The early Polynesians brought sugar cane with them and demonstrated that it could be grown successfully in the islands. The first commercially-viable sugar plantation, Ladd and Co, was started at Kōloa on Kauai in 1835. Others followed, including on Maui.
Sugar became part of the Maui landscape. More than 30-plantations of various sizes popped up on Maui. Over time, consolidations and closures gradually reduced the number to fewer, but larger, plantations. (Sugar Museum)
Sugar is a thirsty crop; in order to irrigate, in 1876 the initial Hāmākua Ditch was built, bringing water from streams from the windward and wet East Maui. A total of ten ditches were constructed between 1879 and 1923; this system makes up what is known today as East Maui Irrigation (EMI.)
Under natural conditions, most surface water would flow to the ocean; instead, this water has been diverted and artificially applied to the plant-soil system, creating a net increase in ground-water recharge. Irrigation-enhanced recharge greatly affects the groundwater system in central Maui.
Ground water is one of Hawai‘i’s most important natural resources. It is used for drinking water, irrigation, and domestic, commercial, and industrial needs. Ground water provides about 99% of Hawai‘i’s domestic water and about 50% of all freshwater used in the State.
The amount of recharge available to enter the aquifers is the volume of rainfall, fog drip, and irrigation water that is not lost to runoff or evapotranspiration or stored in the soil. (USGS)
The period 1926–79 had the highest estimated recharge; irrigation rates during this period were at least 50% higher than in any other period considered.
Prior to the early-1970s, about 190-million gallons per day (Mgal/d) of water diverted by East Maui ditches and 170-Mgal/d of groundwater withdrawn from shafts and wells was used to irrigate sugarcane fields in central Maui.
Groundwater recharge concerns have gone from bad to worse. Overall irrigation rates have been steadily decreasing since the 1970s, when large-scale sugarcane plantations began a conversion from furrow to more efficient drip irrigation methods and a reduction in the amount of acreage dedicated to sugarcane production.
Estimated recharge for central and west Maui declined 44% during the period 1979–2004. During this period, on the leeward (Lāhainā) side of West Maui Mountain, sugarcane cultivation ceased altogether.
The decrease in irrigation has coincided recently with periods of below-average rainfall, creating the potential for substantially reduced recharge rates in many areas. (USGS)
The period 2000–04 had the lowest estimated recharge; irrigation rates during this period were 46 percent lower than during 1926–79, and rainfall was the lowest of any period.
With the closure of HC&S’ sugarcane fields in central Maui, and subsequent stoppage of irrigation over the groundwater aquifer, recharge will be reduced and the groundwater flow system will be affected. (USGS)
Population growth on the Island of Maui has led to an increase in ground-water demand. The resident population on the island increased more than 300% percent during the period 1960–2010: from 35,717 to 144,444 (Maui County)
The ‘Ïao aquifer system is the principal source of domestic water supply for the Island of Maui. Ground-water withdrawals from this aquifer system increased from less than 10-Mgal/d during 1970 to about 17-Mgal/d during 2005.
So, there is concern surrounding declines in ground-water levels and an increase in the chloride concentration of water pumped from wells in the ‘Ïao aquifer system.
Even before the contemplated, and later announced, closure of HC&S sugar cultivation, the State Water Commission designated ‘Īao as a groundwater management area because the 12-month moving average pumping withdrawals exceeded the Commission-established trigger.
The effect of changes in irrigation-enhanced recharge was illustrated on a small scale in Wailua on Kauai, and the drying up of ‘Fern Grotto’ was the result. There, the Kapa‘a irrigation system was built in the 1920s to provide water for approximately 6,000 acres of land under sugar cane.
Up until the sugar company closing, the lower portion has been fed by the Hanamaulu Ditch, which ended at ‘Reservoir 21,’ directly above Fern Grotto. The ferns began growing only after sugar was grown on the land 150 feet above the cave.
Plantation workers built a catch basin for storm runoff that became known as Reservoir 21. Water from the reservoir percolated through the ground and came out on the roof and walls of the cave.
The shutting down of the Hanamaulu Ditch has undoubtedly contributed or even was the principal cause of the drying up on the Fern Grotto. The lack of irrigation water caused the cliff-side ferns to dry up.
A 9-month rejuvenation project involved creation of a second waterfall in the grotto and installation of solar panels to power pumps to bring water from the Wailua Reservoir to the Fern Grotto.
Now, the Fern Grotto is back. Solutions in the central Maui isthmus, the principal source of domestic water supply for the Island of Maui, are not as simple.
A century after Captain James Cook’s arrival in Hawaiʻi, sugar plantations started to dominate the landscape. Sugar changed the social fabric of Hawaii. Hawai`i’s economy turned toward sugar in the decades between 1860 and 1880.
The industry came to maturity by the turn of the century; the industry peaked in the 1930s. Hawaiʻi’s sugar plantations employed more than 50,000 workers and produced more than 1-million tons of sugar a year; over 254,500-acres were planted in sugar. (That plummeted to 492,000-tons in 1995; a majority of the plantations closed in the 1990s.)
So, the Islands have not just lost that last remnant of generations of economic and agricultural activity; Maui must now look at ways to manage and provide for water needs and demands, given the loss of irrigation-enhanced recharge. (Lots of information here is from several USGS reports.)
I was fortunate to have served as the Chair and Director of the Department of Land and Natural Resources and the Chair of the Water Commission, working on these and other related issues.