Sac Valley Hydro Trip

A couple days ago, I tagged along on a hydro fam trip conducted by Cindy, the hydrologist for the Sacramento NWS office. She proved to be a true expert in the field; in addition to knowing the river basin cold, she knew the mechanical workings of every river gauge, weir system, and floodgate operation. I had no idea how complex-and efficient- the Sacramento valley flood control system is. It involves a myriad of dams, weirs, bypass channels, and levees. The system has been essentially complete for 60-80 years, though the first levees in the region date from 1862, right after the wettest water year in San Francisco history basically turned the Sac valley into a huge lake. This pic shows the outfall gates at Knights Landing. These gates separate runoff from the creeks draining the mountains to the west from the Sacramento River. Along with a system of pumps, they provide both flood control and irrigation water for the surrounding area.

Here, Brooke is presenting the Sacramento river gage at Colusa. This is the only gage that has the monitor and flood stage posted, along with a digital readout of the current stage. Great idea! (the digital readout is working but wasn't visible in this picture). Why isn't it done in more places? Basically because most gages are in much more secluded areas; this one is right next to the bridge over the river in the town where many people pass by every day. The hydro office and the local farmers have coordinated very efficiently, and most local people know exactly what stage of the river will cause flooding of their land.

This is the Sacramento weir, adjacent to the river just upstream from the city. There is a system of weirs and bypass channels farther upstream that is designed to protect valley cities and towns from high water, but when the water REALLY gets high, this weir is opened to protect Sacramento from flooding. It allows huge amounts of excess water to flow into the Yolo bypass west of the city, thence into San Francisco Bay. There are 48 gates in the weir; the last time they all had to be opened was in 1997 during the massive flooding associated with a major Pineapple express event that dumped torrential rain from sea level up to 10 thousand feet elevation. Amazingly, the gates have to be manually opened, and it's a media event when this happens. The system was implemented in the 1930s and has effectively protected Sac from major flooding for 70 years. In this picture, the river is a couple hundred yards to the right.