Since the first settlers built buildings on the alluvial plain of Alameda Creek, floods were something that had to be dealt with. Even in the early days, some form of dikes were built to try and keep Alameda Creek from affecting homes and farm land. Normally Alameda Creek is a mild stream, but after a few days of rain, it can become a raging torrent. Anybody that has driven through Niles Canyon during the rainy season can attest to how much higher the creek is.
It was not until the 1950s that any major work was done on taming Alameda Creek. The Alameda Flood Control Channel was built in the 1950's to 1960's. This channel prevented Alameda Creek from flooding Niles, Fremont, and Union City.
The last flood recorded in Union City was in December, 1955, just before Christmas. After three days of rain, Alameda Creek rose 20 feet as it passed by Niles. A 50-foot breach in a levee allowed waters to enter Alvarado up to four feet deep in places. The levee was suspected to break, so Sheriff's were in place to notify Alvarado residents in time to evacuate. A total of 15 square miles of the area was flooded. National Guard troops were driving through Alvarado in jeeps helping those that needed evacuation. The start of the Alameda Flood Control Channel near Lowry Road kept that area from flooding.
What helped Alvarado was that a levee break near Niles and Centerville let flood waters flow into one of the 80 feet deep gravel pits, filling it in 4 hours. Once the water started flowing in to the gravel pit, the water under the bridge on Decoto Road dropped two feet.
Four days after the flood most Alvarado residents were still not able to get back to their homes. It took over a week for the flood water to recede in some places. Most residents stayed with family and friends until the waters receded.