Yakima Basin Groundwater Study

Last night I went to the USGS presentation on their Yakima basin groundwater study -- one of the most important water-related events I've been to.

The USGS has built what may be one of the most ambitious models the agency has attempted. The computer model (computer models are like giant spreadsheets, with equations that attempt to produce a mathematical description of something, in this case ground- and surface water flows) divides the Yakima River basin into thousands of 1000-foot squares. Beneath the surface grid, the model considers up to 48 underground layers, from the sediment near the surface to the bottom of the Grande Ronde basalt flows.

Like a complicated machine, the model has lots of what amount to switches and valves that can be adjusted. The first step is to try to adjust the switches and valves so that the model spits out an accurate description of what is happening now, and what has happened in the past. Using inputs of precipitation, water management from the reservoirs, weather data, irrigation and other pumpage, crop types, and so on, the model really does produce an accurate -- but not perfect, because that's not possible -- picture of how water behaves.

So far, the model works best on the part of the Yakima River basin downstream from Umptanum and the canyon. It turns out that the upper Kittitas County area is much more complicated that the rest of the basin. This mostly is because the geology is different and more complicated, and because precipitation levels change rapidly over distance. The current model's main water input is based on releases from the reservoirs, but the Upper County's groundwater depends mostly on rain- and snowfall.

The USGS team and their model will be focusing on the Upper County next. Because of the complexity of that area, it seems to me that the model will be more uncertain in there, which means we'll need to understand the role of uncertainty in science. I'll write more about that, probably later today. I've mentioned it before, in my post about making your case.