Water Travel Time Research Articles

Household Deficiency in Demand for Water: Do Water Source and Travel Time Matter?

Despite the massive commitment by policy makers and stakeholders to increase the supply of water to households, many households have a deficiency in their daily quantity of water required for drinking and for general use. This paper focuses on the effect of water source and travelling time on households’ deficiency in demand for water using the GLSS6 data. A Tobit regression analysis of data on 2843 households reveals that a 1 minute increase in travelling time increases household deficiency in water demand by about 8 l (49%). Also, compared to pipe in dwelling/yard/plot, all other sources of water to the households come with greater levels of water deficiency. Government policies should focus on making more resources available to the Ghana Water Company Limited and the Community Water and Sanitation Agency so as to achieve more coverage of water accessible to both urban and rural households.

A study on mountain front recharge by using integrated techniques in the hard rock aquifers of southern India

Mountain front recharge (MFR) is the contribution of mountains to recharge the aquifers in the adjacent basins. The estimation of MFR is essential to obtain a detailed investigation of recharge of the groundwater at the mountain front. This study summarises the current understanding of recharge processes by comparing daily groundwater fluctuation to daily rainfall and identifies the recharge rates. The recharge rates vary with time due to difference in water table depth and travel time. Thus to understand the MFR along the foothills of Courtallam, a total of 14 surface water, rainwater and groundwater samples were collected and measured for stable isotopes. The isotopic data were used to investigate the recharge process and to identify the elevations to recharge. The study findings also suggest that predominantly rainfall along the foothills contributes recharge to the riparian zone (basin block region), whereas foothill regions receive recharge from rainfall over mountain block.

Time‐variant Lagrangian transport formulation reduces aggregation bias of water and solute mean travel time in heterogeneous catchments

AbstractLack of hydro‐bio‐chemical data at subcatchment scales necessitates adopting an aggregated system approach for estimating water and solute transport properties, such as residence and travel time distributions, at the catchment scale. In this work, we show that within‐catchment spatial heterogeneity, as expressed in spatially variable discharge‐storage relationships, can be appropriately encapsulated within a lumped time‐varying stochastic Lagrangian formulation of transport. This time (variability) for space (heterogeneity) substitution yields mean travel times (MTTs) that are not significantly biased to the aggregation of spatial heterogeneity. Despite the significant variability of MTT at small spatial scales, there exists a characteristic scale above which the MTT is not impacted by the aggregation of spatial heterogeneity. Extensive simulations of randomly generated river networks reveal that the ratio between the characteristic scale and the mean incremental area is on average independent of river network topology and the spatial arrangement of incremental areas.

Water storage dynamics in a till hillslope: the foundation for modeling flows and turnover times

AbstractStudies on hydrology, biogeochemistry, or mineral weathering often rely on assumptions about flow paths, water storage dynamics, and transit times. Testing these assumptions requires detailed hydrometric data that are usually unavailable at the catchment scale. Hillslope studies provide an alternative for obtaining a better understanding, but even on such well‐defined and delimited scales, it is rare to have a comprehensive set of hydrometric observations from the water divide down to the stream that can constrain efforts to quantify water storage, movement, and turnover time. Here, we quantified water storage with daily resolution in a hillslope during the course of almost an entire year using hydrological measurements at the study site and an extended version of the vertical equilibrium model. We used an exponential function to simulate the relationship between hillslope discharge and water table; this was used to derive transmissivity profiles along the hillslope and map mean pore water velocities in the saturated zone. Based on the transmissivity profiles, the soil layer transmitting 99% of lateral flow to the stream had a depth that ranged from 8.9 m at the water divide to under 1 m closer to the stream. During the study period, the total storage of this layer varied from 1189 to 1485 mm, resulting in a turnover time of 2172 days. From the pore water velocities, we mapped the time it would take a water particle situated at any point of the saturated zone anywhere along the hillslope to exit as runoff. Our calculations point to the strengths as well as limitations of simple hydrometric data for inferring hydrological properties and water travel times in the subsurface.

Hysteresis effects in organic matter turnover in a tropical floodplain during a flood cycle

Tropical inland waters are increasingly recognized for their role in the global carbon cycle, but uncertainty about the effects of such systems on the transported organic matter remains. The seasonal interactions between river, floodplain, and vegetation result in highly dynamic systems, which can exhibit markedly different biogeochemical patterns throughout a flood cycle. In this study, we determined rates and governing processes of organic matter turnover. Multi-probes in the Barotse Plains, a pristine floodplain in the Upper Zambezi River (Zambia), provided a high-resolution data set over the course of a hydrological cycle. The concentrations of oxygen, carbon dioxide, dissolved organic carbon, and suspended particulate matter in the main channel showed clear hysteresis trends with expanding and receding water on the floodplain. Lower oxygen and suspended matter concentrations prevailed at longer travel times of water in the floodplain, while carbon dioxide and dissolved organic carbon concentrations were higher when the water spent more time on the floodplain. Maxima of particulate loads occurred before highest water levels, whereas the maximum in dissolved organic carbon load occurred during the transition of flooding and flood recession. Degradation of terrestrial organic matter occurred mainly on the floodplain at increased floodplain residence times. Our data suggest that floodplains become more intense hotspots at prolonged travel time of the flood pulse over the floodplain.

Inferring changes in water cycle dynamics of intensively managed landscapes via the theory of time‐variant travel time distributions

Climatic trends and anthropogenic changes in land cover and land use are impacting the hydrology and water quality of streams at the field, watershed, and regional scales in complex ways. In poorly drained agricultural landscapes, subsurface drainage systems have been successful in increasing crop productivity by removing excess soil moisture. However, their hydroecological consequences are still debated in view of the observed increased concentrations of nitrate, phosphorus, and pesticides in many streams, as well as altered runoff volumes and timing. In this study, we employ the recently developed theory of time-variant travel time distributions within the StorAge Selection function framework to quantify changes in water cycle dynamics resulting from the combined climate and land use changes. Our results from analysis of a subbasin in the Minnesota River Basin indicate a significant decrease in the mean travel time of water in the shallow subsurface layer during the growing season under current conditions compared to the pre-1970s conditions. We also find highly damped year-to-year fluctuations in the mean travel time, which we attribute to the “homogenization” of the hydrologic response due to artificial drainage. The dependence of the mean travel time on the spatial heterogeneity of some soil characteristics as well as on the basin scale is further explored via numerical experiments. Simulations indicate that the mean travel time is independent of scale for spatial scales larger than approximately 200 km2, suggesting that hydrologic data from larger basins may be used to infer the average of smaller-scale-driven changes in water cycle dynamics.

Decoupling of carbon dioxide and dissolved organic carbon in boreal headwater streams

AbstractStreams and rivers emit large quantities of carbon dioxide (CO2) to the atmosphere. The sources of this CO2 are in‐stream mineralization of organic carbon (OC) and CO2 input via groundwater inflow, but their relative importance is largely unknown. In this study, we quantified the role of in‐stream OC mineralization as a source of CO2 in a number of nested boreal headwater streams. The results showed that mineralization of stream OC contributed 3% of CO2 supersaturation at time scales comparable to the estimated water travel times in the streams (<24 h). Mass balances showed that downstream losses of OC were ≤3% in low‐order streams, whereas up to 16% of the OC was lost in the largest (fourth order) streams. In contrast, 85% of the CO2 was lost along the stream network (longest total stream length = 17 km). Under the assumption that in‐stream OC mineralization was the main source of stream CO2, higher rates of OC mineralization (6% of OC) than those reported across the literature (≤0.7% of OC) would be required to sustain observed CO2 supersaturation. Further, model results indicated that groundwater inflows were sufficient to sustain observed stream CO2 concentrations. We hence conclude that in‐stream OC mineralization was a minor source of CO2 in these boreal headwater systems and that the main source of stream CO2 was inflowing groundwater transporting CO2 originating from soil respiration.

Simultaneous-Irrigation Scheduling GA Model with Identical Discharges and Travel Time

AbstractMultimachine scheduling problems with earliness/tardiness costs and sequence-dependent setup times are analogous to the simultaneous irrigation scheduling problem with water travel times be...

Root-zone plant available water estimation using the SMOS-derived soil water index

Currently, there are several space missions capable of measuring surface soil moisture, owing to the relevance of this variable in meteorology, hydrology and agriculture. However, the Plant Available Water (PAW), which in some fields of application could be more important than the soil moisture itself, cannot be directly measured by remote sensing. Considering the root zone as the first 50cm of the soil, in this study, the PAW at 25cm and 50cm and integrated between 0 and 50cm of soil depth was estimated using the surface soil moisture provided by the Soil Moisture Ocean Salinity (SMOS) mission. For this purpose, the Soil Water Index (SWI) has been used as a proxy of the root-zone soil moisture, involving the selection of an optimal T (Topt), which can be interpreted as a characteristic soil water travel time. In this research, several tests using the correlation coefficient (R), the Nash-Sutcliffe score (NS), several error estimators and bias as predictor metrics were applied to obtain the Topt, making a comprehensive study of the T parameter. After analyzing the results, some differences were found between the Topt obtained using R and NS as decision metrics, and that obtained using the errors and bias, but the SWI showed good results as an estimator of the root-zone soil moisture. This index showed good agreement, with an R between 0.60 and 0.88.The method was tested from January 2010 to December 2014, using the database of the Soil Moisture Measurements Stations Network of the University of Salamanca (REMEDHUS) in Spain. The PAW estimation showed good agreement with the in situ measurements, following closely the dry-downs and wetting-up events, with R ranging between 0.60 and 0.92, and error values lower than 0.05 m3m−3. A slight underestimation was observed for both the PAW and root-zone soil moisture at the different depths; this could be explained by the underestimation pattern observed with the SMOS L2 soil moisture product, in line with previous studies. Nevertheless, the results obtained in this research showed an encouraging improvement of the PAW estimation. Despite the need for more research on this issue, the results of this study show that this methodology can be useful for applications of great interest in agriculture and hydrology.

Travel times in the vadose zone: Variability in space and time

AbstractWater travel times reflect hydrological processes, yet we know little about how travel times in the unsaturated zone vary with time. Using the soil physical model HYDRUS‐1D, we derived time variable travel time distributions for 35 study sites within the Attert catchment in Luxembourg. While all sites experience similar climatic forcing, they differ with regard to soil types (16 Cambisols, 12 Arenosols, and 7 Stagnosols) and the vegetation cover (29 forest and 6 grassland). We estimated site specific water flow and transport parameters by fitting the model simulations to observed soil moisture time series and depth profiles of pore water stable isotopes. With the calibrated model, we tracked the water parcels introduced with each rainfall event over a period of several years. Our results show that the median travel time of water from the soil surface to depths down to 200 cm is mainly driven by the subsequent rainfall amounts. The median time until precipitation is taken up by roots is governed by the seasonality of evapotranspiration rates. The ratio between the amount of water that leaves the soil profile by on the one hand and evaporation and transpiration on the other hand also shows an annual cycle. This time variable response due to climatic forcing is furthermore visible in the multimodal nature of the site specific master transit time distribution representing the flow‐averaged probability density for rainwater to become recharge. The spatial variability of travel times is mainly driven by soil texture and structure, with significant longer travel times for the clayey Stagnosols than for the loamy to sandy Cambisols and Arenosols.

Spring response to precipitation events using δ18O and δ2H in the Tanour catchment, NW Jordan

ABSTRACTThe Tanour spring is one of the several karst springs located in the northern part of Jordan. Water samples from the Tanour spring and precipitation were collected in the area of Ajloun in NW Jordan for the analysis of stable oxygen and hydrogen isotopes to evaluate the spring response to precipitation events. Rainwater and snow samples were collected from different elevations during winters of 2013–2014 and 2014–2015. In addition, spring samples were collected between December 2014 and March 2015. δ18O values in rainwater vary from −3.26 to −17.34 ‰ (average: −7.84 ± 3.23 ‰), while δ2H values range between −4.4 and −110.4 ‰ (average: −35.7 ± 25.0 ‰). Deuterium excess ranges from 17.8 to 34.1 ‰ (average: 27.1 ± 4.0 ‰). The Local Meteoric Water Line for the study area was calculated to be δ2H = 7.66*δ18O + 24.43 (R2 = 0.98). Pre-event spring discharge showed variation in δ18O (range −6.29 to −7.17 ‰; average −6.58 ± 0.19 ‰) and δ2H values (range −28.8 to −32.7 ‰; average: −30.5 ± 1.0 ‰). In contrast, δ18O and δ2H rapidly changed to more negative values during rainfall and snowmelt events and persisted for several days before returning to background values. Spring water temperature, spring discharge, and turbidity followed the trend in isotopic composition during and after the precipitation events. The rapid change in the isotopic composition, spring discharge, water temperature, and turbidity in response to recharge events is related to fast water travel times and low storage capacity in the conduit system of the karst aquifer. Based on the changes in the isotopic composition of spring water after the precipitation events, the water travel time in the aquifer is in the order of 5–11 days.

Capture zone delineation methodology based on the maximum concentration: Preventative groundwater well protection areas for heat exchange fluid mixtures

AbstractCapture zones of water supply wells are most often delineated based on travel times of water or solute to the well, with the assumption that if the travel time is sufficiently large, the concentration of chemical at the well will not exceed the drinking water standards. In many situations, the likely source concentrations or release masses of contamination from the potential sources are unknown; therefore, the exact concentration at the well cannot be determined. In situations in which the source mass can be estimated with some accuracy, the delineation of the capture zone should be based on the maximum chemical concentration that can be expected at the well, rather than on an arbitrary travel time. We present a new capture zone delineation methodology that is based on this maximum chemical concentration. The method delineates capture zones by solving the adjoint of the advection‐dispersion‐reaction equation and relating the adjoint state and the known release mass to the expected chemical concentration at the well. We demonstrate the use of this method through a case study in which soil heat exchange systems are potential sources of contamination. The heat exchange fluid mixtures contain known fluid volumes and chemical concentrations; thus, in the event of a release, the release mass of the chemical is known. We also demonstrate the use of a concentration basis in quantifying other measures of well vulnerability including exposure time and time to exceed a predefined threshold concentration at the well.

Watershed structural influences on the distributions of stream network water and solute travel times under baseflow conditions

AbstractWatershed structure influences the timing, magnitude, and spatial location of water and solute entry to stream networks. In turn, stream reach transport velocities and stream network geometry (travel distances) further influence the timing of export from watersheds. Here, we examine how watershed and stream network organization can affect travel times of water from delivery to the stream network to arrival at the watershed outlet. We analysed watershed structure and network geometry and quantified the relationship between stream discharge and solute velocity across six study watersheds (11.4 to 62.8 km2) located in the Sawtooth Mountains of central Idaho, USA. Based on these analyses, we developed stream network travel time functions for each watershed. We found that watershed structure, stream network geometry, and the variable magnitude of inputs across the network can have a pronounced affect on water travel distances and velocities within a stream network. Accordingly, a sample taken at the watershed outlet is composed of water and solutes sourced from across the watershed that experienced a range of travel times in the stream network. We suggest that understanding and quantifying stream network travel time distributions are valuable for deconvolving signals observed at watershed outlets into their spatial and temporal sources, and separating terrestrial and in‐channel hydrological, biogeochemical, and ecological influences on in‐stream observations. Copyright © 2016 John Wiley & Sons, Ltd.

Integrating Variable Wind Power Using a Hydropower Cascade

In this paper, we examine the ability of a hydropower cascade to balance variability from wind power. We consider a coordinated hydro-wind system that satisfies a single power balance, and we use a real-time control scheme to optimize system operations such that wind and load curtailment is minimized. The control scheme considers system hydraulics (including dynamic tailrace elevations and water travel times) and system constraints. Generation from an individual hydropower plant is modeled using a convex piecewise planar approximation. We give results from a case study involving hydro and wind power in the Pacific Northwest region of the United States. The objective of this paper is to present a framework for evaluating how the regulation of wind generation affects hydropower operations. Our intention is to use this framework in future work to perform a systematic study of balancing capability across different hydraulic conditions, system constraints, and wind generation scenarios.

Modelling winter operational strategies of a hydropower system

The ice conditions in regulated rivers can be very complicated due to both intake and release of water to and from hydropower plants. The optimal operational strategies for the hydropower system must involve ice management in the river basin and finding a balance can be a challenge for the hydropower operator. Issues with ice occur during both freezeup and breakup, and at certain conditions both situations can occur in a basin at nearly the same time. In this study, a series of modelling tools have been used to investigate the consequences of a forced shutdown of a power plant in the Orkla River. The associated impacts on the stability of the ice cover in a downstream bypass reach and the ice and ecological conditions in the reaches upstream of the power plant have been explored. The reason for this is that there are restrictions on upstream water releases during the shutdown period given in the regulation permit to prevent ice breakup in the downstream bypass reach and subsequent flooding problems downstream. The study demonstrates a wide application of numerical tools for environmental impact assessment, providing knowledge for better decision-making and for optimal operational strategies for hydropower systems during winter.In summary, the analysis shows that a shutdown period shorter than the travel time of water from the upstream hydropower plants to the bypassed reach does not guarantee a reduction of the ice problems in the bypass reach. Since the intake pond is too small to store already released water from the upstream power plants, spill and ice breakup will occur. It is rather found that a shutdown of the upstream power plants can induce environmental problems due to the rapid dewatering of the river, and an ice breakup during the restart of the upstream power plants.

Simulation-Optimization Approach for Evaluating the Feasibility of Managed Aquifer Recharge in the Samail Lower Catchment, Oman

AbstractThis article presents a simulation-optimization approach for evaluating the feasibility of managed aquifer recharge (MAR) in the Samail Lower Catchment, Oman. The objective is to provide a maximum recharge and extraction rate through MAR in an annual cycle of two successive injection and recovery periods, while meeting operational and system constraints such as water level, gradient, and travel time. Three groundwater management problems were solved by coupling a simulation model with successive linear programming (SLP) and the nondominated sorting genetic algorithm (NSGA-II) multiobjective genetic algorithm. Sensitivity analysis was also completed to examine the overall response of the simulation-optimization results to changes in hydraulic conductivities and maximum injection rates. Results using the SLP algorithm showed that the total volume of injected water for 4 months of injection without recovery is as high as 8×106 m3, and the total recovered volume of water for 4 months injection and 8 ...

Fate of Extended-Spectrum β-Lactamase-Producing Escherichia coli from Faecal Sources in Surface Water and Probability of Human Exposure through Swimming.

The goal of this study was to determine the fate of ESBL-producing Escherichia coli (ESBL-EC) emitted from faecal sources in surface water, and the probability of human exposure through swimming. Concentrations of ESBL-EC were measured in recreational waters and in source waters, being water in ditches surrounding poultry farms and municipal wastewater. Additionally, the potential of ESBL-EC in source waters to reach recreational waters located downstream of these sources was modeled. Modeled ESBL-EC concentrations in recreational waters appeared to be mostly determined by the concentrations in the source waters and by subsequent dilution in surface water, and less by inactivation. The mean (95%) risk of human exposure to ESBL-EC per person per swimming event, as assessed from measured ESBL-EC concentrations in recreational waters, was 0.16 (0.89) for men, 0.13 (0.72) for women and 0.20 (0.95) for children. Similar exposure risks were estimated for hypothetical recreational waters containing 100- or 1000-times diluted source water, located 10 days water travel time downstream of the sources. Human exposure to ESBL-EC through swimming is likely, if recreational waters are located downstream of poultry farms and municipal wastewater discharge points.

Stochastic optimization model for the weekly scheduling of a hydropower system in day-ahead and secondary regulation reserve markets

Hydropower stands out for its fast response ability and flexible operation, playing a predominant role in the provision of regulation reserves. As hydro power is an energy-constrained generation technology, it needs to be protected against any possible deployment of the scheduled reserves. However, the few models that formulate a detailed hourly co-optimization of energy and regulation reserves, neglect infeasibilities that could be derived from the requested reserves in real-time. As the regulation reserve market is becoming increasingly important, hydro producers can no longer neglect such effect. This paper presents a stochastic optimization model to find the optimal hourly schedule of a set of hydraulically coupled hydropower plants to obtain the weekly operation that simultaneously maximizes the expected profit in both energy and regulation reserves markets. The model is formulated for a price-taker agent, and it considers a very detailed representation of the system including minimum–maximum water flows, net head dependency, and fractional water travel time. The main contribution is that the obtained solution protects a multi-reservoir system against risk of water and storage unavailability due to the uncertainty in real-time use of regulation-up and down reserves, respectively, and that the reserves deem the net head dependency. The paper presents a realistic case study where the proposed formulation has been tested successfully with real data from the Spanish electricity market.

Impact of degrading permafrost on subsurface solute transport pathways and travel times

Subsurface solute transport under surface warming and degrading permafrost conditions is studied using a physically based model of coupled cryotic and hydrogeological flow processes combined with a particle tracking method. Changes in the subsurface water and inert solute pathways and travel times are analyzed for different modeled geological configurations. For all simulated cases, the minimum and mean travel times increase nonlinearly with warming irrespective of geological configuration and heterogeneity structure. The timing of the start of increase in travel time depends on heterogeneity structure, combined with the rate of permafrost degradation that also depends on material thermal and hydrogeological properties. The travel time changes depend on combined warming effects of: i) increase in pathway length due to deepening of the active layer, ii) reduced transport velocities due to a shift from horizontal saturated groundwater flow near the surface to vertical water percolation deeper into the subsurface, and iii) pathway length increase and temporary immobilization caused by cryosuction-induced seasonal freeze cycles.

Spatial Variability of Dissolved Organic and Inorganic Carbon in Subarctic Headwater Streams

The subarctic landscape is composed of a complex mosaic of vegetation, geology and topography, which control both the hydrology and biogeochemistry of streams across space and time. We present a synoptic sampling campaign that aimed to estimate dissolved C export variability under low-flow conditions from a subarctic landscape. The results included measurements of stream discharge and concentrations of both dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and carbon dioxide (CO2) for 32 subcatchments of the Abiskojokka catchment in northern Sweden. For these subarctic headwater streams, we found that DOC, DIC and CO2 concentrations showed significant variability (p < 0.05) relative to catchment size, discharge, specific discharge, lithology, electrical conductivity, weathering products, and the estimated travel time of water through the subcatchment. Our results indicate that neither vegetation cover nor lithology alone could explain the concentrations and mass flux rates of DOC and DIC. Instead, we found that mass flux rates of DOC, DIC, and CO2 depended mainly on specific discharge and water travel time. Furthermore, our results demonstrate the importance of studying lateral carbon transport in combination with hydrological flow paths at small scales to establish a knowledge foundation applicable for expected carbon cycle and hydroclimatic shifts due to climate change.