Figure 4.6.1 Destratification induced by bubble column
In general, the system design is based on the volume of water to be fully mixed, a representative
temperature profile, and the stability of the reservoir (the potential energy of the mixed system minus the
potential energy of the stratified system). The pneumatic-system must input enough energy into the
reservoir to overcome the computed stability and thereby destratify the region of interest.
Davis (1980) also presented guidelines for a total or partial-lake destratification system. This
design relies on a single perforated pipe (linear diffuser) to create a bubble curtain in the water column
to induce vertical mixing. The guidance presented in the following paragraphs is a summary of the
procedures outlined by Davis (1980) used for sizing a system to totally destratify a lake.
The first step in the design process is the computation of stability of the reservoir under a
particular stratification. For a given temperature profile and reservoir bathymetry, the stability of the
volume to be destratified, defined as the potential energy of the mixed system minus the potential energy
of the stratified system, is determined. Davis recommends use of a temperature profile with a 4oC
change through the thermocline for this process.
The total theoretical energy required to destratify the system is based on this stability and the
solar and wind energy input to the reservoir volume. Davis (1980) provides guidelines for estimating
the extent of solar and wind input into the system.
Next, the quantity (flow rate) of air required to destratify the reservoir volume is calculated
based on the total theoretical energy, the time required to destratify the volume, and the depth of water
above the perforated pipe. Davis (1980) recommends a minimum air flow rate of 20 L/sec.