Practical empirical estimation of evaporation for mining and industrial water balances : application to a South African process dam

Abstract

Direct measurement of evaporation at mining and industrial sites is highly accurate, but often prohibitively expensive, limiting its routine use in operational water balance modelling. This study evaluates a practical, cost-conscious approach for estimating daily evaporation using commonly applied empirical methods. Model performance was assessed by comparison with measured evaporation at both daily and aggregate scales. Among the methods tested, the Hargreaves equation provided a simpler yet sufficiently accurate alternative to the Penman–Monteith equation for operational applications. Sensitivity analysis showed that temperature is the dominant control on evaporation estimates for both methods, while solar radiation additionally influences Penman–Monteith estimates. Prioritising temperature and solar radiation measurements can substantially improve evaporation estimates where monitoring resources are limited. Local rainfall and wind measurements remain necessary to account for spatial variability and non-modelled losses. The results demonstrate that reliable evaporation estimates can be achieved using simplified empirical methods, supporting improved water balance assessments at mining and industrial sites where direct measurements are not feasible.

HIGHLIGHTS • The Penman–Monteith and Hargreaves methods can accurately estimate evaporation in process dams. • The Hargreaves method is a practical, low-cost alternative requiring fewer inputs and simpler computation. • Accurate measurement of temperature and solar radiation is critical. • Prioritising key parameters enables reliable estimates under budget constraints.