March 1, 2017

Waiahi Hydroelectric Plant Assessment

Dr. Parham recently completed a hydropower assessment in Hawaii titled:

Assessment of the environmental impact of the Upper and Lower Waiahi Hydroelectric Plants on the native stream animals with respect to habitat changes, barriers to migration, and entrainment using the GIS model-based Hawaiian Stream Habitat Evaluation Procedure

Kaua’i Island Utility Cooperative (KIUC) operates the Upper and Lower Waiahi Hydroelectric Plants in the Wailua River Watershed and is currently seeking to convert from an annual lease to a 65-year lease for water rights. The Hawaii Division of Aquatic Resources (DAR) recommended that the Hawaiian Stream Habitat Evaluation Procedure (HSHEP) be applied to the Wailua River to provide quantification of the amount and distribution of native stream animal habitat and the impacts on native stream animals’ habitat resulting from the Upper and Lower Waiahi Hydroelectric Plants. Two scenarios were to be compared with the HSHEP model:

  1. To assess suitable habitat in the situation with the hydropower plant and other major infrastructure and land use conditions as they currently exist, and
  2. To assess suitable habitat with the hydropower plant removed and all other conditions the same.

Eight species of native stream animals were selected for the purposes of quantifying habitat availability in Wailua River. The list includes five species of fish, two species of crustaceans, and one species of mollusk. This group contains the characteristic amphidromous stream animals found in Hawaiian streams.

Results from the HSHEP model suggest that the non-climbing stream fishes, Stenogobius hawaiiensis and Eleotris sandwicensis, the native shrimp, Macrobrachium grandimanus, the climbing fish, Lentipes concolor, Awaous guamensis and Sicyopterus stimpsoni and Neritina granosa (mollusk) had no or little habitat lost due to the hydropower facilities and thus none of these species were expected to be negatively influenced in the future by the hydropower facilities. The majority of habitat units predicted in the HSHEP model to be lost as a result of the Upper and Lower Waiahi Hydroelectric power plants systems involved habitat for the native mountain shrimp, Atyoida bisulcata. The hydropower system was predicted to eliminate 9.7% of the total amount of habitat found in the Wailua River system for this species.

Entrainment of stream animals is predicted by the HSHEP model to be the greatest impact for the Upper and Lower Waiahi Hydroelectric power plants and associated water collection systems and therefore actions to limit entrainment would be beneficial to stream animals. The main diversions on the North Fork, ‘Ili’ili’ula, Waikoko, Waiaka, and Waiahi Streams all divert a large percentage of low to moderate flows. As a result, most downstream drifting larvae will be entrained in the diversion system. The single most influential barrier in the HSHEP model was Wailua Falls on the South Fork of the Wailua River. It essentially eliminated passage for all native amphidromous species with the exception of Atyoida bisulcata.

  1. While this project was not designed to look at ways to improve or optimize the current operation of the Upper and Lower Waiahi Hydropower system, two primary actions could be recommended for improving stream animal populations associated with the hydropower facility.
  2. Optimize the location and amount of water diverted and design permanent downstream water releases within the diversion system in order to maximize habitat and aid passage for Atyoida bisulcata while retaining current diversion quantities. The use of this HSHEP model for Wailua River would be an excellent resource to aid in optimizing downstream releases by testing various scenarios.Reduce entrainment of Atyoida bisulcata into the generation facilities to avoid mortality associated with passage through the turbines.