Exploring river–aquifer interactions and hydrological system response using baseflow separation, impulse response modelling and time series analysis in three temperate lowland catchments
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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.Keywords:
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The results of a hydrograph study for small and medium Pennsylvania watersheds is presented. Twenty-six Pennsylvania watersheds, ranging in size from 2.4 sq miles to 210 sq miles, were analyzed. Interflow is separated from surface runoff and procedures are described to develop both. For surface runoff, readily obtainable watershed characteristics are correlated with parameters of a mathematical model for the unit hydrograph. Interflow is correlated with rainfall, runoff, and antecedent moisture conditions. A complete procedure for design hydrographs for small ungaged watersheds in Pennsylvania is presented.
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More severe and frequent flood and drought have increased the attentions on the river management. In particular, baseflow is an important element among many streamflow characteristics because streamflow is mainly consisted of direct runoff and baseflow. In this regard, this study attempted to analyze the relationship between streamflow variability and baseflow contributions on Nakdong river basin. For this, two Streamflow Variability Indices (SVI) were used: Coefficient of Variation (CV) and Coefficient of Flow Regime (CFR). Furthermore, baselow separation was individually conducted by three methods (PART, WHAT and BFLOW), and based on this, Baseflow Index (BFI) was calculated. Also, we used the daily streamflow data retrieved from 27 gauge stations in Nakdong river basin for baseflow separation. The results showed that BFI calculated by three models ranges from 0.14 to 0.90 for 27 gauge stations. For SVI, BFI has much higher correlation with CV than with CFR. Also, the inversely proportional relationship between BFI and CV showed that higher baseflow contribution, less streamflow variability.
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Abstract The separation of baseflow is an important issue in hydrology. The objective of this paper is to develop a new baseflow separation method based on the Horton infiltration capacity curve. For this purpose, the mathematical expressions of three parameters for the Horton infiltration capacity curve were derived in terms of rainfall and runoff data, and the lag time of the effective rainfall in the unsaturated zone and the groundwater flow routing equation are also presented. With these equations, the baseflow hydrographs at the outlet of the basin can be separated. The flow chart of the proposed method for baseflow hydrograph separation is given. Three recent baseflow separation methods, i.e. digital filter, non‐linear reservoir and the Boussinesq equation, were chosen as parallel schemes to compare with the proposed method. Rainfall‐runoff data from four watersheds located in different climatic regions in China were selected and used as case studies. Test and application results indicate that the proposed baseflow hydrograph separation method is in accordance with the hydrological physical process. The proposed method is comparable with current available methods and reduces some of the subjective aspects for the rising limb of the baseflow hydrograph, and it is useful for unit hydrograph analysis and for the study of the rainfall‐runoff relationship. Copyright © 2006 John Wiley & Sons, Ltd.
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Baseflow separation from rainfall and streamflow data is a fundamental problem in applied hydrology, unsolved despite extensive investigations. For example, a part of baseflow is interflow, which results from rainfall infiltration, but almost all of the existing baseflow separation methods, such as graphic and filter methods, have nothing to do with it, which is a serious flaw from the viewpoint of science. The objective of this research is thus to present an innovative baseflow separation method based on the recent general unit hydrograph (UH) model and the classic Green-Ampt infiltration equation. Specifically, we divided a rainfall hyetograph into two parts using the Green-Ampt infiltration equation: one for surface flow that generates direct runoff and the other for subsurface flow that recharges groundwater and generates interflow. As with direct runoff from the surface system, we approximated the subsurface system as a linear system and thus applied the general UH model for interflow in the unsaturated soil zone, where excess infiltration is defined by analogy to excess rainfall. We assumed that groundwater flow could be described by the classic recession curve; we then added interflow and the groundwater flow to obtain the baseflow. We validated the proposed method with six real-world case studies representing four interflow patterns. Particularly, we found that, unlike direct runoff, the interflow UH model parameters are not unique, depending on stream stages. This implies that the subsurface system is a time-variant linear system, which can even make a negative interflow if groundwater is recharged from streams. We expect that this research will provide a better baseflow separation method and thus improve our understanding of watershed processes.
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The most common way of reducing non-point source pollutants from agricultural areas is the installation of reservoirs. However, this method is only effective for surface runoff of settleable pollutants. This study was conducted to estimate the effect of interflow, baseflow, and surface runoff on pollutant runoff in a small agricultural catchment. Runoff of organic matters, SS, and T-P were directly proportional to the rainfall variation, while ammonia and nitrate were inversely proportional to the amount of rainfall. The interflow and baseflow was only 46% of the total stream flow, but the nitrate load reached 78%. The interflow as a nutrient transport pathway should be considered for managing a stream water quality. It requires careful attention and appropriate control methodology such as vegetation to consider the influence by interflow. The reservoir as a dry extended detention pond (DEDP) has function of nutrient captor.
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More severe and frequent flood and drought have increased the attentions on the river management. In particular, baseflow is an important element among many streamflow characteristics because streamflow is mainly consisted of direct runoff and baseflow. In this regard, this study attempted to analyze the relationship between streamflow variability and baseflow contributions on Nakdong river basin. For this, two Streamflow Variability Indices (SVI) were used: Coefficient of Variation (CV) and Coefficient of Flow Regime (CFR). Furthermore, baselow separation was individually conducted by three methods (PART, WHAT and BFLOW), and based on this, Baseflow Index (BFI) was calculated. Also, we used the daily streamflow data retrieved from 27 gauge stations in Nakdong river basin for baseflow separation. The results showed that BFI calculated by three models ranges from 0.14 to 0.90 for 27 gauge stations. For SVI, BFI has much higher correlation with CV than with CFR. Also, the inversely proportional relationship between BFI and CV showed that higher baseflow contribution, less streamflow variability.
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Flood forecasting
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