Temporal and spatial variations in water flow and sediment load in Narmada River Basin, India: natural and man-made factors

The Narmada River flows through the Deccan volcanics and transports water and sediments to the adjacent Arabian Sea. In a first-ever attempt, spatial and temporal (annual, seasonal, monthly and daily) variations in water discharge and sediment loads of Narmada River and its tributaries and the probable causes for these variations are discussed. The study has been carried out with data from twenty-two years of daily water discharge at nineteen locations and sediment concentrations data at fourteen locations in the entire Narmada River Basin. Water flow in the river is a major factor influencing sediment loads in the river. The monsoon season, which accounts for 85 to 95% of total annual rainfall in the basin, is the main source of water flow in the river. Almost 85 to 98% of annual sediment loads in the river are transported during the monsoon season (June to November). The average annual sediment flux to the Arabian Sea at Garudeshwar (farthest downstream location) is 34.29×10⁶ t year⁻¹ with a water discharge of 23.57 km³ year⁻¹. These numbers are the latest and revised estimates for Narmada River. Water flow in the river is influenced by rainfall, catchment area and groundwater inputs, whereas rainfall intensity, geology/soil characteristics of the catchment area and presence of reservoirs/dams play a major role in sediment discharge. The largest dam in the basin, namely Sardar Sarovar Dam, traps almost 60–80% of sediments carried by the river before it reaches the Arabian Sea.     

Mixing of event and pre‐event water in a shallow Entisol in sloping farmland based on isotopic and hydrometric measurements,SW China

Water percolation and flow processes in subsurface geologic media play an important role in determining the water source for plants and the transport of contaminants or nutrients, which is essential for water resource management and the development of measures for pollution mitigation. During June 2013, the dynamics of the rainwater, soil water, subsurface flows and groundwater in a shallow Entisol on sloping farmland were monitored using a hydrometric and isotopic approach. The results showed that effective mixing of rainwater and soil water occurred in hours. The rebound phenomenon of δD profiles in soils showed that most isotope‐depleted rainwater largely bypassed the soil matrix when the water saturation in the soil was high. Preferential‐flow, which was the dominant water movement pattern in the vadose zone, occurred through the whole soil profile, and infrequent piston‐flow was mainly found at 20–40 cm in depth. The interflow in the soil layer, composed of 75.2% rainwater, was only generated when the soil profile had been saturated. Underflow in the fractured mudrock was the dominant flow type in this hillslope, and outflow was dominated by base flow (groundwater flow) with a mean contribution of 76.7%. The generation mechanism of underflow was groundwater ridging, which was superimposed upon preferential‐flow composed mainly of rainwater. The quick mixing process of rainwater and soil water and the rapid movement of the mixture through preferential channels in the study soil, which shows a typical bimodal pore size distribution, can explain the prompt release of pre‐event water in subsurface flow. Water sources of subsurface flows at peak discharge could be affected by the antecedent soil water content, rain characteristics and antecedent groundwater levels. Copyright © 2016 John Wiley & Sons, Ltd.     

Impacts of groundwater flow on the evolution of a thermokarst lake in the permafrost–dominated region on the Qinghai–Tibet plateau

As a result of global warming induced permafrost degradation in recent decades, thermokarst lakes in the Qinghai–Tibet plateau (QTP) have been regulating local hydrological and ecological processes. Simulations with coupled moisture–heat numerical models in the Beiluhe basin (located in the hinterland of permafrost regions on the QTP) have provided insights into the interaction between groundwater flow and the freeze–thaw process. A total of 30 modified SUTRA scenarios were established to examine the effects of hydrodynamic forces, permeability, and climate on thermokarst lakes. The results indicate that the hydrodynamic condition variables regulate the permafrost degradation around the lakes. In case groundwater recharges to the lake, a low–temperature groundwater flow stimulates the expansion of the surrounding thawing regions through thermal convection. The thawing rate of the permafrost underlying the lake intensifies when groundwater is discharged from the lake. Under different permeability conditions, spatiotemporal variations in the active layer thickness significantly influence the occurrence of an open talik at the lake bottom. A warmer and wetter climate will inevitably lead to a sharp decrease in the upper limit of the surrounding permafrost, with a continual decrease in the duration of open talik events. Overall, our results underscore that comprehensive consideration of the relevant hydrologic processes is critical for improving the understanding of environmental and ecological changes in cold environments.     

An Eocene/Oligocene blueschist‐/greenschist facies P–T loop from the Cycladic Blueschist Unit on Naxos Island,Greece: Deformation‐related re‐equilibration vs. thermal relaxation

Geothermobarometric and geochronological work indicates a complete Eocene/early Oligocene blueschist/greenschist facies metamorphic cycle of the Cycladic Blueschist Unit on Naxos Island in the Aegean Sea region. Using the average pressure–temperature (P–T) method of thermocalc coupled with detailed textural work, we separate an early blueschist facies event at 576 ± 16 to 619 ± 32°C and 15.5 ± 0.5 to 16.3 ± 0.9 kbar from a subsequent greenschist facies overprint at 384 ± 30°C and 3.8 ± 1.1 kbar. Multi‐mineral Rb–Sr isochron dating yields crystallization ages for near peak‐pressure blueschist facies assemblages between 40.5 ± 1.0 and 38.3 ± 0.5 Ma. The greenschist facies overprint commonly did not result in complete resetting of age signatures. Maximum ages for the end of greenschist facies reworking, obtained from disequilibrium patterns, cluster near c. 32 Ma, with one sample showing rejuvenation at c. 27 Ma. We conclude that the high‐P rocks from south Naxos were exhumed to upper mid‐crustal levels in the late Eocene and early Oligocene at rates of 7.4 ± 4.6 km/Ma, completing a full blueschist‐/greenschist facies metamorphic cycle soon after subduction within c. 8 Ma. The greenschist facies overprint of the blueschist facies rocks from south Naxos resulted from rapid exhumation and associated deformation/fluid‐controlled metamorphic re‐equilibration, and is unrelated to the strong high‐T metamorphism associated with the Miocene formation of the Naxos migmatite dome. It follows that the Miocene thermal overprint had no impact on rock textures or Sr isotopic signatures, and that the rocks of south Naxos underwent three metamorphic events, one more than hitherto envisaged.     

Transient seepage analysis in zoned anisotropic soils based on the scaled boundary finite‐element method

The scaled boundary finite‐element method, a semi‐analytical computational scheme primarily developed for dynamic stiffness of unbounded domains, is applied to the analysis of unsteady seepage flow problems. This method is based on the finite‐element technology and gains the advantages of the boundary element method as well. Only boundary of the domain is discretized, no fundamental solution is required and singularity problems can be modeled rigorously. Anisotropic and non‐homogeneous materials satisfying similarity are modeled with no additional efforts. In this study, firstly, formulation of the method for the transient seepage flow problems is derived followed by its solution procedures. The accuracy, simplicity and applicability of the method are demonstrated via four numerical examples of transient seepage flow – three of them are available in the literature. Homogenous, non‐homogenous, isotropic and anisotropic material properties are considered to show the versatility of the technique. Excellent agreement with the finite‐element method is observed. The method out‐performs the finite‐element method in modeling singularity points. Copyright © 2014 John Wiley & Sons, Ltd.     

Assessment of flow paths and confluences for saltwater intrusion in a deltaic river network

Saltwater intrusion is a serious issue in estuarine deltas all over the world due to rapid urban sprawl and water shortage. Therefore, detecting the major flow paths or locations at risk of saltwater intrusion in estuarine ecosystems is important for mitigating saltwater intrusion. In this paper, we introduce a centrality index, the betweenness centrality (BC), to address this problem. Using the BC as the weighted attribute of the river network, we identify the critical confluences for saltwater intrusion and detect the preferential flow paths for saltwater intrusion through the least‐cost‐path algorithm from a graph theory approach. Moreover, we analyse the responses of the BC values of confluences calculated in the river network to salinity. Our results show that the major flow paths and critical confluences for saltwater intrusion in a deltaic river network can be represented by the least cost paths and the BC values of confluences, respectively. In addition, a significant positive correlation between the BC values of confluences and salinity is determined in the Pearl River Delta. Changes in the salinity can produce significant variation in the BC values of confluences. Therefore, freshwater can be diverted into these major flow paths and critical confluences to improve river network management under saltwater intrusion. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of forest roads on the hydrological response of a small‐scale mountain watershed in Greece

The effects of land use changes on the ecology and hydrology of natural watersheds have long been debated. However, less attention has been given to the hydrological effects of forest roads. Although less studied, several researchers have claimed that streamflow changes related to forest roads can cause a persistent and pervasive effect on hillslope hydrology and the functioning of the channel system. The main potential direct effects of forest roads on natural watersheds hydrologic response are runoff production on roads surfaces due to reduced infiltration rates, interruption of subsurface flow by road cutslopes and rapid transfer of the produced runoff to the stream network through roadside ditches. The aforementioned effects may significantly modify the total volume and timing of the hillslope flow to the stream network. This study uses detailed field data, spatial data, hydro‐meteorological records, as well as numerical simulation to investigate the effects of forest roads on the hydrological response of a small‐scale mountain experimental watershed, which is situated in the east side of Penteli Mountain, Attica, Greece. The results of this study highlight the possible effects of forest roads on the watersheds hydrological response that may significantly influence direct runoff depths and peak flow rates. It is demonstrated that these effects can be very important in permeable watersheds and that more emphasis should be given on the impact of roads on the watersheds hydrological response. Copyright © 2014 John Wiley & Sons, Ltd.     

Deciphering late Devonian–early Carboniferous P–T–t path of mylonitized garnet-mica schists from Prins Karls Forland,Svalbard

Quartz-in-garnet inclusion barometry integrated with trace element thermometry and calculated phase relations is applied to mylonitized schists of the Pinkie unit cropping out on the island of Prins Karls Forland, western part of the Svalbard Archipelago. This approach combines conventional and novel techniques and allows deciphering of the pressure–temperature (P–T) evolution of mylonitic rocks, for which the P–T conditions could not have been easily deciphered using traditional methods. The results obtained suggest that rocks of the Pinkie unit were metamorphosed under amphibolite facies conditions at 8–10 kbar and 560–630°C and mylonitized at ~500 to 550°C and 9–11 kbar. The P–T results are coupled with in-situ Th–U-total Pb monazite dating, which records amphibolite facies metamorphism at c. 359–355 Ma. This is the very first evidence of late Devonian–early Carboniferous metamorphism in Svalbard and it implies that the Ellesmerian Orogeny on Svalbard was associated with metamorphism up to amphibolite facies conditions. Thus, it can be concluded that the Ellesmerian collision between the Franklinian margin of Laurentia and Pearya and Svalbard caused not only commonly accepted brittle deformation and weak greenschist facies metamorphism, but also a burial and deformation of rock complexes at much greater depths at elevated temperatures.     

Including spatial distribution in a data‐driven rainfall‐runoff model to improve reservoir inflow forecasting in Taiwan

Multi‐step ahead inflow forecasting has a critical role to play in reservoir operation and management in Taiwan during typhoons as statutory legislation requires a minimum of 3‐h warning to be issued before any reservoir releases are made. However, the complex spatial and temporal heterogeneity of typhoon rainfall, coupled with a remote and mountainous physiographic context, makes the development of real‐time rainfall‐runoff models that can accurately predict reservoir inflow several hours ahead of time challenging. Consequently, there is an urgent, operational requirement for models that can enhance reservoir inflow prediction at forecast horizons of more than 3 h. In this paper, we develop a novel semi‐distributed, data‐driven, rainfall‐runoff model for the Shihmen catchment, north Taiwan. A suite of Adaptive Network‐based Fuzzy Inference System solutions is created using various combinations of autoregressive, spatially lumped radar and point‐based rain gauge predictors. Different levels of spatially aggregated radar‐derived rainfall data are used to generate 4, 8 and 12 sub‐catchment input drivers. In general, the semi‐distributed radar rainfall models outperform their less complex counterparts in predictions of reservoir inflow at lead times greater than 3 h. Performance is found to be optimal when spatial aggregation is restricted to four sub‐catchments, with up to 30% improvements in the performance over lumped and point‐based models being evident at 5‐h lead times. The potential benefits of applying semi‐distributed, data‐driven models in reservoir inflow modelling specifically, and hydrological modelling more generally, are thus demonstrated. Copyright © 2012 John Wiley & Sons, Ltd.