The aesthetic value of river flows: An assessment of flow preferences for large and small rivers

Increased demands for water for consumptive and in-river uses have increased the socio-economic values of river flows. Protecting aesthetic quality is an increasingly important aspect of river management. In an online photographic survey showing New Zealand rivers we addressed aesthetic value of flow and the effects of river size or planform on flow preferences of river users. The survey results were used to assess the abilities of observers to distinguish changes in river flow. Survey responses indicated that high flows and minimal bank exposure were preferred in small rivers, and intermediate or low flows and low turbidity were preferred in large rivers. We detected a concave relationship between preference strength and normalised river flow (depicted flow/mean flow). A log-normal model to fit the preference data indicated that preferences increased with normalised flows up to a threshold corresponding to ∼60% of the mean flow. The accuracy of flow estimates by respondents varied with river planform and size. Across the five river reaches tested, median estimates of flow level ranged from 54% to 178% of the actual flows in the survey. Estimates of low flow were generally more accurate than high flow estimate, and estimates for small rivers were more accurate than for large rivers. In view of the limited ability of most observers to estimate river flows accurately, we suggest that river managers use inflection points and other thresholds in aesthetic quality–river flow relationships as a basis for protecting aesthetic value, rather than absolute flow levels or flow statistics.