Right on, Fishteck.
The Alberta Electric System Operator ("AESO"), who administer the wholesale electricity market in Alberta, publish the hourly wholesale price for electricity in the province here:
http://ets.aeso.ca/
Go to the "Historical" tab, and select "Pool Price". Then enter the date range of interest, and up pops the hourly wholesale price history.
Generally, there is a materially higher hourly electricity price during the day, than at night, as electrical load in the province correlates strongly with daily human activity (household, work, etc., vs. sleeping at night). Hence the pattern in the Bow hydro flows you show above - flow the water (and thus generate electricity) during the day, when the price is higher, and cut back at night. Water in these relatively small reservoirs is valuable/scarce, and hence its value in the form of electricity is to be maximized in accordance with hourly electricity prices.
The further bad news is that with all the wind generation we are adding in this province, this will increase electricity price volatility (due to the fact that wind energy generation is intermittent, and somewhat unpredictable - cannot be controlled/matched to load). Hence, when the wind blows at night, when we are generally surplus electricity supply anyways, it pushes down the price. Conversely, when demand is high and the wind isn't blowing, price shoots up. In Feb this year, through the cold, wind generation was almost nonexistent in Alberta - and we had very, very high electricity prices accordingly.
So as more wind adds to electricity price volatility, the economic driver to screw with these hydro flows to take advantage of that peak electricity pricing will only increase. Coupled with the TransAlta hydro PPA's expiring in 2020, this could be a "perfect storm" for even more jacking around with these hydro facilities, with further detrimental effects to the fisheries.