The Donald C. Tillman Water Reclamation Plant is in the sepulveda flood control basin, owned by the U.S. Army Corps of Engineers. Risk of flooding at the plant site is reduced by levees and a floodwall. To extend the lease held by the City of Los Angeles, the Corps requires adherence to its vegetation policy, which compels extensive tree removal. The site, however, includes an award-winning Japanese Garden and removal of trees would negatively impact the plant site, Japanese Garden, and surrounding park. Deterministic analyses were conducted to better understand the anticipated performance of the levees, floodwall, and trees in response to flood loading. To save the trees, the City undertook a risk analysis to answer a specific question: Does the presence of trees materially increase the risk from flooding? The risk analysis process, following best practices promulgated by the corps, concluded that trees do not materially increase the risk of damage or loss of life from flooding.
