10 seconds I think is usually good for creating a blurred effect in running water. But I think this creek was running quite slowly so a bit longer perhaps would have been better. I am guessing that you didn't have an ND filter? For a long exposure during the day that is quite useful tool for getting longer exposure times
I am happy with this shot. The shutter speed is 8 seconds. I am still struggling with knowing how long to set the shutter speed and what aperture to choose.. Every week I learn a bit more about my camera and that is rewarding.