Streamflow trends over the past year at Chehalis River Near Grand Mound 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 116,829 days. The streamflow average over the past 10 days was 311.1 ^cfs, with a day to day variation of about 18.7^cfs.