Opinion ID: 6493113
Heading Depth: 2
Heading Rank: 1

Heading: Na Wai ‘Ehá Water Systems

Text: Na Wai ‘Ehá are the Waihe'e River and Waiehu, Tao, and Waikapü Streams. The Waihe'e River is the principal water source in Ná Wai ‘Ehá; it is about 26,585 feet long, and its watershed covers 4,500 acres. From 1984-2005, United States Geological Survey (“USGS”) data shows streamflow upstream of all diversions as follows: the Q50 4 flow was 34 million gallons per day (“mgd”), the Q70 5 flow was 29 mgd, the Q90 flow was 24 mgd, and the Q100 flow was 14 mgd. The Waihe'e River’s two main diversions are Wai-he'e Ditch and Spreekels Ditch. See Section H.A.3., infra, for more information about the ditches. The two ditches are capable of diverting all of the dry-weather flow available at the intakes, however, even if all the water is being diverted, streamflow immediately downstream of the intakes may exist because of leakage through or subsurface flow beneath the dams at these sites. The dry-weather flow downstream of the intakes is commonly about 0.1 mgd, but the stream may not have continuous mauka-to-makai surface flow. The Waiehu Stream is formed by the confluence of North and South Waiehu Streams; it is about 23,700 feet long, and its watershed covers about 6,600 acres. Gaging stations on both branches of the Waiehu Stream were discontinued in 1917, but USGS used historical data and record-extension techniques to estimate flows above all diversions for North Waiehu Stream from 1984-2005 as follows: the Q50 flow was between 3.1 to 3.6 mgd, the Q70 flow was between 2.3 to 2.7 mgd, the Q90 flow was between 1.4 to 2.7 mgd, and the Q100 flow was 1.6 mgd (as measured in March 1915). For South Waiehu Stream, USGS utilized the same record extension techniques, and estimated the 1984-2005 flows as follows: the Q50 flow was between 2.4 to 4.2 mgd, the Q70 flow was between 1.9 to 2.8 mgd, the Q90 flow was between 1.3 to 2.0 mgd, and the Q100 flow was 1.5 mgd (recorded in July 1913). The Waihe'e and Spreekels Ditches divert water from both North and South Waiehu Streams; in addition, the North Waiehu Ditch diverts from the North Waiehu Stream and the Cerizos Kuleana Ditch diverts from the South Waie-hu Stream. There is extensive channel erosion below the Spreekels Ditch on South Waiehu Stream, with a 12-foot drop in the elevation of the stream just below the diversion, and there is a vertical concrete apron located in Waiehu Stream. Most of the water is diverted from North and South Waiehu Streams at the North Waiehu Ditch and Spreekels Ditch, respectively; due to these diversions and leakage, Waiehu Stream does not flow continuously from mauka to makai. Tao Stream is the second-largest stream in Ná Wai ‘Ehá; it is about 38,000 feet long, and its watershed covers about 14,500 acres. USGS calculated the 1984-2005 flows above all diversions as follows: the Q50 flow was 25 mgd, the Q70 flow was 18 mgd, the Q90 flow was 13 mgd, and the Q100 flow was 7.1 mgd. The two main diversions off the Tao Stream are the Tao-Waikapü/Tao-Maniania Ditches at an altitude of 780 feet, and the Spreekels Ditch at 260 feet. The United States Army Corps of Engineers channelized significant portions of Tao Stream’s lower reaches and hardened the stream bed and banks with concrete for flood control and drainage. About 2.5 miles above the mouth of the Stream, the concrete channel includes a 20-foot vertical drop. USGS estimates that Tao Stream loses 6.3 mgd in reaches downstream of the Tao-Maniania ditch diversion that are not lined with concrete. In absence of ditch return flows or runoff during and following rainfall, Tao Stream is dry and does not flow continuously from mauka to makai. The Waikapü Stream is the southern-most stream and the longest of the four streams; it is about 63,500 feet in length, with a watershed of about 9,000 acres. USGS, using record extension techniques, estimated the 1984-2005 flows above all diversions as follows: the Q50 flow was between 4.8 to 6.3 mgd, the Q70 flow was between 3.9 to 5.2 mgd, and the Q90 flow was between 3.3 to 4.6 mgd. The lowest recorded flow for Waikapü Stream was 3.3 mgd, in October 1912. There are three diversions off the Waikapü Stream: the South Side Waikapü Ditch (also known as the South Waikapü Ditch) near an altitude of 1,120 feet, the Waihe'e Ditch, and the Reservoir 6 Ditch. The Waikapü Stream is commonly dry downstream of all diversions, both because of the diversions and because of infiltration losses into the streambed; the Stream does not flow continuously from mau-ka to makai.
There are three types of ground water in Ná Wai ‘Ehá water systems: dike-impounded, the basal freshwater lens, and perched. Dike-impounded ground waters occur at high elevations; basal freshwater lenses and perched waters occur at lower elevations and closer to the coast. The dikes at higher elevations are low-permeability, so water builds up behind them. The upper reaches of Ná Wai ‘Ehá streams intersect the dike-impounded ground water so the upper reaches have year-round streamflow, even during dry periods. The portions of the stream joined by the dike-impounded water are described as “gaining” because ground water contributes to stream-flow. The basal freshwater lens system is contained in volcanic rocks and sedimentary deposits. Perched water also occurs in the sedimentary deposits. In the lower reaches of the streams where an unsaturated zone exists between the streams’ channel bottoms and the water table, stream waters migrate from the stream beds to the basal lenses, and the streams are described as “losing.” Some of the stream channels intersect the basal freshwater lens near the mouths of the streams, making the streams “gaining” in those areas. The Commission considered the IIFS for Ná Wai ‘Ehá with the WUPA for the high-level dike-impounded ground water. As the Hearings Officer, Dr. Lawrence H. Miike, explained, the Commission decided to combine the issues into one contested case hearing because the water systems are all connected and considering the WUPA and IIFS together would allow the Commission “to get a bigger picture and to be able to try to reach a more rational and reasonable decision. ...” One example of the interconnectedness of the high-level dike-impounded ground water and the surface waters is the tunnel system. Several tunnels tap dike-impounded ground water and discharge directly into the streams. In some cases, denial of a WUPA for dike-impounded ground water results in additional water contributing to streamflow.
There are two primary and two secondary systems that distribute water diverted from Ná Wai ‘Ehá. The primary systems are WWC’s ditch system and HC & S’s reservoir/ditch system. Nine active diversions feed the primary distribution system: two on Waihe'e River, one on North Waiehu Stream, one on South Waiehu Stream, two on ‘lao Stream, and three on Waikapü Stream. There are two major ditches in the system: the Waihe'e and Spreckels Ditches. The WWC distribution system involves eleven registered stream diversions, two major ditches, seven minor ditches, and sixteen reservoirs; HC & S shares in the cost and maintenance of portions of this system. HC & S also operates a diversion intake on South Waiehu Stream at the Spreckels Ditch, a diversion intake on lao Stream at the Spreckels Ditch, and the Spreckels Ditch from Reservoir 25 to its terminus at HC & S’s Reservoir 73. The waters that enter the distribution system travel by gravity flow in primary ditches through uplands into reservoirs that in turn deliver the water into smaller ditches for end use. The secondary systems are the so-called “kuleana” 7 ditches/pipes that either have an intake directly in a stream or receive water from the primary systems and the MDWS water treatment plants. The Commission identified seventeen kuleana diteh/pipe systems. Fourteen kuleana systems are connected to the primary distribution systems; three kuleana intakes connect directly to the streams.