# Wahiawa Dam (Wilson Reservoir) ## Overview Wahiawa Dam is a government‑owned earthfill dam situated in the central plateau of Oʻahu, Hawaiʻi. The dam creates Wilson Reservoir, locally referred to as Wahiawa Reservoir, which serves multiple purposes including agricultural irrigation, flood control, and recreational activities such as fishing and boating. ## History - **Early 1900s:** The need for a reliable water source for the expanding pineapple and sugarcane plantations in central Oʻahu prompted the Territorial Government of Hawaiʻi to study potential dam sites. - **1905:** Preliminary surveys identified the Wahiawa Stream valley as an optimal location due to its favorable topography and watershed characteristics. - **1908‑1912:** Construction of the dam commenced under the supervision of the Hawaiʻi Territorial Board of Agriculture and Forestry. The project employed local labor and utilized basic earthmoving equipment of the era. - **1913:** The dam was completed and the reservoir began impounding water, marking one of the first large‑scale water storage projects in the Hawaiian Islands. - **1930s‑1940s:** The reservoir’s water supported the peak of Oʻahu’s plantation economy, providing irrigation for over 20,000 acres of sugarcane and pineapple fields. - **1970s:** With the decline of large‑scale plantation agriculture, the dam’s role shifted more toward municipal water supply and recreation. - **2000s‑Present:** Periodic safety inspections and upgrades have been carried out to meet modern dam safety standards, including spillway reinforcement and seepage control. ## Construction and Design - **Type:** Homogeneous earthfill dam with a central impervious core. - **Height:** Approximately 55 feet (16.8 m) above the streambed. - **Length:** About 1,200 feet (366 m) along the crest. - **Volume:** Roughly 180,000 cubic yards (138,000 m³) of fill material. - **Spillway:** Unlined concrete chute spillway designed to pass the probable maximum flood (PMF) with a capacity of around 12,000 cubic feet per second (cfs). - **Outlet Works:** A multi‑level outlet tower equipped with slide gates for regulated releases to Wahiawa Stream and downstream users. ## Wilson Reservoir (Wahiawa Reservoir) - **Surface Area:** Approximately 210 acres (85 ha) at full pool. - **Storage Capacity:** About 7,500 acre‑feet (9.25 million m³) of water, qualifying it as a "major dam" under the National Inventory of Dams criteria. - **Elevation:** The reservoir’s normal water surface elevation is roughly 840 feet (256 m) above mean sea level. - **Uses:** - Irrigation for diversified agriculture in the Wahiawa and Whitmore areas. - Recreational fishing (stocked with largemouth bass, bluegill, and channel catfish). - Limited non‑motorized boating and kayaking. - Habitat for native aquatic species and migratory birds. ## Purpose and Benefits 1. **Agricultural Irrigation:** Supplies water to roughly 15,000 acres of farmland, supporting crops such as seed corn, vegetables, and ornamental plants. 2. **Flood Mitigation:** Attenuates peak flows in Wahiawa Stream, reducing flood risk downstream in Wahiawa town and the surrounding lowlands. 3. **Recreation:** Provides a scenic venue for shoreline fishing, picnicking, and wildlife observation. 4. **Water Quality:** Acts as a settling basin, reducing sediment transport to downstream ecosystems. ## Environmental and Social Impact - **Positive:** The reservoir enhances local biodiversity by creating wetland habitats; it also supports community recreation and contributes to the region’s agricultural economy. - **Challenges:** Sedimentation has gradually reduced storage capacity; ongoing dredging and watershed management programs aim to mitigate this. - **Cultural Significance:** The dam and reservoir lie within traditional Hawaiian lands; consultation with Native Hawaiian organizations is part of modern operational reviews. ## Management and Oversight - **Owner/Operator:** State of Hawaiʻi, Department of Land and Natural Resources (DLNR), Division of Boating and Ocean Recreation. - **Regulatory Oversight:** Subject to periodic inspections by the Hawaiʻi Dam Safety Program and the Federal Energy Regulatory Commission (FERC) for hydroelectric considerations (though no power generation is currently present). - **Maintenance Activities:** Routine vegetation control on the dam face, seepage monitoring, spillway gate testing, and emergency action plan drills. ## Notable Facts - Wahiawa Dam was among the first dams built in Hawaiʻi specifically for agricultural water supply. - The reservoir’s name "Wilson Reservoir" honors Henry E. Wilson, a territorial engineer who contributed to early water‑resource planning in Hawaiʻi. - Despite its modest height, the dam’s storage capacity places it in the "major dam" category due to the large volume of water it holds. - The surrounding area is a popular spot for birdwatchers, with sightings of the Hawaiian stilt (aeʻo) and migratory shorebirds. ## Future Outlook Plans are underway to enhance the dam’s seismic resilience, update the outlet works for better flow control, and explore low‑impact hydroelectric potential to generate renewable energy for nearby facilities. Community engagement initiatives aim to balance water resource management with cultural preservation and recreational access.