Depending on where you live in Marin, there may be local requirements governing drainage from new construction. Local codes usually follow basic California and case law regarding water rights. Typically downstream owners must accept the runoff flowing in natural channels, including peak storms. However, if an upstream owner has diverted stormwater from another water course, you may have some recourse for downstream damage. The first thing is to assess the nature of any upstream changes (if any). As a civil engineer and real estate broker, I've evaluated a lot of stormwater issues in the Bay Area, so email me with any specific questions.