As you've already discovered, NAUTIQUE/REWARD isn't effective on this plant. Although REWARD might provide a temporary chemical-mowing effect - it certainly won't kill torpedograss.
Glyphosate will likely do a fair/decent job - depending on how much healthy leaf-surface has emerged above the water's surface.
I'm hesitant to suggest anything in CA due to heavy regulations. But, if I was battling torpedograss here, I'd turn to one of the aquatic imazapyr products (several brands exist), along with a methylated seed-oil (MSO) surfactant.
