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Flood Source Description of the Flood Problem Belmont Creek and Holly Street Channel Overflows from Belmont Creek in the City of Belmont flow generally toward Francisco Bay. This overland flow can follow numerous routes, and the entire area on the bayside of the railroad tracks is subject to shallow flooding. At the railroad, the overland flow is split, and the greater part is diverted to the east. Additional overflow occurs near Harbor Street and Old County Road at a railroad loading spur. The Bayshore Freeway and Holly Street off -ramp form a barrier to the easterly flow, causing shallow ponding in the Industrial Way area. This ponding has been greatly reduced by recently completed drainage projects. San Francisquito Creek San Francisquito Creek overflows at two locations in the City of Menlo Park. The overflow travels east toward the bay along streets leading away from the creek channel. At the Bayshore Freeway, this shallow flooding crosses into the county area and continues toward the bay. There are no other spills from San Francisquito Creek into the county area. Tidal flooding from the bay during the 1-percent annual chance flood can overtop the levee system in the City of East Palo Alto and cause flooding in the residential area adjacent to San Francisquito Creek. Flooding has resulted in this area because of inadequate or nonexistent stormwater facilities. Montara Creek Montara Creek is generally confined to its channel, with overtopping at most culvert crossings. The culvert at Harte Street is heavily silted, forcing the water out of the channel and over the road; a few residences are affected. The embankment at State Highway 1 forms a dam, resulting in deep flooding; however, no existing structures are affected. San Vicente Creek San Vicente Creek overflows to the north at Etheldore Street, causing shallow flooding through several existing structures adjacent to State Highway 1 before the overflow returns to the channel along Cypress Avenue. Additional flooding occurs near the ocean front because of inadequate culvert capacity. Denniston Creek Denniston Creek is contained within a well-defined channel until it reaches State Highway 1, where limited culvert capacity results in shallow overflow and ponding southward behind the highway to a low point near Sonora Avenue, where it flows overland to the ocean. The channel through the developed part of Princeton is overgrown and culverts are of limited capacity; however, the resulting flooding is minimal. El Granada Creek El Granada Creek consists of a very shallow channel through the most developed oceanside area of the county. Undersized culverts in the channel In many places cause general flooding of roads and residences near the creek. This flooding is contained by the remnants of the natural floodplain through the community. Woodhams, La Honda, Alpine, and San Gregorio Creeks All creeks in the La Honda community flow in well-defined and often steep channels. Flooding occurs across various stream terraces that are adjacent to culverts or channel restrictions. On San Gregorio Creek, a combination of meandering channel and numerous private bridges creates similar terrace flooding situations. Pescadero and Butano Creeks Pescadero and Butano Creeks are in a river valley formed by two large drainages. Each creek has a well -defined channel that meanders through a broad floodplain bounded by hills on either side. This floodplain has little gradient and therefore is inundated by overflows from Pescadero Creek and joining flows of Butano Creek. Most of the Town of Pescadero is in this floodplain and is inundated during floods. The U.S. Army Corps of Engineers estimated the cost of damage in Pescadero caused by the December 1955 flood to have been $352,000, including rescue and emergency efforts. The 1998 flood brought record floods to this watershed. Over 6 inches of rain fell over two days and a peak flow of 10,600 cfs was recorded at the USGS gage on Pescadero Creek. High water marks taken after the flood show a flood elevation of 14.6 feet just downstream of the Pescadero Creek Road bridge. Pacific Ocean Flooding from the Pacific Ocean at Miramar and Martins Beaches is typically associated with the simultaneous occurrence of very high tides, large waves, and storm swells during winter. Ocean-front development has not been compatible with the natural instability of the shoreline and the intense winter weather. Tsunamis create some of the most destructive natural water waves. Storms from the southwest produce the storm pattern most commonly responsible for the most serious coastal floods. Strong winds and high tides that create storm surges are also accompanied by heavy rains. In some instances, high tides back up river flows, causing flooding at river mouths. In January 1978, storms emanated from a more southerly direction than normal, and some of the better-protected beaches were damaged. Jetties and breakwater barriers were overtopped and, in some cases, undermined. Direct wave damage occurred to many beachfront homes. Accelerated erosion coupled with saturated ground conditions and rain weakened the foundations of homes on the top of beach bluffs. Seawalls and temporary barriers failed to protect beach front properties. The winter of 1983 brought an extremely unusual series of high tides, storm surges, and storm waves, which caused considerable damage along the northern California coast. 11-9