Hydrologic Flow Models Research Articles

Complex Effects of Tides on Coastal Groundwater Revealed by High‐Resolution Integrated Flow Modeling

AbstractRiver deltas typically have high population density and support a wide range of intensive and prosperous socioeconomic activities. The hydrological processes in these regions are complex, primarily due to the interactions among the river, aquifer, and sea. However, a systematic and quantitative elaboration of the river‐aquifer‐sea interactions is still lacking. Here, we developed an integrated hydrological flow model for the Pearl River Delta (PRD), which contains the world's largest urban area in both size and population, to gain a deeper understanding of the complexities in the river‐aquifer‐sea interactions. The model performance was validated and cross‐checked via observations at gauging stations and independent remote‐sensing products (e.g., soil moisture, evapotranspiration, and total water storage anomalies). Based on the 10‐year simulation results (2004–2013), the major findings of this study are as follows: (a) accurate representation of the tidal effect is important not only for simulating short‐term flow dynamics but also for capturing the characteristics of long‐term hydrological fluxes and states; (b) the flow‐model‐computed average groundwater discharge rate per unit length of the coastline for the PRD is 3.01 m3/d/m, which is comparable with those derived from water budget approaches but 1–2 orders of magnitude lower than the total submarine groundwater discharge (SGD) estimated by using isotope tracer‐based methods; (c) the temporal variation of SGD is controlled by tidal forcing on an hourly time scale, but by terrestrial hydrological processes on monthly and annual time scales; and (d) an integrated hydrological flow model can be used to identify distinct and large subsurface zones sensitive to tidal fluctuations, quantifying the pivotal role of ocean tides in shaping the coastal groundwater system. This study represents a first step in using an integrated hydrological model to explore river‐aquifer‐sea interactions and their effects on the regional groundwater system simultaneously driven by meteorological and tidal forcings.

Quantifying basin-scale changes in groundwater storage using GRACE and one-way coupled hydrological and groundwater flow model in the data-scarce Bandung groundwater Basin, Indonesia

Assessing basin-scale groundwater storage changes is often difficult when groundwater table data are scarce. In this study, we quantify the groundwater storage changes by using the Wflow_sbm hydrological model coupled with the MODLOW groundwater model in the data-scarce area of the Bandung groundwater basin, Indonesia. The soil moisture storage change calculated by Wflow_sbm plus the groundwater storage change calculated by MODFLOW is compared to the water storage change estimated by the GRACE satellite between 2005 and 2015. The calculated cross-correlation coefficient is 0.502, and 62.1% of the simulated water storage change falls within GRACE's estimated uncertainty bounds. The important context in the water storage comparison are GRACE temporally local time-lags, data gaps in GRACE datasets, and differences in model seasonal performance and analyzed domain characteristics. The two latter factors highlight the importance of considering local groundwater-related information over large-scale global datasets in basin-scale groundwater storage change assessment. Based on the groundwater flow model, the current predicament of groundwater abstraction in the Bandung groundwater basin is highly unsustainable for future groundwater uses. On average, the groundwater storage in the study area is dwindling at the rate of 87 million m3/year between 2005 and 2018, dominantly a consequence of groundwater abstraction, whose effect is rippled to further impact the whole groundwater flow regime. Agreed by the situation shown by the limited data, the simulated groundwater table drawdown, spatially, is found to be locally and non-uniformly distributed. The capability of a one-way coupled hydrological and groundwater model to investigate basin-scale groundwater storage change, with comparable estimates to the GRACE dataset, unravel the opportunity of using such methods to estimate the behavior of future groundwater storage dynamics under the changing anthropogenic and climatic factors in catchment-scale studies.

Depth estimates of anomalous subsurface sources using 2D/3D modeling of potential field data: implications for groundwater dynamics in the Ziway-Shala Lakes Basin, Central Main Ethiopian Rift

Quantitative analysis of potential field data are made in the Ziway-Shala lakes basin over an area bounded by 38°00′ E - 39°30′ E and 7°00′ N - 8°30’ N. Most previous geophysical studies in the region under consideration focus on mapping the deep crustal structures and undulation of the Moho depth. Only few studies are targeted at mapping the shallow subsurface structures. The main focus of this paper is mapping geometries of the major lithological and structural units of the shallow subsurface using gravity and magnetic data. The ultimate objective of the research is to understand the hydrogeological dynamics of the region through mapping interfaces geometries. Automatic inversions, 2D joint forward modeling and 3D inversion are the major techniques employed. The 2D Werner de-convolution based on both gravity and magnetic data along the rift axis showed source depths tending to deepen northwards. Source depths estimates determined by Source Parameter Imaging also showed similar tendency. This is further strengthened by the joint 2D forward modeling of gravity and magnetic data which showed the top of the basement is sloping northwards. The result of the 3D gravity interface inversion agrees with results of the above mentioned depth estimation techniques. Finally, the gravity power spectral analysis resulted in two depth estimates, 1.53 km and 2.87 km which approximate the positions of two density interfaces. The shallow depth interface is thought to presumably delineate the low density Fluvio-lacustrine sediments including the rift floor volcanic units and crystalline basement. Our investigation results agree with the results of previous seismic studies which identified low velocity (“sediment-volcanic”) horizon in the rift floor with low resolution. The information obtained with regard to water balance of the basin, salinity level of the lakes and the conceptual hydrological flow model appears to reveal that the groundwater flow in the study region is controlled by subsurface structures, particularly, the mapped interface topographies.

Modeling Streamflow and Sediment Loads with a Photogrammetrically Derived UAS Digital Terrain Model: Empirical Evaluation from a Fluvial Aggregate Excavation Operation

Soil erosion monitoring is a pivotal exercise at macro through micro landscape levels, which directly informs environmental management at diverse spatial and temporal scales. The monitoring of soil erosion can be an arduous task when completed through ground-based surveys and there are uncertainties associated with the use of large-scale medium resolution image-based digital elevation models for estimating erosion rates. LiDAR derived elevation models have proven effective in modeling erosion, but such data proves costly to obtain, process, and analyze. The proliferation of images and other geospatial datasets generated by unmanned aerial systems (UAS) is increasingly able to reveal additional nuances that traditional geospatial datasets were not able to obtain due to the former’s higher spatial resolution. This study evaluated the efficacy of a UAS derived digital terrain model (DTM) to estimate surface flow and sediment loading in a fluvial aggregate excavation operation in Waukesha County, Wisconsin. A nested scale distributed hydrologic flow and sediment loading model was constructed for the UAS point cloud derived DTM. To evaluate the effectiveness of flow and sediment loading generated by the UAS point cloud derived DTM, a LiDAR derived DTM was used for comparison in consonance with several statistical measures of model efficiency. Results demonstrate that the UAS derived DTM can be used in modeling flow and sediment erosion estimation across space in the absence of a LiDAR-based derived DTM.

Estimating Mountain Glacier Flowlines by Local Linear Regression Gradient Descent

Motivated by the need to monitor mountain glaciers, this article addresses the estimation of a mountain glacier's flowline, along which the movement of the glacier's terminus can be captured. We propose a method for estimating glacier flowlines through local linear regression gradient descent (gd-flow) on digital elevation model (DEM) images. We additionally propose an aggregation method (median gd-flow) that increases the accuracy of gd-flow by combining flowlines corresponding to different gd-flow window sizes. We compare gd-flow and median gd-flow to a standard hydrological flow model (D8) and a variant of D8 (D8-smooth), which applies D8 to a smooth DEM, across 25 glaciers using manually drawn flowlines as a reference standard. We assess the performance via simulations considering variable terrain and image quantization. Our proposed algorithm (gd-flow) outperforms D8 and D8-smooth in both applied and simulated settings, while median gd-flow further improves gd-flow by leveraging the accuracy of multiple window sizes.

An Overland Flood Model for Geographical Information Systems

A variety of flood models and commercial flood simulation software are provided in the literature, with different accuracies and precisions changing from coarse to fine, depending on model structure and detailed descriptions of basin and hydrologic properties. These models generally focus on river processes, taking overland processes as inputs of 1D or 2D hydrodynamic or hydrologic river flow models. Due to the discrete structure of overland flow and unknown-dynamic boundary conditions, such classical approaches are not cable of fast and reliable spatio–temporal estimations for overland flows, and require detailed and well-organized spatial data that cannot be immediately obtained during an emergency. A spatially-distributed Geographical Information Systems (GIS) based flood model is developed in this study to simulate overland floods, using cellular automata principles. GIS raster cells are considered hydrologic homogeneous areas throughout which hydrologic properties remain constant. Hydrodynamic flow principles, conservations of mass, momentum and energy are applied at pixel level to simulate floodwaters. The proposed GIS model is capable of directly manipulating spatio–temporal pixel level data (e.g., topography, precipitation, infiltration, surface roughness etc.) for modeling of rainfall-induced overland floods; therefore, it can provide fast, temporal and spatial flood depth estimations as well as maximum flood depths and times of concentration for all pixels throughout a study area. The model is quite simple and easy to apply via easily creatable GIS input layers, and is thus very convenient for preliminary engineering applications that need quick and fast response. Its main advantage is that it does not need a predefined flood boundary and boundary conditions. This advantage is especially valuable for coastal plains where delineation of a basin is generally too difficult. Floodwaters of Cyclone Nargis/Myanmar were simulated to test the model. Sensitivity analyses were applied to evaluate the effects of the model parameters (i.e., surface roughness and infiltration rates) on simulation results. The study shows that the proposed GIS model can be readily applied for the fast and inexpensive modeling of rainfall caused floods in areas where flood boundaries and boundary conditions cannot be clearly identified.

Baltic Sea eutrophication status is not improved by the first pillar of the European Union Common Agricultural Policy

Agriculture is an important source of nitrogen and phosphorous loads to the Baltic Sea. We study how the European Union’s (EU) Common Agricultural Policy (CAP), and in particular how its first pillar, containing most of the budget and the decoupled farm payments, affects eutrophication. To aid our study, we use three simulation models, covering the agricultural sector in the EU, a hydrological nutrient flow model and a model of eutrophication in the Baltic Sea. We compute changes in key eutrophication indicators in a business-as-usual baseline and in a hypothetical situation where the first pillar of the CAP, containing the direct payments, greening and accompanying measures, is not present. Comparing the outcomes, we find that in the scenario without the first pillar, production and agricultural land use is lower, while yields and fertiliser use per hectare are higher, causing less nitrogen and phosphorous loads (0.5 to 4% depending on the basin) and less eutrophication in the Baltic Sea as net effect. We therefore conclude that the policies of the first pillar of the CAP contribute to increased eutrophication in the Baltic Sea.

Integrated hydrogeological modelling of hard-rock semi-arid terrain: supporting sustainable agricultural groundwater use in Hout catchment, Limpopo Province, South Africa

An integrated hydrogeological modelling approach applicable to hard-rock aquifers in semi-arid data-scarce Africa was developed using remote sensing, rainfall-runoff modelling, and a three-dimensional (3D) dynamic model. The integrated modelling approach was applied to the Hout catchment, Limpopo Province, South Africa, an important agricultural region where groundwater abstraction for irrigation doubled during 1968–1986. Since the 1960s, groundwater levels in irrigated areas have displayed extended periods of decline with partial or full recovery in response to major decadal rainfall events or periods. The integrated dynamic 3D hydrogeological flow model, based on the One-Water Hydrologic Flow Model (MODFLOW-OWHM), helped to understand recharge and flow processes and inform water use and management. Irrigation abstraction was estimated based on irrigated crop area delineated using the Landsat Normalized Difference Vegetation Index (NDVI) and crop water requirements. Using groundwater level data, the model was calibrated (2008–2012) and validated (2013–2015). Estimated mean diffuse recharge (3.3 ± 2.5% of annual rainfall) compared well with estimates from the Precipitation Runoff Modelling System model. Recharge and groundwater storage showed significant inter-annual variability. The ephemeral river was found to be losing, with mean net flux to the aquifer (focused recharge) of ~1.1% of annual rainfall. The results indicate a delicate human-natural system reliant on the small but highly variable recharge, propagating through variable pumping to an even more variable storage, making the combined system vulnerable to climate and anthropogenic changes. The integrated modelling is fundamental for understanding spatio-temporal variability in key parameters required for managing the groundwater resource sustainably.

Comparing the Effects of Inputs for NTT and ArcAPEX Interfaces on Model Outputs and Simulation Performance

The Agricultural Policy/Environmental eXtender (APEX) model has five different interfaces used to process and build simulation projects. These interfaces utilize different input databases that lead to different model default values. These values can result in different hydrologic, crop growth, and nutrient flow model outputs. This study compared structural and input value differences of the ArcAPEX and Nutrient Tracking Tool (NTT) interfaces. Long-term, water quality data from the Rock Creek watershed, located in Ohio were used to determine the impact of the differences on computation time, parameter sensitivity, and streamflow, total nitrogen (TN), and total phosphorus (TP) simulation performance. The input structures were the same for both interfaces for all files except soils, where NTT assigns three soil files per field, rather than a single one in ArcAPEX. As a result, computation times were three times as long for NTT as for ArcAPEX. There were twelve sensitive parameters in both cases, but the order of sensitivity was different. Both interfaces simulated streamflow well, but ARCAPEX simulated evapotranspiration, TN, and TP better than NTT, while NTT simulated crop yields better than ArcAPEX. However, none of the models met all of the performance criteria for either interface. Therefore, more work is needed to ensure models are properly calibrated before being used for scenario analysis. While it is acceptable for the values to be different from the SSURGO database, there is no documentation explaining the rationale for the modifications from the original source. This is one of the examples that highlights lack of detailed documentation that would be useful to model users. Overall, the results indicate that different interfaces lead to different model simulation results and, therefore, the authors recommend users specify the interface used and any modifications made to the associated databases when reporting model results.

Impact assessment of coal mining on river water and groundwater and its interaction through hydrological, isotopic characteristics, and simulation flow modeling

Impact assessment of coal mining of Gare IV/6 Coal Block (GCB) on river water (Kelo River) and groundwater and the interaction between them were studied through hydrological studies like water-level monitoring, short and long-term river flow measurements, isotopic characteristics, and groundwater flow modeling. The hydrological study reveals that the groundwater flow is towards the Kelo River and the river is acting as effluent in nature. The flow direction is parallel to Kelo River in the downstream of the GCB. The isotopic study suggests that the Kelo River water is enriched with δ 18O/16O ratio as compared to watershed samples. Flow modeling suggests that the Kelo River, which is adjacent to the boundary of GCB, may contribute 88.38 m3/day of groundwater. The groundwater effluence forms a meager component of the total groundwater effluence estimated for the entire length of the Kelo River passing through the study area. Based on the groundwater flow model results it is suggested that the proposed mining operation in GCB will not have any impact on the Kelo River water flow. The suspected seepage from the Kelo River flooding on the GCB is unlikely as the hydraulic gradient is towards the Kelo River. It is suggested to have a buffer zone and an embankment between Kelo River and GCB to prevent flooding from river water breaching. The present study provides an overall understanding of the hydrogeological conditions in and around mining area which will help in safe mining operations so that any hazard or threat to the local community may be prevented.

LAND USE, MICROCLIMATE, AND SURFACE RUNOFF LINKAGES: SPACE-TIME MODELING FROM ROKEL-SELI RIVER BASIN, SIERRA LEONE

Abstract. This study mainly utilized the Soil and Water Assessment Tool (SWAT) together with SWAT-CUP, both free and open source software (FOSS), to construct a distributed hydrologic flow model for the Rokel-Seli River basin, Sierra Leone, in a bid to spatiotemporally evaluate the role of changes in land use/land cover (LULC) and microclimate on streamflow regimes. The model was informed by LULC data derived from three Landsat satellite images collected in 2002, 2010, and 2016. The LULC data was generated with the aid of several python libraries accessed through the FOSS Anaconda Navigator. LULC change analysis demonstrated that between 2002 and 2016, urban, agricultural, water, and mining lands expanded significantly but forest cover reduced the most (−5.7 %). While average annual surface runoff dramatically increased from 2002 to 2010 (31.7 %), the period after the reservoir construction (2010–2016) recorded lower increase in surface runoff (0.9 %). Result of the study suggested that the construction of a major reservoir to support hydroelectricity in concert with significant loss of forest cover and shrub played a greater role in increasing surface runoff compared with the influence of microclimate.

Use of rainfall forecast from a high-resolution global NWP model in a hydrological stream flow model over Narmada river basin during monsoon

Use of NWP model rainfall forecast is useful for hydrological modelling for river basins for flood and water management. In this study, the SWAT model is applied to the Narmada river basin to estimate the surface runoff. The capability of the model is tested for the south west monsoon season (June–September) of 2016 and validated against the NCUM global NWP model forecast data up to Day-5. Two heavy rainfall events are used for verification of the global model forecast with the observed data. The two verification events occurring during 1 July to 15 July (mean of 15 days) and 30 Aug to 11 Sept (mean of 12 days) are considered. Using Arc GIS sub watershed boundaries, the drainage network, slope, land use map and soil map are generated for the whole Narmada river basin. The surface runoff is computed by forcing with observed rainfall data as well as the NCUM model rainfall forecasts data as input to the SWAT model. Model simulations are compared at five stations of Narmada namely—Balkheri, Sandia, Handia, Hoshangabad and Garudeshwar. Initially, the NCUM model rainfall forecast is compared with the actual observation to evaluate the model performances in terms of bias estimation. Then the surface runoff is computed using the observed rainfall data and NCUM forecast data up to Day-5 and made a comparison to evaluate the SWAT model performances. It is shown that the estimated surface runoff during the two active phases is simulated well with some overestimation during the season. The skill of hydrological simulations is examined during different length of forecasts. It is seen that the SWAT model output performance is related to the NWP rainfall forecast skills. NCUM global NWP model is overestimating rainfall amount (wet bias) by 50–70 mm/day over the basin during the two active phases. Further, in all the days’ forecasts, the model is showing wet bias over the upper part of the Narmada river basin and a dry bias over the lower part of the basin. The dry bias is seen to be around 5–35 mm/day.

Optimal Remediation Scheme for a Wastewater Recharge Site: Contaminants Fate and Transport Model.

A 3-dimensional hydrologic groundwater flow and contaminant transport model was developed to address the feasibility and relevant time-scales for remediation of a large soil aquifer treatment (SAT) site for domestic wastewater. The model accounted for a range of organic pollutant retardation factors and biodegradation kinetics. In order to detect the effect of the most retained and the most refracted/recalcitrant pollutants, it was crucial to model fractions of different properties rather than with average set properties. Four aquifer remediation scenarios, including two active washing procedures and two involving natural attenuation, were evaluated. The remediation efficiencies, in terms of residual plume size and mass of pollutant washout, were compared to each other and to the current operation scheme. According to the results, remediation mainly via natural attenuation rather than some form of intense pump and treat technology, is feasible, unlike the situation with hazardous waste sites. Enforced washout becomes less efficient with time due to increasing retardation of the residual pollutants. Therefore, pollution containment with natural biodegradation, which removed 95% of the emerging contaminants within 30 to 40 years was found to be the most valuable remediation scheme.

Hydrological stream flow modeling in the Talar catchment (central section of the Alborz Mountains, north of Iran): Parameterization and uncertainty analysis using SWAT-CUP

AbstractThere are several methods and techniques for measuring the parameters and forecasting the errors in the hydrological models. In this study, semi distributed Soil and Water Asseeement Tool (SWAT) model and SWAT-CUP (CUP – Calibration and Uncertainty Programs) have been applied using SUFI2 program. After collection of data, the whole Talar watershed located in the central section of the Alborz Mountains, north of Iran was separated into 219 hydrological response units (HRU) in 23 sub-watersheds.In order to improve the simulation parameters and obtain better correlation of observed and simulated values, the sensitive parameters were validated to obtain finally the acceptable value of both R 2 and Nash–Sutcliffe (NS) coefficients equal to 0.93. Final P-value and t-state were also estimated for sensitive parameters. As a result, the CN2 parameter, which was critical in the initial stage of this research was replaced by the SOL-K parameter (electrical conductivity saturated soil layers) as a critical parameter in the later stage. Results of this study show that the SWAT model can be an effective and useful tool for the assessment and optimal management of water and soil resources.

A comparison of results from a hydrologic transport model (HSPF) with distributions of sulfate and mercury in a mine-impacted watershed in northeastern Minnesota

The St. Louis River watershed in northeast Minnesota hosts a major iron mining district that has operated continuously since the 1890s. Concern exists that chemical reduction of sulfate that is released from mines enhances the methylation of mercury in the watershed, leading to increased mercury concentrations in St. Louis River fish. This study tests this idea by simulating the behavior of chemical tracers using a hydrologic flow model (Hydrologic Simulation Program FORTRAN; HSPF) and comparing the results with measured chemistry from several key sites located both upstream and downstream from the mining region. It was found that peaks in measured methylmercury (MeHg), total mercury (THg), dissolved organic carbon (DOC), and dissolved iron (Fe) concentrations correspond to periods in time when modeled recharge was dominated by active groundwater throughout the watershed. This helps explain why the timing and size of the MeHg peaks was nearly the same at sites located just upstream and downstream from the mining region. Both the modeled percentages of mine water and the measured sulfate concentrations were low and computed transit times were short for sites downstream from the mining region at times when measured MeHg reached its peak. Taken together, the data and flow model imply that MeHg is released into groundwater that recharges the river through riparian sediments following periods of elevated summer rainfall. The measured sulfate concentrations at the upstream site reached minimum concentrations of approximately 1 mg/L just as MeHg reached its peak, suggesting that reduction of sulfate from non-point sources exerts an important influence on MeHg concentrations at this site. While mines are the dominant source of sulfate to sites downstream from them, it appears that the background sulfate which is present at only 1–6 mg/L, has the largest influence on MeHg concentrations. This is because point sourced sulfate is transported generally under oxidized conditions and is not flushed through riparian sediments in a gaining stream watershed system.

Application of run-off model as a contribution to the torrential flood risk management in Topčiderska Reka watershed, Serbia

This paper deals with developing of hydrological flow model for the torrential watershed of the Topciderska River, located in the Belgrade macro-region, in which torrential flood events have had destructive human and material consequences. The aim of the paper was to show that model, developed by hydrological software SHETRAN, is useful tool enabling the simulation of physical properties and hydrological processes in watersheds, having a significant place in decision support system within the torrential flood risk management. Results achievement was enabled through three phases: (1) Sensitivity analysis showed that the closest hydrograph to registered hydrograph is modelled with averaged values of parameters; (2) model calibration was done by calibration of four main parameters with significant influence on flow component (hydraulic conductivity of soil and rock, Strickler roughness coefficient for overland and river network flow) in case of the torrential flood event from 10th July 1999; and (3) model verification was done by input of calibrated values in case of two another torrential flood events (1996, 1999). Statistical analysis of correspondence of modelled and registered discharges showed that due to correlation coefficient (0.95–0.98) and determination coefficient (0.90–0.96) as well as probability of error according to F test, good results are achieved. Considering obtained results, developed model should be a part of torrential flood risk management in watershed of Topciderska River.

Adaptive hydrological flow field modeling based on water body extraction and surface information

Suranaree University of Technology, School of Computer Engineering,111 University Avenue, Muang, Nakhon Ratchasima 30000, ThailandAbstract. Hydrological flow characteristic is one of the prime indicators for assessing flood.It plays a major part in determining drainage capability of the affected basin and also in thesubsequent simulation and rainfall-runoff prediction. Thus far, flow directions were typicallyderived from terrain data which for flat landscapes are obscured by other man-made structures,hence undermining the practical potential. In the absence (or diminutive) of terrain slopes, waterpassageshaveamorepronouncedeffectonflowdirectionsthanelevations.Thispaper,therefore,presents detailed analyses and implementation of hydrological flow modeling from satellite andtopographicimages.Herein,gradualassignmentbasedonsupportvectormachinewasappliedtomodified normalized difference water index and a digital surface model, in order to ensure reli-able water labeling while suppressing modality-inherited artifacts and noise. Gradient vectorflow was subsequently employed to reconstruct the flow field. Experiments comparing theproposed scheme with conventional water boundary delineation and flow reconstruction werepresented. Respective assessments revealed its advantage over the generic stream burning.Specifically, it could extract water body from studied areas with 98.70% precision, 99.83%recall, 98.76% accuracy, and 99.26% F-measure. The correlations between resultant flowsand those obtained from the stream burning were as high as 0.80 0.04 (p ≤ 0.01 in all res-olutions).

Regional Hazard Analysis For Use In Vulnerability And Risk Assessment

Abstract A method for supporting an operational regional risk and vulnerability analysis for hydrological hazards is suggested and applied in the Island of Cyprus. The method aggregates the output of a hydrological flow model forced by observed temperatures and precipitations, with observed discharge data. A scheme supported by observed discharge is applied for model calibration. A comparison of different calibration schemes indicated that the same model parameters can be used for the entire country. In addition, it was demonstrated that, for operational purposes, it is sufficient to rely on a few stations. Model parameters were adjusted to account for land use and thus for vulnerability of elements at risk by comparing observed and simulated flow patterns, using all components of the hydrological model. The results can be used for regional risk and vulnerability analysis in order to increase the resilience of the affected population.

Unsaturated zone hydrology and cave drip discharge water response: Implications for speleothem paleoclimate record variability

Summary High-frequency, spatially-dense discharge monitoring was conducted over fifteen months to characterise unsaturated zone flow at Harrie Wood Cave (HWC), in the Snowy Mountains, Yarrangobilly (SE Australia). The cave was formed in the Late Silurian Yarrangobilly Limestone, a fractured rock associated with very low primary porosity due to past diagenesis. Over our monitoring period we simultaneously measured rainfall, soil moisture saturation and drip discharge rate at fourteen sites to characterise infiltration–discharge relationships. All drip discharge sites exhibited non-Gaussian distributions, indicating long periods where low discharge predominates, punctuated by short infrequent periods of high discharge. However, there was significant variability in discharge between sites and consequently no spatial correlation in the cave. We investigated the depth–discharge relationship at HWC and found a moderate relationship between depth and drip discharge lag (response) times to soil moisture content, but only weak relationships between depth and mean and maximum discharge. This highlights that the karst architecture plays an important role in controlling drip discharge dynamics. Principal Component Analysis (PCA) and Agglomerative Hierarchal Clustering (AHC) were used to classify similar drip types, revealing five unique drip regimes. Two-phase flow and non-linear response to recharge behaviour were observed, suggesting secondary porosity is controlling unsaturated zone flow in mature limestone environments with low primary porosity. Using the data presented here, the first coupled conceptual and box hydrological flow model was developed. This study highlights the heterogeneous nature of hydrological flow in karst and the need to understand unsaturated zone hydrology at the individual drip discharge level, to inform speleothem studies for high-resolution paleoclimate reconstruction.

Hydrological Stream Flow Modelling for Calibration and Uncertainty Analysis Using SWAT Model in the Xedone River Basin, Lao PDR

The hydrological stream flow modeling is applied by the Soil for Water Assessment Tool (SWAT) model in the Xedone River basin, covering an area of 7,224.61 km2, in the southern part of Laos. The main objective of this research is to test the performance and feasibility of the SWAT model for predicting stream flow in the river basin. The model is calibrated and validated for two periods: 1993-2000 and 2001-2008, respectively, by using the SUFI-2 technique in this analysis. The SUFI-2 gives good results with the high value of R2 and NSE larger than 0.70 respectively, for daily simulation. Monthly simulation results during calibration and validation are also good with R2> 0.80 and NSE > 0.80. The sensitivity analysis results of the model to each sub-basin delineation and hydrological response unit (HRU) in this basin are 230 HRUs in the whole basin. For uncertainty results, the 95% prediction uncertainty (95PPU) brackets very well with the observed discharge. All of sources uncertainty results are captured by bracketing value, higher than 65% of the observed river discharge. All of the results in this study are important to water discharge. The calibrated model can be used for further analysis of the effects of the climate and land use change, water quality analysis and sediment yield analysis; furthermore, the modelling can be applied for planning dam construction in the future and flood disaster risk management and thereby is useful for the sustainable development of the country.