Streamflow trends over the past year at Cowlitz River At Castle Rock in an interactive calendar format. View seasonal patterns on the river and see how an evolving climate has affecting streamflow levels over the past year. Click on any day to see what the streamflow was for that day, or sign up for a free account to view data for the past 121,664 days. The streamflow average over the past 10 days was 3138.0 ^cfs, with a day to day variation of about 609.5^cfs.