Lag in Hydrologic Recovery Following Extreme Meteorological Drought Events: Implications for Ecological Water Requirements

Hydrological regimes, being strongly impacted by climate change, play a vital role in maintaining the integrity of aquatic river habitats. We investigated lag in hydrologic recovery following extreme meteorological drought events, and we also discussed its implications in the assessment of ecological environment flow. We used monthly anomalies of three specific hydrometeorological variables (precipitation, streamflow, and baseflow) to identify drought, while we used the Chapman–Maxwell method (the CM filter) with recession constant calculated from Automatic Baseflow Identification Technique (ABIT) to separate baseflow. Results showed that: (i) Compared to the default recession parameter (α = 0.925), the CM filter with the ABIT estimate (α = 0.984) separated baseflow more accurately. (ii) Hydrological drought, resulting from meteorological drought, reflected the duration and intensity of meteorological drought; namely, longer meteorological drought periods resulted in longer hydrological drought periods. Interestingly, the time lag in streamflow and baseflow indicated that aquatic ecosystem habitat recovery also lagged behind meteorological drought. (iii) Assessing environmental flow by quantifying drought provided greater detail on hydrological regimes compared to abrupt changes, such as the increased hydrological periods and the different environment flows obtained. Taken together, our results indicated that the hydrological response in streamflow and baseflow (e.g., the time lag and the precipitation recovery rate (Pr)) played a vital role in the assessment of environmental flow.

Applicability Assessment of Estimation Methods for Baseflow Recession Constants in Small Forest Catchments

In South Korea, since small forest catchments are located upstream of most river basins, the baseflow from these catchments is important for a clean water supply to downstream areas. Baseflow recession analysis is widely recognized as a valuable tool for estimating the baseflow component of the stream hydrograph. However, few studies have applied this tool to small forest catchments. So, this study was conducted to assess the applicability of the recession analysis methods proposed in previous studies. The data used were long-term rainfall-runoff data from 1982 to 2011 in the Gwangneung coniferous (GC) and deciduous (GD) forest catchment in Gyeonggi-do, South Korea. For the applicability assessment, six recession constant estimation methods, which were used by previous studies, were selected. The recession constants of the GC and GD catchments were calculated, and applicability assessments were conducted by comparing the recession predictions and baseflow separations. As a result, the recession constants for GC and GD were 0.8480 and 0.9235, respectively. This clear difference may be due to the different forest cover in each area. The correlation regression line, AR(1) model, and the Vogel and Kroll method showed lower error rates and appropriate baseflow indexes compared with other methods.

Analysis of Flood Hydrographs in Order to Predict the Shape of Their Falling Limbs

This paper presents preliminary analyses carried out in order to assess the possibility to treat a small simple catchment as linear reservoir when modeling the runoff from a precipitation event. This analysis was carried out for the catchment of Černá Desná stream to the profile Jezdecká. The applicability of linear reservoir concept was tested by calculating the recession constant values for hydrographs falling limbs which were then evaluated in a statistical way. Specifically, five events were selected for the detail analysis. The results indicate that the linear reservoir concept can be applied in this case to predict relatively well the discharges in next 48 h. However, the results also show that there are limitations in the application of linear concept and that the introduction of non-linear reservoir could improve the prediction results.

KARAKTERISASI AKUIFER KARST MATAAIR NGELENG DENGAN PENDEKATAN VARIASI TEMPORAL SIFAT ALIRAN DAN HIDROGEOKIMIA

Flow properties and hydrogeochemistry is the main approach in this study. The purpose of thisstudy was to determine the temporal variation of the Ngeleng Spring karst aquifer flow properties,examines the temporal variation of Ngeleng Spring karst aquifers hydrogeochemistry, and to studythe relationship between the flow properties and hydrogeochemistry of Ngeleng Spring. Researchmethod in this study classified as a field survey using data such as water level, discharge, and waterchemical contents. Sampling was divided into long-term sampling and flood event sampling. Theanalysis that used in this study is a graphical analysis, scatter plot analysis, and descriptiveanalysis. The results of recession constant analysis stated that the flow component of Ngelengsprings dominated by diffuse component. Determination between flow properties andhydrogeochemistry states that on rainy season occured rain water mixing process, then on dryseason occur the domination of water interaction with the aquifer material, as well as the diffusiontransfer process because of the spring open system. Calcite aggressivity on rainy season are tendsto the unsaturated phase, while in the dry season tends to the equilibrium phase.

THE DISTRIBUTION OF FLOOD HYDROGRAPH RECESSION CONSTANT FOR CHARACTERIZATION OF KARST SPRING AND UNDERGROUND RIVER FLOW COMPONENTS RELEASING WITHIN GUNUNG SEWU KARST REGION

TThis research is carried out within two caves with underground river and one karst spring, which is locatedin Gunung Sewu karst area, Gunung Kidul. The objective of this research is to recognize some flood hydrograph properties of karst aquifer characterization in order to compare the comportment of aquifer to release its flow components between underground river and karst spring. Water level data loggers are installed within two caves and one karst spring represent upper, middle, and lower elevation of karst topography, which are Beton, Seropan, and Toto Cave, respectively. In addition, time series discharge measurement in correspond to minimum, average, and maximum flow events is conducted to formulate the Annual Stage Discharge Rating Curve. Thereby, the full year river hydrograph may be defined.Afterwards, by selecting several flood hydrograph events, the recession constant in each cave includingdiffuse flow (Kb), fissure flow (Ki), and conduit flow (Kc) recession constant, is then calculated andcompared in every location. The result shows that Beton Spring that represents the upper part of researcharea confirms the quickest respond towards rainfall events. Also, this point specifies the medium numberof diffuse recession constant (Kb=0.983), compared to Seropan (0.996), and Toto (0.937), means that theaquifer surrounding Toto Cave release its groundwater storage faster than Beton Spring and SeropanCave. On the contrary, Seropan Cave performs the highest value of diffuse recession constant (0.996) andthis situation is confirmed by its dry season discharge that still above 810 lt/second

KAJIAN KEBERLANJUTAN ALIRAN DASAR SUNGAI MELALUI ANALISIS KURVA RESESI HIDROGRAF PADA DAS KEDUANG KABUPATEN WONOGIRI PROVINSI JAWA TENGAH

The streamflow hydrograph recession curve notes that behavior of the relationship between the aquifer structure and dependencies with the groundwater outflow towards river basin channel. The recession behavior of river basin hydrographs will investigate to understand the hydrology processes of the river basin in the future. This research was conducted with the aim: to analyze the characteristics of the baseflow recession based on the parameters and coefficients of the recession, and the shape of the individual recession curve and the master recession curves both manually and through the processing of genetic algorithms using a linear reservoir model of hydrooffice software package recession curve (RC) 4.0. The results of the visualization of the recession curve shape of the watershed of the research shows there is a very interesting trend in the watershed storage process.The characteristics of the baseflow recession to research watershed with the recession curve slope describe the baseflow recession conditions, especially excellent water storage. The river basin of Keduang have the form of a relatively sloping recession curves, both individual and master recession curve with relatively high recession constant ranged between 0,80 – 0,90 have baseflow recession characteristic is excellent, i.e. the watershed water storage which is the higher volume of water storage.