I'm pretty sure you're right. Fall Chinook, being generally large fish, don't like to enter the dinky creek at the lower Kalama hatchery. In order to secure the fall Chinook hatchery broodstock, the weir was necessary to prevent those fish from just swimming on upstream and spawning in the river, which is still pretty small in the fall. Coho spawn in small creeks and are more than willing to swim up dinky little hatchery creeks.IF!!!!!! I remember right the purpose of the wier is to remove hatchery chinook. The steelhed and coho might be delayed but otherwise unaffected. That said the good coho, "B" runs are the October/November fish which will come in when the water is high and will bypass the weir.
Talking about the lower weir. Not up at the Hatchery.
Anyone feel free to correct me..