Thermal stratification is the root cause behind almost every reservoir source-water problem — anoxia, metal release and cyanobacterial blooms all follow from it. We characterise the stratification regime across a full annual cycle, quantify the energy holding it in place, and carry that analysis through to a verified, compliance-documented destratification design.
Stratification is not assumed — it is measured and modelled. We resolve the temperature structure, quantify its stability month by month, and only then derive whether destratification, hypolimnetic oxygenation or a hybrid is the right intervention. The design is the conclusion of the assessment, not its starting point.
Explore Our ProcessA density structure set by temperature, held in place by buoyancy, and broken only by enough mixing energy
Spring warming creates a buoyant epilimnion over a cold hypolimnion, separated by the metalimnion where temperature — and therefore density — changes most sharply. That thermocline is a near-rigid barrier to vertical exchange: oxygen from the surface cannot reach the bottom, and the hypolimnion is left to deplete.
Water density peaks near 4 °C and the temperature–density relationship is non-linear, so a few degrees across the metalimnion can store a large amount of potential energy. The strength of the barrier is captured by the buoyancy (Brunt–Väisälä) frequency, the natural oscillation frequency of a displaced parcel.
Wind stress, surface cooling and inflow momentum set the mixed-layer depth and can tilt or erode the thermocline. The Wedderburn and Lake numbers compare that forcing to the stratification’s resistance — predicting upwelling, internal seiching and whether natural mixing will ever reach the bed.
Summer layering, density-driven overturn in spring and autumn, and the inverse stratification that protects life under winter ice
Deeper, cooler water has a lower saturation vapour pressure, so it evaporates more slowly than a shallow pond.
The warm, buoyant, wind-mixed surface layer heated by the sun — here about 22 °C (72 °F).
The sharp density gradient that blocks vertical exchange and seals the bottom water off from the atmosphere.
In spring and autumn the column becomes isothermal and density-driven overturn mixes it top-to-bottom, re-oxygenating the hypolimnion.
The cold, dark bottom layer (~14 °C / 58 °F). Re-oxygenation here restores benthic habitat and holds iron, manganese and phosphorus in the oxidised sediment.
Under ice, a ~4 °C (39 °F) dense bottom layer — water’s density maximum — insulates fish and benthos through the freeze.
As ice melts and the surface warms toward 4 °C — water’s density maximum — the whole column reaches near-uniform density. Light wind then mixes it completely, recharging the deep water with oxygen.
Continued heating builds a warm, buoyant epilimnion over a cold hypolimnion, separated by the thermocline. Vertical exchange stops and the isolated bottom water begins its slow slide toward anoxia.
Surface cooling erodes the thermocline until the column is again isothermal; convective overturn mixes the lake top-to-bottom, re-oxygenating the hypolimnion and returning nutrients to the surface.
Under ice, the densest water (~4 °C) sits at the bottom with colder, lighter water above. This stable inversion insulates overwintering life — until spring melt resets the cycle.
The buoyancy frequency N² = −(g/ρ)(dρ/dz) measures the local strength of the density gradient; integrated over depth it gives the Schmidt stability S = (g/A₀)∫(z − zv)[ρ(z) − ρ̅]A(z) dz — the work per unit area needed to mix the column to uniform density. The Lake number LN then weighs that stability against the wind moment to judge whether wind alone can overturn the lake, and the Wedderburn number W predicts metalimnion tilt and upwelling at the upwind shore. These three numbers, computed over the surveyed hypsographic curve A(z), tell us exactly how much buoyancy flux a diffuser must inject and from what depth — turning a temperature profile into an air-flow specification.
A continuous chain from first survey to commissioned, verified plant — nothing assumed, everything evidenced
The depth–area–volume curve is captured first — every stability integral and mixing-energy figure is computed over this geometry.
A thermistor string at the deepest point logs the temperature structure at fine vertical resolution, resolving the epilimnion, metalimnion and hypolimnion through the season.
Schmidt stability, Lake and Wedderburn numbers are computed month by month, establishing the onset, peak and breakdown of stratification and the latest defensible start date for mixing.
The buoyancy flux required to erode the thermocline within a target window is derived from a validated bubble-plume model and set against the stored stability.
Diffuser depth, manifold layout, air-flow rate and blower duty are sized from the energy budget — engineered to the real basin, with a documented safety margin.
Surface-to-bed ΔT and dissolved-oxygen targets are defined, then confirmed in commissioning and tracked against the pre-aeration baseline through the operating season.
Every stage produces an auditable record, mapped to the relevant drinking-water regulations
The full set of assumptions, survey data, temperature profiles and stability calculations behind the design — a traceable record of how the intervention was chosen.
Schmidt-stability time-series, Lake and Wedderburn numbers and the bubble-plume sizing, presented so a third-party reviewer can reproduce them.
How the design supports compliance with the applicable framework — UK Water Supply (Water Quality) Regulations and DWI guidance, EU DWD 2020/2184, the Australian Drinking Water Guidelines and WHO recommendations.
The parameters, depths and frequencies that demonstrate the system is delivering full mixing, with defined acceptance criteria for commissioning sign-off.
As-built records, performance test results and the measured stratification response confirming the design intent has been met.
The seasonal operating protocol, run-hour and energy logging, and the annual reporting template for ongoing regulatory assurance.
What stratification does to the hypolimnion — redox-driven metal and nutrient release, assessed through to a compliant design.
Read MoreHow the stable surface layer feeds blooms — toxin and geosmin/2-MIB risk assessed and designed out.
Read MoreBubble-plume sizing, diffuser configuration and seasonal operating protocols for reservoir mixing.
Read MoreReynolds & Bauhm resolves the temperature structure, quantifies its stability across the season, and carries the analysis through to a verified, fully documented destratification design.
Our expertise spans multiple industries with sector-specific water treatment solutions.