Baseflow Hydrograph Research Articles

Calibrated Eckhardt’s filter versus alternative baseflow separation methods: A silica-based approach in a Brazilian catchment

The Eckhardt’s filter, a recursive digital filter widely used in hydrology to separate baseflow, relies on two parameters: the recession constant (a) and the maximum allowable long-term ratio of baseflow to streamflow (BFImax). While a can be determined through regression analyses, BFImax is often assigned an arbitrary value because of limited catchment information for a more objective determination. This study aimed to assess and calibrate BFImax for a 1.2 km2 rural catchment in southern Brazil using dissolved silica data. Calibration involved minimizing differences between filter-generated baseflow hydrographs and those derived from dissolved silica measurements and mass balance across 13 monitored rainfall-runoff events. The calibrated model was compared to three established models: a modified graphical method based on local minima, a backward filter model, and a one-parameter filter. The results yielded an optimal BFImax of 0.653 with high model performance (PBias ≈ 0, NSE = 0.85, KGE = 0.74, and NRMSD = 13 %) against silica-derived baseflow. Applying the calibrated filter to a six-year streamflow dataset yielded a long-term baseflow index (BFI) value of 54 %, aligned with regional and global averages. Comparisons with other models showed that the backward filter model produced unrealistic baseflow values nearly identical to streamflow values; the local minima method overestimated baseflow by +19 % and failed to accurately represent the smoothness and peaks of the baseflow hydrographs; and the one-parameter filter represented the shape and timing of the baseflow hydrographs well, but underestimated magnitude by −19 %. These findings validate the effectiveness of the Eckhardt’s filter in generating accurate baseflow hydrographs and confirm the importance of calibrating BFImax for optimal performance. The research also endorses the use of dissolved silica measurements and the mass balance method as a reliable approach for calibrating BFImax for long-term assessment of baseflows.

Hydrometeorological field instrumentation in Lesser Himalaya to advance research for future water and food security.

Hydrometeorological monitoring and continuous data collection in ungauged mountainous regions are exciting and challenging for water resource planners compared to the measurement in plain areas. Lesser Himalayas in the mountainous areas face the insufficiency of continuous hydrometeorological data, hindering our understanding of hydrological processes and hampering integrated water resources management. This present study focuses on the setup of the field instruments for collecting hydrometeorological data and analyzing continuously collected data at Aglar watershed to assess hydrometeorological parameters' spatial and temporal distribution. The instrumentation includes monitoring one sub-surface flow, five stream flows, four rain gauges, and one automatic weather station. The relationship between the stage and the discharge was established based on the collected data for three streams. The analyzed seasonal rainfall revealed 726.7 mm of rain occurred during the monsoon with an intensity of less than 16 mm/day. The Paligaad sub-watershed displayed a flashy response towards the rainfall events, whereas the Upper Aglar exhibited a wide range of dampening runoff responses for different rainfall events. The monitored sub-surface flow varies annually, and during the monsoon season, interflow and baseflow hydrograph decayed more rapidly at the rate of 0.04 day-1 and 0.78 day-1, respectively. The installed AWS has been used to measure crop water requirements and plan for better strategies to cope with future food and water security. The high-frequency generated data will help answer the queries related to hydrological responses of different watershed characteristics.

Evaluation of baseflow separation methods with real and synthetic streamflow data from a watershed

• Performance of graphical & digital filter baseflow separation methods are compared. • Methods are compared using real data with a subjective concept of hydrologic plausibility. • Synthetic data from an integrated hydrologic model used for more rigorous assessments. • Estimated baseflow hydrographs reveal seasonal variability. • Filtered UKIH approach works best for most study locations but depends spatially. Baseflow originating primarily from groundwater is a critical streamflow component, although its accurate estimation is fraught with significant difficulties. This study estimates baseflow through existing graphical and digital filter methods, using actual streamflow data from a gauging station at the Alder Creek Watershed (ACW) and synthetic streamflow data at ten study locations within the same watershed simulated with HydroGeoSphere (HGS) (Aquanty Inc., 2018). There are four widely used graphical (Institute for Hydrology, 1980; Sloto and Crouse, 1996; Aksoy et al., 2008) and six digital filtering (Lyne and Hollick, 1979; Chapman and Maxwell, 1996; Furey and Gupta, 2001; Eckhardt, 2005; Tularam and Ilahee, 2008; Aksoy et al., 2009) baseflow separation approaches compared in this study. To determine the most optimal approach, baseflow estimates from real data are assessed based on the subjective concept of hydrologic plausibility, while baseflow estimates obtained from a HGS streamflow record with graphical and digital filtering methods are compared to those computed directly by HGS. Overall, results from this study indicate that baseflow hydrographs reveal a seasonal pattern at the ACW. During wintertime, streamflow is composed almost entirely of baseflow, whereas during summertime, baseflow only consists approximately 20% to 60% of streamflow. After comparing baseflow estimates with those computed by HGS, the most optimal approaches at the ten study locations are assessed. Results show that the best approach at six study locations is the FUKIH (Aksoy et al., 2009) approach, while at three locations, the Chapman and Maxwell (1996) approach and for one location, the Eckhardt (2005) approach performed the best. In conclusion, it is inferred that the most optimal approach within the ACW varies spatially.

Critical role of groundwater discharge in sustaining streamflow in a glaciated alpine watershed, northeastern Tibetan Plateau

As the hydrologic buffering capacity of glaciers diminishes on climate warming, groundwater stored in the glaciated alpine watersheds becomes an important source of streamflow, quantifying the groundwater contribution to this streamflow is significant for better predictions of the impact of rapidly disappearing glaciers on regional water resources. However, the role of groundwater in sustaining streams remains unclear. Here, we selected the upper Shule River Basin (USRB) on the northeast Tibetan Plateau (NETP) as a case to address this knowledge gap through a comprehensive study of geochemistry and stable isotopes data, the application of an end member mixing model and the baseflow hydrograph separation program (HYSEP). Our results indicate that even though the potential sources of streamflow exhibited distinct monthly differences during December 2012‐December 2013, the groundwater was the dominant contributor to streamflow generation in the USRB. The groundwater contributed 45% to 100% of the monthly mean streamflow, and the annual mean value of 70%. By contrast, the glacier-snow meltwater and precipitation only contributed 12% and 18% of the annual discharge. The volume contributed by groundwater was calculated as 9.93 × 108 m3, approximately six times higher than the input of the glacier-snow meltwater (i.e., 1.63 × 108 m3). From 1954 to 2018, the volume of the groundwater discharge to the streamflow in the USRB continuously increased from 4.83 × 108 m3/a (65% of total streamflow) in the 1950s to 10.34 × 108 m3/a (71% of total streamflow) in the 2010s, an increase of 2.14 times. The retreating glacier, as well as increasing precipitation and temperature, were determined to be the main reasons for the increase in groundwater discharge to the streamflow. Our findings suggest that groundwater contribution is more important than was previously thought in the glaciated alpine watersheds on the NETP.

Long-Term Modelling of an Agricultural and Urban River Catchment with SWMM Upgraded by the Evapotranspiration Model UrbanEVA

Evapotranspiration (ET) has a decisive effect on groundwater recharge and thus also affects the base flow of the receiving water. This applies above all to low-lying areas with a low depth to groundwater (GW), as is often the case in the north German lowlands. In order to analyze this relation, a coupled rainfall-runoff and hydraulic stream model was set up using the software SWMM-UrbanEVA, a version of the software SWMM that was upgraded by a detailed ET module. A corresponding model was set up for the same site but with the conventional software SWMM to compare the water balance and hydrographs. The total amount of ET calculated with the SWMM software is 7% higher than that computed with the upgraded version in the period considered. Therefore, less water is available for soil infiltration and lateral groundwater flow to the stream. This generally leads to a slight underestimation of base flows, with the exception of a notably wet summer month when the base flows were highly overestimated. Nevertheless, the base flow hydrograph shows a good adaptation to observed values (MAE = 0.014 m3s−1, R = 0.88, NSE = 0.81) but gives worse results compared to SWMM-UrbanEVA. The latter is very well able to reflect the GW-fed base flow in the sample stream in average (MAE = 0.011 m3s−1) and in its dynamics (R = 0.93, NSE = 0.85). By applying the UrbanEVA upgrade, SWMM is applicable to model the seasonal dynamics of near-natural river basins.

Isotope hydrology of a tropical coffee agroforestry watershed: Seasonal and event‐based analyses

AbstractStable isotope variations are extremely useful for flow partitioning within the hydrologic cycle but remain poorly understood throughout the tropics, particularly in watersheds with rapidly infiltrating soils, such as Andisols in Central America. This study examines the fluctuations of stable isotope ratios (δ18O and δ2H) in the hydrologic components of a tropical coffee agroforestry watershed (~1 km2) with Andisol soils in Costa Rica. Samples were collected in precipitation, groundwater, springs, and stream water over 2 years. The local meteoric water line for the study site was δ2H = 8.5 δ18O + 18.02 (r2 = 0.97, n = 198). The isotope ratios in precipitation exhibited an enriched trend during the dry season and a notable depletion at the beginning of the wet season. The δ18O compositions in groundwater (average = −6.4‰, σ = 0.7) and stream water (average = −6.7‰, σ = 0.6) were relatively stable over time, and both components exhibited more enriched values in 2013, which was the drier year. No strong correlation was observed between the isotope ratios and the precipitation amount at the event or daily time‐step, but a correlation was observed on a monthly scale. Stream water and base flow hydrograph separations based on isotope end‐member estimations showed that pre‐event water originating from base flow was prevalent. However, isotope data indicate that event water originating from springs appears to have been the primary driver of initial rises in stream flow and peak flows. These results indicate that isotope sampling improves the understanding of water balance components, even in a tropical humid location, where significant variations in rainfall challenge current modelling efforts. Further research using fine‐scale hydrometric and isotopic data would enhance understanding the processes driving spring flow generation in watersheds.

Estimating Groundwater Recharge in the Semiarid Al-Khazir Gomal Basin, North Iraq

The mean annual recharge of Al-Khazir Gomal Basin was estimated as a basis for decision makers regarding the renewability and sustainability of groundwater. For this purpose, two approaches were used: hydrograph analysis and water table fluctuation (WTF). The long-term mean daily stream-flow records of Al-Khazir River (1969–1981) were used to estimate groundwater discharge by base-flow hydrograph separation and displacement recession curve methods. Four base-flow separation methods were used; one is the graphical separation method, and three are automated separation methods included in the web-based Hydrograph Analysis Tool. The annual recharge estimated by WTF was 111.6 mm/y, and the average annual recharge estimated by the four base-flow separation methods was 125.8 mm/y. Estimating recharge by the water table fluctuation method does not incorporate spatial variability contained in the whole watershed, because the specific yield did not represent the entire basin. However, the hydrograph analysis method can give a comprehensive estimation of the net integrated recharge for the entire watershed, which includes different recharge mechanisms. The displacement recession curve method deviates a lot (>30 mm/y) from the other methods, which indicates that this method may not be suitable to apply in such large watersheds.

Performance assessment and improvement of recursive digital baseflow filters for catchments with different physical characteristics and hydrological inputs

Recursive digital filters (RDFs) are one of the most commonly used methods of baseflow separation. However, how accurately they estimate baseflow and how to select appropriate values of filter parameters is generally unknown. In this paper, the output of fully integrated surface water/groundwater (SW/GW) models is used to obtain optimal parameters for, and assess the accuracy of, three commonly used RDFs under a range of physical catchment characteristics and hydrological inputs. The results indicate that the Lyne and Hollick (LH) filter performs better than the Boughton and Eckhardt filters, over a larger range of conditions. In addition, the optimal values of the filter parameters vary considerably for all three filters, depending on catchment characteristics and hydrological inputs. The dataset of the 66 catchment characteristics and hydrological inputs, as well as the corresponding simulated total streamflow and baseflow hydrographs obtained using the SW/GW model, can be downloaded as Supplementary material.

Effects of Linking a Soil‐Water‐Balance Model with a Groundwater‐Flow Model

A previously published regional groundwater-flow model in north-central Nebraska was sequentially linked with the recently developed soil-water-balance (SWB) model to analyze effects to groundwater-flow model parameters and calibration results. The linked models provided a more detailed spatial and temporal distribution of simulated recharge based on hydrologic processes, improvement of simulated groundwater-level changes and base flows at specific sites in agricultural areas, and a physically based assessment of the relative magnitude of recharge for grassland, nonirrigated cropland, and irrigated cropland areas. Root-mean-squared (RMS) differences between the simulated and estimated or measured target values for the previously published model and linked models were relatively similar and did not improve for all types of calibration targets. However, without any adjustment to the SWB-generated recharge, the RMS difference between simulated and estimated base-flow target values for the groundwater-flow model was slightly smaller than for the previously published model, possibly indicating that the volume of recharge simulated by the SWB code was closer to actual hydrogeologic conditions than the previously published model provided. Groundwater-level and base-flow hydrographs showed that temporal patterns of simulated groundwater levels and base flows were more accurate for the linked models than for the previously published model at several sites, particularly in agricultural areas.

Baseflow separation in a small watershed in New Brunswick, Canada, using a recursive digital filter calibrated with the conductivity mass balance method

AbstractBaseflow separation is important for obtaining critical parameters for hydrological models. As measuring the baseflow component directly is difficult, various analytical and empirical baseflow separation methods have been developed and tested. The recursive digital filter (RDF) method is commonly used for baseflow separation due to its simplicity and low data requirement. However, parameters used in the RDF method are often determined arbitrarily, resulting in high uncertainty of the estimated baseflow rate. A more accurate method is the conductivity mass balance (CMB) method, which is established based on the differences in physical processes between baseflow and surface runoff. In this research, the output of the CMB method was used to calibrate the parameters of an RDF model, and the calibrated RDF model was used to estimate monthly, seasonal and annual baseflow rate and baseflow index for the past 19 years using streamflow discharge records. The characteristics of the baseflow hydrographs were found to be consistent with the hydrological and hydrogeological conditions of the research area. Research results indicated that the accuracy of the RDF model has been greatly enhanced after being calibrated with the CMB method so that the RDF model can provide more reliable baseflow separation results for a long‐term study. Copyright © 2012 John Wiley & Sons, Ltd.

Analysis of groundwater regime on the basis of stream flow hydrograph

During the drought the flow in streams is reduced and is dominated by base flow. Baseflows are characteristic of low flow periods and provide information on available water resources in the basin during the drought, particularly on the aquifer and retention basin characteristics. This paper deals with the possibility of analysis and simulation of baseflow, and the determination of the pattern of its changes based on the total registered streamflow hydrograph at the catchment outlet. The basis for modeling the base flow changes in the time were base flow values obtained from the streamflow hydrograph by application of the graphical local minimum method. Applying the simulation model developed in this study, simulations of base flow hydrographs were performed for three characteristic years (1970, 1985, and 1990). It was shown that discrepancies between values of the base flows obtained through application of the local minimum method and the model are within the limits of tolerance.

Groundwater Recharge through Conservation Structures – A Study in Ghat Area of Orissa

Groundwater recharge from two different water conservation structures under humid conditions of eastern ghat high land (EGHL) zone of Orissa were estimated by employing water table fluctuation procedure. A power function relationship best fitted the recharge and water storage depths. Contribution of base flow was segregated from the recharge values using base flow hydrograph separation technique. Potential groundwater recharge based on four years (2004-07) was estimated in the range between 3.5 - 11.0 % of the annual rainfall while considering the runoff contributing area of the conservation structures. Temporal groundwater contour maps generated using grid based graphics SURFER package (Version # 8) and GPSMAP (Version # 76CSX) for the study watershed revealed that there was a total net increase of 8.12 m and decrease of 2.61 m water table depths during wet and dry periods, respectively, resulting in net increase of water table by 1.38 m per year due to the influence of the water conservation structures. Groundwater quality of the wells in the watershed was found to be safe for irrigation and domestic consumption purposes.

Estimation of aquifer lower layer hydraulic conductivity values through base flow hydrograph rising limb analysis

The estimation of catchment‐averaged aquifer hydraulic conductivity values is usually performed through a base flow recession analysis. Relationships between the first time derivatives of the base flow and the base flow values themselves, derived for small and large values of time, are used for this purpose. However, in the derivation of the short‐time equations, an initially fully saturated aquifer without recharge with sudden drawdown is assumed, which occurs very rarely in reality. It is demonstrated that this approach leads to a nonnegligible error in the parameter estimates. A new relationship is derived, valid for the rising limb of a base flow hydrograph, succeeding a long rainless period. Application of this equation leads to accurate estimates of the aquifer lower layer saturated hydraulic conductivity. Further, it has been shown analytically that, if base flow is modeled using the linearized Boussinesq equation, the base flow depends on the effective aquifer depth and the ratio of the saturated hydraulic conductivity to the drainable porosity, not on these three parameters separately. The results of the new short‐time expression are consistent with this finding, as opposed to the use of a traditional base flow recession analysis. When base flow is modeled using the nonlinear Boussinesq equation, the new expression can be used, without a second equation for large values of time, to estimate the aquifer lower layer hydraulic conductivity. Overall, the results in this paper suggest that the new methodology outperforms a traditional recession analysis for the estimation of catchment‐averaged aquifer hydraulic conductivities.

Generation of Total Runoff Hydrographs Using a Method Derived from a Digital Filter Algorithm

A reliable prediction of the total runoff hydrograph is necessary for water resources management. This study investigates two approaches to generate total runoff hydrograph by adding baseflow to direct runoff hydrographs. The first approach uses a method, derived from a digital filter algorithm for hydrograph separation, to generate baseflow hydrographs from direct runoff hydrographs. The method appears to perform well in producing the overall shape of the total runoff hydrographs and the acceptable mass balance errors for a year of water cycle. For application, the recession baseflow constant needs to be estimated reliably and the initial baseflow could be approximated to the long-term mean dry weather flow. The second approach assumes a constant baseflow rate. Although this approach is still capable of producing the overall hydrograph shape, it yields high mass balance errors in the total runoff hydrographs for both monthly and long-term periods. Further analysis shows that two-third of the mass balance...

A new baseflow separation method based on analytical solutions of the Horton infiltration capacity curve

AbstractThe 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.

Functional intercomparison of hillslopes and small catchments by examining water source, flowpath and mean residence time

Intercomparisons of hillslopes and catchments in different hydrogeomorphic settings are rare. Those comparison studies that have been completed have focused largely on bulk outflow and chemistry. Here, we present a new functional intercomparison of two well studied hillslopes: one in New Zealand at Maimai and one in Japan at Fudoji. Slope angle, slope length, soil depth, climate and vegetation of both hillslopes are very similar. Thus, questions posed include: In what ways are the hillslopes similar or different as expressed via the combination of throughflow rate, tensiometric response, event/pre-event water partitioning, quickflow rates and mean residence time? How does the apparent difference in soil drainable porosity affect the hillslope response to storm rainfall? How do the apparent differences in bedrock permeability affect the residence time of water at the slope base and catchment outlet? Our results suggest that in steep, wet and thin soil hillslopes, bedrock permeability and water retention characteristics combine to form a first order (main or dominant) control on the baseflow hydrograph and its mean residence time. For storm rainfall totals above about 50 mm, soil drainable porosity appears to be a first order control on the extension of upslope subsurface saturated area and the event water ratio of hillslope discharge in steep, wet and thin soil hillslopes. Although this functional intercomparison is a posteriori, it has yielded information that was not possible from the individual hillslope studies upon which it is based. In particular, it has informed a new, more generalizable, conceptualization of subsurface flow for steep wet hillslopes. We argue that intercomparison of other such hillslopes and small catchments may be a pathway forward for defining first order controls of complex hillslope hydrologic dynamics.

Baseflow separation based on analytical solutions of the Boussinesq equation

A technique for baseflow separation is presented based on similarity solutions of the Boussinesq equation. The method makes use of the simplifying assumptions that a horizontal impermeable layer underlies a Dupuit aquifer which is drained by a fully penetrating stream. The value of the baseflow maximum as well as the baseflow recession hydrograph can be estimated by fitting the analytical solutions of the Boussinesq equation to the observed discharge values for individual flood events. For the rising limb of the baseflow hydrograph a linear function is assumed for simplicity. The method is first demonstrated on three watersheds for a total of five flood events and extensively applied over a three year period for the Mahantango Creek, Pennsylvania watershed. The proposed method reduces some of the subjective aspects long associated with baseflow separation techniques.

The unit hydrograph model for hydrograph separation

Procedures are presented for baseflow separation based on the unit hydrograph theory. When a mathematical model is used to represent the baseflow unit hydrograph, the parameters derived from a recession limb of the baseflow hydrograph can be further used to determine the rising limb of the baseflow hydrograph. The simple procedures involve estimation of the two parameters of the model using discharge data with simple equations. Once parameters have been estimated, the mathematical model for an entire baseflow hydrograph can be used to determine both the temporal processes and total quantity of a baseflow hydrograph. Using this method the separated component of baseflow during study periods is about 63% of the total storm runoff from two small rural catchments in Australia.

Three‐Dimensional, Transient, Saturated‐Unsaturated Flow in a Groundwater Basin

A three‐dimensional finite difference model has been developed for the treatment of saturated‐unsaturated transient flow in small nonhomogeneous, anisotropic geologic basins. The uniqueness of the model lies in its inclusion of the unsaturated zone in a basin wide model that can also handle both confined and unconfined saturated aquifers, under both natural and developed conditions. The integrated equation of flow is solved by the line successive overrelaxation technique. The model allows any generalized region shape and any configuration of time variant boundary conditions. When applied to natural flow systems, the model provides quantitative hydrographs of surface infiltration, groundwater recharge, water table depth, and stream base flow. Results of simulations for hypothetical basins provide insight into the mechanisms involved in the development of perched water tables. The unsaturated basin response is identified as the controlling factor in determining the nature of the base flow hydrograph. Application of the model to developed basins allows one to simulate not only the manner in which groundwater withdrawals are transmitted through the aquifers, but also the changes in the rates of groundwater recharge and discharge induced by the withdrawals. For any proposed pumping pattern, it is possible to predict the maximum basin yield that can be sustained by a flow system in equilibrium with the recharge‐discharge characteristics of the basin.

Theoretical Baseflow Curves

Baseflow curves are obtained by solving a nonlinear partial differential equation of groundwater flow for different boundary conditions. A theoretical basis is provided for differentiating between these curves for shallow and deep aquifers. Various linearized solutions and their limitations and errors are elucidated. Mathematical expressions are derived for the effects of evapotranspiration and leakage loss in substantially reducing the baseflow and rendering the stream influent or dry. Upward leakage from an underlying artesian aquifer casuses the baseflow to be more sustained and reduces its recession rate. Aquifer recharge of duration T , simulated by a sine function, leads to a baseflow hydrograph which peaks at 0.75 T and becomes parallel to the no-recharge curve after about 1.5 T .