Okie boater, I hope all is well with you and you have a good trip to Montana. I will attempt to predict the future based on what I know. Historically the Smith peaks from mid May to mid June. When it is wet and cool like it is now, the peak is shifted a little later. The peak flow, even in dry years is rarely under 500 cfs. Right now the Smith is running at 140 cfs. The current flow is almost all ground water recharge. Later this week the upper basin is supposed to get precipitation on Thursday and Friday. It will come up at some point. The question is how high for how long.
Stone is right that the basin has not got its fair share of the moisture we have seen this spring in the rest of Montana. In early April it looked like the year was going to be a disaster. It has continuously improved since. Here is the latest snow water map.
mt_swepctnormal_update.pdf (usda.gov)
Unfortunately the Smith is lumped in with two larger drainages, the Judith and the Musselshell. The trend is very promising. On April one snow water was at 71%. Now it is at 112%. The Smith change is probably lower than that. Normally the Smith has 95% of its snow water on April 1, and the absolute peak is on April 15. This year we have got more water later in the winter/spring, after a very dry year. At some point this water will increase flow.
20 some years ago the government did a detailed study of water in the Smith river basin. here is the summary of the report:
The model enabled a detailed evaluation of the components of the water budget within the Smith River watershed during the water year 1996–2008 study period. During this study period, simulated mean annual precipitation across the Smith River watershed was 16 inches, out of which 14 inches evaporated or transpired and 2 inches left the basin as streamflow. Per the precipitation-runoff model simulations, during most of the year, surface runoff rarely (less than 2 percent of the time during water years 2002–2008) makes up more than 10 percent of the total streamflow. Subsurface flow (the combination of interflow and groundwater flow) makes up most of the total streamflow (99 or more percent of total streamflow for 71 percent of the time during water years 2002–2008).
As you can see most of the water that falls on the drainage never makes it to the river. As the climate gets hotter and drier, even less will be making it to the river. There is another problem that is impacting flow. As the river has become less reliable, the irrigation users in the upper basin are drilling wells and using ground water that will impact the base flow of the river.
The basin is about 2000 square miles in size, and most of the flow comes from the upper half. Only about 100 square miles of the upper basin is irrigated, but that has a major impact. Here is a great map of the total basin.
Location of Smith River watershed, Montana | U.S. Geological Survey (usgs.gov)
Well now you know what I know. My guess is that we will have a nice little season of decent flow in early June. Have fun on the river.
