| Intermittent streamflow is a common
occurrence in permeable catchments, especially where there are pumped
abstractions to water supply. Many rainfall-runoff models are not formulated so
as to represent ephemeral streamflow behaviour or to allow for the possibility
of negative recharge arising from groundwater pumping. A groundwater model
component is formulated here for use in extending existing rainfall-runoff
models to accommodate such ephemeral behaviour. Solutions to the Horton-Izzard
equation resulting from the conceptual model of groundwater storage are adapted
and the form of nonlinear storage extended to accommodate negative inputs, water
storage below which outflow ceases, and losses to external springs and
underflows below the gauged catchment outlet. The groundwater model component is
demonstrated through using it as an extension of the PDM rainfall-runoff model.
It is applied to the River Lavant, a catchment in Southern England on the
English Chalk, where it successfully simulates the ephemeral streamflow
behaviour and flood response together with well level variations.
Keywords: groundwater, rainfall-runoff model, ephemeral stream, well level,
spring, abstraction |