Baseflow Separation Analysis Research Articles

Spatial and temporal hydrochemistry variations of karst water in Gunung Sewu, Java, Indonesia

A hydrogeochemical study was conducted in the Gunung Sewu Karst, Java Island, Indonesia. The main objective of this study is to describe the spatial and temporal variations of hydrochemistry that occur in the central and western parts of Gunung Sewu. Discharge measurements for a one-year period are taken in some karst springs or underground rivers to define their discharge hydrograph. Furthermore, baseflow separation analysis was conducted to determine the base flow percentage throughout the year. Water sampling for hydrogeochemical analysis was taken every month to represent the dry and rainy season conditions. To describe the hydrogeochemical processes, a scatter plot analysis with a small sample size was conducted. The results showed that the hydrochemistry of karst water in the study area has different characteristics spatially and temporally. Within the dry season, the dominant hydrogeochemical process is water–rock interaction (precipitation of calcite mineral), indicated by achieving the maximum level of Ca2+, HCO3 −, electrical conductivity, base flow percentage, and SI calcite, with the lowest level of log $$P_{{{\text{CO}}_{2} }}$$ in the water. In addition, the dry season hydrochemistry is characterized by a strong relationship between electrical conductivity–calcium/bicarbonate, base flow percentage-discharge, base flow percentage-SI calcite, and SI calcite-log $$P_{{{\text{CO}}_{2} }}$$ . Spatially, the different level of correlations between these parameters depended on the sampling location, flow recharge, and the conduit development. Conversely, in the rainy season, the hydrogeochemical process shifted from water–rock interaction to dilution of rainwater as a result of rain water supply through a conduit system channel, which is characterized by declining Ca2+, HCO3 −, electrical conductivity, base flow percentage, and SI calcite, with the highest level of log $$P_{{{\text{CO}}_{2} }}$$ in the water. The dilution of rainwater process also caused a decline in the correlation of some hydrogeochemical parameters.

Diffuse flow characteristics and their relation to hydrochemistry conditions in the Petoyan Spring, Gunungsewu Karst, Java, Indonesia

This study was conducted on the Petoyan Spring, one of the most important springs in the western part of Gunung Sewu Karst, Java, Indonesia. The main purpose of the study is to define the diffuse flow characteristics of the spring. It also focuses on identifying the relationship between the diffuse flow proportion and several hydrochemical parameters to provide a better aquifer characterization. Water-level monitoring and discharge measurements were conducted over an eight months period in order to define the discharge hydrograph. The calculation of recession constants, including the diffuse flow (Kb), fissure flow (Ki), and conduit flow (Kc), was done by selecting several flood hydrograph events. Furthermore, the base flow-separation analysis was conducted to determine the diffuse flow proportion throughout the research period. Water sampling for hydrogeochemical analysis was taken every week and every hour for two selected flood events. A bivariate plot analysis between the diffuse flow proportion and certain hydrochemical parameters was made in order to describe the hydrogeochemical processes. The results showed that the diffuse- flow significantly dominates the spring discharge during non-flooding and flooding recession periods. Conversely, during the rising limb period, the diffuse proportion decreased drastically due to the conduit flow supply. This fact was also supported by the high Kb and short Tp (time to peak) and Tb (time to base flow) values. Hydrogeochemically the correlation between the diffuse flow proportion and major dissolved elements during the flood recession periods was strong because the conduit flow domination was replaced by the diffuse flow, causing the domination of water-rock interaction. According to the diffuse flow and its relation to its hydrochemistry, it is apparent that small fractures in the Petoyan Spring aquifer still provide good storage for the diffuse flow, even though the conduit fracture has already been developed.

Wet season hydrochemistry of Bribin Cave in Gunung Sewu Karst, Indonesia

This research was conducted on the Bribin River, the most important underground river in the Gunung Sewu Karst, Gunung Kidul, Java, Indonesia. The main purpose of this study was to define the wet-season hydrochemistry of this river. This research also focuses on identifying the relationship between hydrochemical parameters to provide better aquifer characterization. Water-level monitoring and discharge measurements were conducted over a 1-year period to define the discharge hydrograph. Furthermore, baseflow-separation analysis is conducted to determine the diffuse-flow percentage throughout the year. Water sampling for hydrogeochemical analysis is taken every month in the wet season and every 2 hours for two selected flood events. To describe the hydrogeochemical processes, a bivariate plot analysis of certain hydrochemical parameters is conducted. The results show that the diffuse-flow percentage significantly controls the river hydrochemistry. The domination of diffuse flow occurs during non-flooding and flood recession periods, which are typified by a high value of calcium and bicarbonate and low CO2 gas content in water. Conversely, the hydrochemistry of flood events is characterized by the domination of conduit flow and CO2 gas with low calcium and bicarbonate content. According to the wet-season hydrochemistry, it seems that the small- and medium-sized fractures in the Bribin aquifer still provide storage for the diffuse and fissure flows, although the conduit fracture is already developed.

Contributions of DOC from surface and groundflow into Lake Võrtsjärv (Estonia)

Hydrological changes have the greatest impact on shallow lakes where they alter the water volume and lake depth noticeably. Dissolved organic carbon (DOC), which is markedly affected by hydrological factors, has an important role in many biogeochemical processes. The DOC load supplied to Lake Vortsjarv, the second largest lake in Estonia, was studied on the scale of the subcatchments discharging into the lake. Daily discharges and biweekly or monthly DOC concentrations were measured close to the river outlets over the years 1990–2002. The stream flow data were separated into groundflow and surface flow by applying local minimum and recursive digital filtering methods. Constituent load estimation software, LOADEST, was used to estimate DOC concentrations and load. LOADEST performed well for three of the four rivers. The total estimated DOC load to Vortsjarv from all four main rivers varied from 1,320 to 4,934 t year−1. The average annual load over the 13-year period was 3,265 t year−1 or 1.18 g C m−2 year−1. Baseflow separation analysis indicated that the DOC load originating from groundflow contributed 79% and 69% of the total load according to the digital filter and local minimum methods, respectively. The results of our study demonstrate the utility of linking the rating-curve method and baseflow separation to assess the allochthonous DOC load to Vortsjarv both currently and under changing climatic conditions.