Abstract
Lowland rivers and shallow aquifers are closely coupled and their interactions are crucial for maintaining healthy stream ecological functions. In order to explore river–aquifer interactions and lowland hydrological system in three Belgian catchments, we apply a combined approach of baseflow separation, impulse response modelling and time series analysis over a 30–year study period at catchment scale. Baseflow from hydrograph separation shows that the three catchments are groundwater-dominated. The recursive digital filter methods generate a smoother baseflow time series than the graphical methods, and yield more reliable results than the graphical ones. Impulse response modelling is applied with a two–step procedure. The first step where groundwater level response is modelled shows that groundwater level in shallow aquifers reacts fast to the system input, with most of the wells reaching their peak response during the first day. There is an overall trend of faster response time and higher response magnitude in the wet (October–March) than the dry (April–September) periods. The second step of baseflow response modelling shows that the system response is also fast and that simulated baseflow can capture some variations but not the peaks of the separated baseflow time series. The time series analysis indicates that components such as interflow and overland flow, contribute significantly to stream flow. They are somehow included as part of the separated baseflow, which is likely to be overestimated from hydrograph separation. The impulse response modelling approach from the groundwater flow perspective can be an optional method to estimate the baseflow, since it considers some level of the physical connection between river and aquifer in the subsurface. Further research is however recommended to improve the simulation, such as giving more weight to wells close to the river and adding more drainage dynamics to the model input.
Highlights
IntroductionStream flow quantity and water quality are often largely influenced by groundwater via flow and solute exchange
In riverine environments, stream flow quantity and water quality are often largely influenced by groundwater via flow and solute exchange
The first step where groundwater level response is modelled shows that groundwater level in shallow aquifers reacts fast to the system input, with most of the wells reaching their peak response during the first day
Summary
Stream flow quantity and water quality are often largely influenced by groundwater via flow and solute exchange. In order to fill the research gap, we use a data-driven impulse response modelling approach to quantify the catchment scale hydrological response to meteorological forcing, and the resulting groundwater levels and baseflow, which represents the 65 river–aquifer interactions, over a 30-year period in three distinctive temperate lowland catchments. 270 (T) is the time step duration; N (unitless) is the number of time steps in the output record; βj (unitless) is an optional scaling coefficient of IRF; ψi is the error component resulting from inaccuracy in measurement, sampling intervals, or model simplification assumptions; and d0 is a hydraulic-head datum (L) for groundwater level simulation (Long, 2015) In this process, precipitation recharge (uj) is assumed to be the only forcing that can cause an increase in the hydraulic head to be above d0 (Long, 2015). The model parametrization and modifications to the original RRAWFLOW code are discussed for the two use cases in the 300 following Sect. 3.3.2 and 3.3.3
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