Lecture #13 Ground Water

Size: px

Start display at page:

Download "Lecture #13 Ground Water"

Constance Daniel
5 years ago
Views:

1 Water in the ground is not found in vast underground lakes and rivers it is found in micropores around individual sedimentary grains. Lecture #13 Ground Water In Hawaii, ground water is found in the pores of lava flows the best being Aa flows. Porosity in sediments A. 30% porosity in well-sorted sediment B. 15% porosity in poorly sorted sediment C. low porosity in well-sorted, cemented sediment 1

2 Porosity percentage of empty space Permeability rate at which groundwater flows through crust Shale many small clay/silt particles high porosity, low permeability Sandstone sand grains medium to high porosity, high permeability if not cemented Individual Aa flows have porous clinker zones that offer the best aquifer characteristics Core zone Clinker zone Basalt Pahoehoe (low porosity and low permeability Aa (high porosity and high permeability in clinker zones not core zone) Intrusive Dikes (low porosity and low permeability) Oahu s coastal plains are fossil reef with this sort of porosity Hawaii aquicludes tend to be intrusive dike rock 2

3 Aquifer Aquiclude Artesian Well Important concepts in Hawaii Why? 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. Hawaii s orographic effect Cone of depression important local impact that controls hydraulic flow Can attract contaminants unintentionally can also be used to withdraw contaminates 3

Hawaii s freshwater (90% for drinking comes from ground water) sits on salt water Must

Aquifer are showing salt water intrusion The Waiahole Water Ditch was constructed in

(wet) side of the island to the Oahu Sugar Company plantations on the Leeward (dry)

to influent due to Lowering of groundwater For human use This system virtually

As a result, the marine life population was depleted and most importantly many taro

Decision Divides flow in half Windward gets almost 5 times more than historical But

moving p to the Philippines pp ((where labor is cheaper).

would be giving up a vast portion of water.

to it that the Waiahole water that had been taken from them eighty years earlier would

The commission's final order divides the 27 million gallons a day of water in the

4 Hawaii s freshwater (90% for drinking comes from ground water) sits on salt water Must be careful to avoid overpumping Iao Aquifer (Maui) and several wells in Pearl Harbor Aquifer are showing salt water intrusion 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 Many windward streams in Hawaii have gone dry from Effluent to influent due to Lowering of groundwater For human use 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. Decision Divides flow in half Windward gets almost 5 times more than historical But may be reduced in future In 1994 the Oahu Sugar Company announced that it would be moving p to the Philippines pp ((where labor is cheaper). p ) This it's entire operation meant that one of the biggest users of water on Oahu, would be giving up a 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 banded together to see to it that the Waiahole water that had been taken from them 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. 4

5 Hawaii s orographic effect 5

6 A freshwater lens system underlies much of southern Oahu Well A produces saltwater A 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) produce large volumes of freshwater by skimming water from near the top of the freshwater lens Shaft 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 min amounts of water. 6

Molokai water wars 15 in/yr 157 in/yr West Molokai Ranch has historically been owned by absentee companies who have tried several different ways of generating a profit from the land.

7 Molokai water wars 15 in/yr 157 in/yr 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 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 7

Movement and Storage of Groundwater The Hydrosphere

Movement and Storage of Groundwater The Hydrosphere The water on and in Earth s crust makes up the hydrosphere. About 97 percent of the hydrosphere is contained in the oceans. The water contained by landmasses