor is cheaper). This

Decision – Divides flow in halfWindward gets almost5 times more than historicalBut may be reduced in future

p pp ( p )meant that one of the biggest users of water on Oahu, would be giving upa vast portion of water. Since the state had no clearly defined plan to handle such circumstances, numerous groups began to vie for the water. Many native groups and other interests from the windward side bandedtogether to see to it that the Waiahole water that had been taken fromthem eighty years earlier would be returned.

The commission's final order divides the 27 million gallons a day of water in the Waiahole system as follows: 14 mgd is to go to the leeward side; 6 mgd is to be restored to windward streams; and 7 mgd is to remain, for the time being, in windward streams. Of that last 7 mgd, 1.6 mgd is proposed to be placed in an agricultural reserve, while 5.4 mgd is categorized as "non-permitted" for now, but subject to future allocation by the commission.

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Hawaii’s orographic effect

http://soest.hawaii.edu/coasts/cgg_main.html

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A freshwater lens system underlies much of southern Oahu Well A produces saltwaterA freshwater-lens system underlies much of southern Oahu. Well A produces saltwater below the transition zone, well B produces brackish water from the transition zone, and well C produces freshwater. Horizontal shaft D (sometimes called a Maui shaft) producelarge volumes of freshwater by skimming water from near the top of the freshwater lensShaft E (sometimes called a Lanai shaft) is dug horizontally into one or more of the dike-bounded compartments. Location F indicates a perched water body containing minamounts of water.

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157 in/yr15 in/yr

Molokai water wars

West Molokai Ranch has historically been owned by absentee companies who have tried several different ways of generating a profit from the land.

•Profit goes offshore•Profit goes offshore•Portion of local population does not want tourism•Portion does want tourism•Highest per capita welfare/unemployment and subsistence living off land

West Molokai Ranch attempts to bring water onto their arid land have been met with lawsuits and vandalism