1.5 miles in length at the foot of the mountains: the Arroyo Seco stream is a natural channel flowing through an alluvial flood basin in the Devil's Gate Dam reservoir area.
Hahamongna Watershed Park is the most important area for natural resources management in the watershed, including habitat, sediment, open space, and power transmission, but with particular importance for water resources. The water resources management issues in Hahamongna are very delicate and critical to the environment, people and habitat. Hahamongna serves as the main groundwater recharge site throughout the watershed, and throughout the region. Contamination of groundwater from the Jet Propulsion Laboratory has been a major obstacle for providing clean drinking water to residents relying on Raymond Basin Groundwater as a source of fresh, potable water. The watershed area of Hahamongna is about 30 square miles, draining the entire natural upper watershed, and the urban areas of La Canada, Altadena and Pasadena. Storm water from these urban areas impacts the habitat and recreational activities of Hahamongna. Integrating storm water management with groundwater recharge will be a "win win" for water resources in Hahamongna, and will set the bar for MS4 permit projects. The opportunity for storm water remediation and groundwater recharge culminates perfectly with the potential for wetland habitat restoration in Hahamongna Watershed Park.
The Least Bell's Vireo, an endangered bird species, has been recently identified to be seasonally nesting in Hahamongna. With the LA County Sediment Removal and Management Program set be begin shortly, along with the JPL parking structure, Pasadena's formerly titled "Multi-Benefit/Multi-Use" project, the Arroyo Seco Canyon Project and other development projects in the area, the potential for disturbing the birds of Hahamongna is quite large. Hahamongna is one of the best locations for bird habitat in Southern California, and a project to ensure the preservation of high quality bird nesting habitat is needed immediately.
Hahamongna is the interface between a wild, scenic, mountainous and mostly natural river, and the concrete lined, high velocity, storm drain fed river of the Los Angeles urban plane. The river habitat should be capable of providing aquatic habitat, native vegetation, natural sediment dynamics, clean and fresh water, and should also be accessible to recreational users of Hahamongna. A key ingredient in these goals is the riverside canopy providing shade, habitat, stability and aesthetics to a natural open space area that is accessible to millions of LA County residents.