Estimating the distribution of water quality in two different populations of water masses in a river structure

Abstract

Two populations of river units have been used to estimate cumulative distribution functions of water quality data (pH, total phosphorus and total nitrogen) from the watercourse of Telemark in southern Norway. A population that quantifies the water resource using the concept of standardized river kilometers (referred to as the momentum method) can be compared to a population of ordinary river kilometer units. In order to obtain good estimates of water quality, the sampling population was stratified into more homogeneous sub-populations. Different criteria for stratification, like human activities, topography in the drainage area and flow rates of the rivers, can been compared.

The momentum method gives heavy weights to sample points of high flow rates. A positive correlation exists between parameter values and flow rates. Consequently, the 10 percentiles are higher using the population of momentum units than when using the population of kilometer units.

The momentum method should be used for water quality surveys where the quantitative aspect of the water resource is of interest. A quantification of a water resource by the momentum method is quite “data-intensive” and requires a lot of flow rate measurements.