Some Basics of Water Management—Lecture Notes
There are generally many objectives to balance when operating reservoirs—that’s what
this class is all about. But if your ONLY concern were saving water, there are a few
basics you probably have not thought much about.
1. Reservoirs do not create water. They can be used to change the pattern of flow
downstream of the dam within limits, such as filling reservoirs/reducing flow
downstream in wet years and releasing from reservoirs/increasing flow
downstream in dry years.
2. There is some water lost through evaporation. There can also be exchange with
groundwater aquifers.
3. When reservoirs are full, they spill, so the flows downstream are essentially the
same as if they reservoirs were not there (except for evaporative losses).
4. Reservoirs can only capture water from upstream (water flows downhill). This is
independent of the size of the reservoir. Take, for example, the ApalachicolaChattahoochee-Flint basin. The largest reservoir, by far, is Lake Lanier. This is
also the most upstream reservoir, with only 5% of the drainage basin.
5. “Probability of refill” is therefore an important concept. Show some plots
6. Again, in the context of using reservoirs to save water for droughts, once the
reservoir is full, you lose all additional inflow. This is true unless, of course, you
can capture it downstream.
7. How do you know when a reservoir is TOO low, meaning there is a very real
possibility you will run out of water completely?