Waimanalo Watershed Restoration Project

View of the misty Koʻolau Mountains

The Waimānalo area is truly one of the most beautiful spots on Oʻahu, with a rural atmosphere comprised of nurseries, small fruit and vegetable farms, and horse boarding facilities. The Waimānalo Watershed is part of the Koʻolaupoko watersheds on the Windward side of Oʻahu. The Watershed is approximately 3800 acres in size and includes the Waimānalo and Kahawai Streams.

Studies conducted in 1999-2000 showed high levels of nutrients and sediments in the stream. Further studies resulted in the Waimānalo Watershed being listed in the 2004 Final Report of Impaired Waters in Hawaiʻi prepared under the Clean Water Act 303(d) report for excess nutrients, turbidity and suspended solids. The reports do not disaggregate nutrient or sediment sources by land type, land use, or tributary.

For a total of three project phases spanning 2009-2021, Oʻahu RC&D worked with landowners and other partners to implement best management practices geared towards reducing nutrients, erosion and sediment delivery in the Waimānalo Watershed mauka of Kalanianaole Hwy. Surveying and water sampling throughout sections of the watershed helped provide direction on potential pollutant sources, and focused land treatments for farms, homes, roads, and streams. Utilizing the best conservation planning concepts, farmers received financial support to install buffers, vegetative barriers and other practices to reduce soil erosion. 

Generous support for this project came from the Clean Water Act and the Hawaii Department of Health.

BMP Showcase

Cooperators in these restoration projects transformed sections of their properties to improve and preserve their soil and water resources, which was documented in before and after photos.

A bare-soil waterway has been converted into a lined waterway to reduce erosion where runoff waters have a propensity to erode the soil while allowing for occasional vehicle crossing and ease of maintenance.

A vegetative barrier was established along a property border fenceline to filter and slow runoff that enters the property.

A cover crop mix of daikon radish and sunn hemp was well established in a field following deep tillage to remediate the soil for crop production. These practices used in combination break up hard compact soil, while also improving soil health and reducing erosion.