Dam Tailwaters - Hydro-Environmental Analysis: Freshwater Environments - page 504

Central aeration

Without aeration

Distributed aeration

Peripheral aeration

With aeration

14

Aeration discontinued

12

Aeration started

Aeration periodically
disrupted for testing

10

8

Ta rget downstream DO-6 mg L -1

6

4

Scrollcase DO, historical mean
Scrollcase DO, 1996 samples
Downstream DO, 1996 samples

2

0

1 2 3 4 5 6

Month

7 8 9 10 11 12

FIGURE 18.10 Autoventing turbine for Norris Dam, Tennessee Valley Authority, and an illustration of a bubble
plume and DO concentrations with and without reaeration. (From Hopping, P., Patrick, M., Thomas, B., and Joseph,
C., Update on development of auto-venting turbine technology, Tennessee Valley Authority, Norris, TN, nd.)

18.4.1.4 Weirs
Small dams and weirs may be built below the main dam of some reservoirs to partially mitigate their
impact. One example is a regulation dam, which can be used to create a pool below the reservoir.
Regulation pools are often used to smooth out or attenuate the dam lows, such as the pulses from
peaking hydropower facilities. Downstream weirs are also used for reaerating the releases, such as
using aerating weirs. Aerating weirs are passive systems that typically induce turbulent mixing and
increased reaeration using waterfalls. Here, the spillage and pressure difference is usually not enough