Every reservoir loses live storage capacity to silt over time, but the rate varies enormously depending on catchment characteristics, upstream land use, and rainfall intensity. This estimator projects capacity loss over the reservoir's operating life at a chosen annual sedimentation rate, giving irrigation departments a planning figure to compare against actual bathymetric survey results.
Why This Is a Projection, Not a Substitute for Measurement
Sedimentation rate is rarely constant year to year, a single severe monsoon can deposit more silt than several normal years combined, and upstream construction or deforestation can accelerate the rate significantly. This tool models a constant compounding rate for illustration. The only way to know actual current capacity is a direct bathymetric survey of the reservoir bed.
| Catchment Type | Typical Annual Sedimentation Rate |
|---|---|
| Forested, stable catchment | 0.2 to 0.5% |
| Mixed agriculture catchment | 0.5 to 1.0% |
| Heavily eroded or deforested catchment | 1.0 to 2.5%+ |
What to Do With This Number
A projected capacity loss figure is useful for budgeting a desilting program, but the actual bed profile from a bathymetric survey tells you where the silt has accumulated, which is just as important as how much. Silt rarely deposits evenly, it concentrates near inlet channels and shallow zones, and that spatial pattern determines where dredging or desilting effort should focus first.
Depth sounding survey underway, the only way to confirm actual capacity against this kind of projection.
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