Flooding can occur even during the 10 or 20-year recurrence
interval flood flows in some locations along SLO Creek, due to flow constrictions at
bridges and other areas of limited channel conveyance. Denuded banks and erosion can add plant debris and sediment that is later re-deposited downstream. Undermined trees may
topple into the channel in some areas during the next large flood event.
Streambank vegetation can collect debris, reducing channel capacity and deflecting flows against banks.
A set of rainfall-runoff and stream flow computer models that numerically describe the
hydrologic and hydraulic performance of the watershed and stream system was developed
as part of the SLO Waterway Management Plan (2003). The modeling results, along with existing reports of historic flood damage, provide a comprehensive picture of where flooding is likely to occur in the future. The hydrologic and hydraulic models provide information on flood channel conveyance
capacity, flood reoccurrence intervals, and estimates on the extent of floodway. Figure 3-2 of the SLO Waterway Management Plan summarizes the flooding problems that occur along SLO Creek and its principal tributaries.