Hills, creeks and the way water moves
The Berkeley hills rise steeply behind the flatter neighborhoods, and several creeks run down toward the bay, some of them buried in culverts under streets and yards. In winter, runoff from the slopes can reach lower properties quickly.
Drainage is therefore a daily topic. Roof water, patio runoff and slope runoff all need to go somewhere. Near a creek, there may be setback rules, and altering flow can bring city or county review. The Hayward Fault also runs along the base of the hills, so walls and structures are built with movement in mind.

