The Colma Creek flood control channel provides flood protection for the communities of South San Francisco, Colma, and Daly City. The 5.4 mile-long earthen and concrete lined channel is maintained by the County of San Mateo Public Works Department. Colma Creek historically experienced very high sediment loads in the 1960s and 1970s when the watershed was under more intensive development. Flood control maintenance for Colma Creek requires periodic sediment removal, culvert clearing and repair or replacement, and minor routine maintenace activities.

The County faced permitting delays to authorize maintenance at Colma Creek because regulatory agencies questioned how sediment removal activities would affect natural processes and sensitive habitats. Horizon was hired in 2013 to conduct technical studies to address these concerns and advance the permitting process. Horizon developed technical studies to identify sediment removal locations and volumes and evaluate potential impacts to sensitive habitat. Horizon also coordinated sediment testing to determine potential disposal and reuse options for excavated sediment. Horizon successfully completed the CEQA IS/MND in 2016 within budget and on schedule; prepared permit applications and supporting documents. Horizon helped the County successfully obtain the needed permits enabling the County to commence maintenance in 2017.