Water Quality Stations
The usefulness of a water supply depends, to a large degree, on its chemical quality. Observations of
chemical quality, for toe purposes of this guide, consist of periodic sampling of water at stream-gauging
stations and analyses of the common chemical constituents. The number of sampling points in a river depends
on the hydrology and the water uses. The greater the water quality fluctuation, the greater the frequency
of measurement required. In humid regions, where concentrations of dissolved matter are low, fewer
observations are needed than in dry climates, where concentrations, particularly of critical ions such
as sodium, may be high.
Where, ρ(0) is the correlation corresponding to zero distance and d0 s the correlation radius or distance
at which the correlaTion is ρ(0)/). Theoretically, ρ(0) should equal to unity but is rarely found so in
the practice due to random errors in precipitation measurement and micro climate irregularities over an
arear The variance of those random errors has been given by Kagan (1966) as:
where σh2 is the variance of the precipitation time series at a fixed point. The quantities ρ(0) and d0
provide the basis for assessing the accuracy provided by a network.