Long-term Hydrologic Monitoring Research Articles

Ensuring water security by reviving selected springs in Kangra region, Himachal Himalaya, India

ABSTRACT In the Himalaya, availability of fresh water is a need of mankind, but due to numerous unsustainable developments, hill peoplesare witnessing scarcity of potable water. Hence, there is an imperative need for continuous monitoring of different water sources of Himalaya along with sustainable groundwater management practices in the highlands. The present study is based on extensive field visits investigating natural and other anthropogenic influences on mountain springs, locally known as “boweris”. In the undertaken study, eleven boweris were identified in the Salol region of Kangra, out of which two were exclusively selected as representative boweris, for their detailed studies and revival during the year 2021–2022. The physio-chemical characteristics (pH, TDS, and Electrical Conductivity) of the collected water samples from the boweris and hand pumps were found to be within the acceptable limits as prescribed by Bureau of Indian standards. The correlation between the pairs of TDS-EC depicted a strong positive relationship in both post-monsoon and pre-monsoon seasons and was found to be 0.94 and 0.99, respectively. Results of the t-test show a statistically significant difference in the mean concentrations of TDS (p = 0.02) and EC (p = 0.01) compared to pH (p = 0.39) with no significant difference at 5% significance level during both the seasons in the studied area. It was evident from the field investigations that the recharge structures constructed are facilitating the local boweris in maintaining the water level during the dry seasons. In the Bhatlahru region, the water level in the boweris rose from 127 to 159 cm, whereas in the Salol region, a rise from 119 to 142 cm was observed. The obtained results support the effectiveness and suitability of the proposed structures for the sustainable water resource management in the lower Himalaya. However, regular and long-term hydrological monitoring of the existing groundwater sources of the Himalaya is required for a better understanding of groundwater dynamics.

Long-term hydrological monitoring of soils in the terraced environment of Cinque Terre (north-western Italy)

Terraced landscapes represent one of the most widespread human-induced/man-made transformations of hilly-mountainous environments. Slope terracing produces peculiar morphologies along with unusual soil textures and stratigraphic features, which in turn strongly influence slope hydrology. The investigation of the hydrological features of terraced soils is of fundamental importance for understanding the hydrological dynamics occurring in these anthropogenic landscapes, especially during rainfall events. To this purpose, the availability of extensive field monitoring data series and of information on subsoil properties and structure is essential. In this study, multi-sensor hydrological data were acquired over a period longer than 2 years in the experimental site of Monterosso al Mare, in the Cinque Terre National Park (Liguria region, Italy), one of the most famous examples of terraced landscape worldwide. Monitoring data were coupled with accurate engineering-geological investigations to achieve the hydro-mechanical characterization of backfill soils and to investigate their hydrological response at both the seasonal and the single rainstorm scale. The results indicated that the coarse-grained, and anthropically remolded texture of the soils favors the rapid infiltration of rainwater, producing sharp changes in both soil volumetric water content and pore water pressure. Furthermore, the pattern of hydrological parameters showed seasonal trends outlined by alternating phases of slow drying and fast wetting. The study outcomes provide useful insights on the short and long-term evolution of hydrological factors operating in agricultural terraces. These findings represent a useful basis for a better understanding of the time-dependent processes that guide water circulation in terraced systems, which have a key role in controlling the occurrence of erosion and landslide processes.

Field performance of the GaugeCam image-based water level measurement system

Image-based stage and discharge measuring systems are among the most promising new non-contact technologies available for long-term hydrological monitoring. This article evaluates and reports the long-term performance of the GaugeCam (www.gaugecam.org) image-based stage measuring system in situ. For this we installed and evaluated the system over several months in a tidal marsh to obtain a good stratification of the measured stages. Our evaluation shows that the GaugeCam system was able to measure within about ±5 mm for a 90% confidence interval over a range of about 1 m in a tidal creek in a remote location of North Carolina, USA. Our results show that the GaugeCam system nearly performed to the desired design of ±3 mm accuracy around 70% of the time. The system uses a dedicated target background for calibration and geometrical perspective correction of images, as well as auto-correction to compensate for camera movement. The correction systems performed well overall, although our results show a ‘croissant-shaped’ mean error (-1 to +4 mm,) varying with water stage. We attribute this to the small, yet present, ‘fish-eye’ effect embedded in images, for which our system did not entirely correct in the tested version, and which might affect all image-based water level measurement systems.

Comprehensive Fracture Model of Reservoir Ice Layers in the Northeastern Cold Region of China

Meteorological and hydrological changes have an important influence on the ice formation mechanism and the detailed structure of ice materials in cold reservoirs, and directly determine the mechanical properties of ice materials. Based on long-term meteorological and hydrological monitoring data, and detailed structural evolution analysis of ice materials, combined with fracture mechanics and energy methods, a comprehensive fracture model of ice materials in cold regions is established. At the same time, the fracture mechanics test results and simulation results of ice materials are compared, and the model is finally optimized accurately to provide theoretical support for the study of the mechanical mechanism of ice materials.

Impact of raised beds on surface runoff and soil loss in Alfisols and Vertisols

Hydrological monitoring is crucial to designing agricultural water management (AWM) interventions. This study characterizes the soil hydraulic properties of Alfisols and Vertisols and develops rainfall-runoff-soil loss relationships through long-term hydrological monitoring. Two types of landform management techniques, i.e., raised bed and flat bed, were followed in three paired watersheds of 2–5 ha, characterized by deep Vertisols, medium deep Vertisols and Alfisols. Surface runoff and soil loss were monitored at the outlet of the respective watersheds for 8–12 years. In addition, 29 infiltration tests were conducted using a tension disc infiltrometer by applying a suction of −150 mm, −100 mm, −50 mm, and −20 mm. Soil macro porosity and hydraulic conductivity in the raised bed landform were found to be almost double those in the flat beds at −50 mm suction head in both the soil types. Saturated hydraulic conductivity was found higher in Alfisols compared to Vertisols; however, less runoff was generated in Vertisols compared to Alfisols. This phenomenon is largely explained by the high water storage capacity of Vertisols. Runoff generated from both the soils was less than 2% of total rainfall (<500 mm) received in dry years. In normal years (600–900 mm), runoff coefficient for Vertisols ranged from 7–11% of total rainfall compared to 16–17% in the case of Alfisols. However, runoff generated from fallow land was 17% in deep Vertisols due to higher soil moisture content and limited available storage compared to the cropped land. The raised bed method reduced surface runoff by 15–20 mm in Alfisols compared to 35–40 mm in Vertisols. Runoff from the raised beds was significantly lower during light and moderate intensity rainfall compared to the flat bed method; however, this difference was not significant during events of high and very high intensity rainfall. In addition, raised beds reduced soil loss by 30–60% compared to flat beds. The results of this study are useful in designing evidence-based AWM strategies under rainfed conditions.

Hydrology under change: long-term annual and seasonal changes in small agricultural catchments in Norway

Abstract In agricultural catchments, hydrological processes are highly linked to particle and nutrient loss and can lead to a degradation of the ecological status of the water. Global warming and land use changes influence the hydrological regime. This effect is especially strong in cold regions. In this study, we used long-term hydrological monitoring data (22–26 years) from small agricultural catchments in Norway. We applied a Mann–Kendall trend and wavelet coherence analysis to detect annual and seasonal changes and to evaluate the coupling between runoff, climate, and water sources. The trend analysis showed a significant increase in the annual and seasonal mean air temperature. In all sites, hydrological changes were more difficult to detect. Discharge increased in autumn and winter, but this trend did not hold for all catchments. We found a strong coherence between discharge and precipitation, between discharge and snow water equivalent and discharge and soil water storage capacity. We detected different hydrological regimes of rain and snow-dominated catchments. The catchments responded differently to changes due to their location and inherent characteristics. Our results highlight the importance of studying local annual and seasonal changes in hydrological regimes to understand the effect of climate and the importance for site-specific management plans.

Modern hydrological and morphological state of the Agrakhan Bay and its adverse changes

The study was based, firstly, on the diverse data collected during field work in 2018 – 2020 in the eastern part of the Terek River delta and long-term hydrological monitoring data on the Roshydromet gauges. Secondly, on a profound comparative analysis of multi-temporal cartographic materials and multiple satellite images, laboratory analysis of water and sediment samples and other research groups’ field data. The performed analysis resulted in unprecedented complex and profound assessment of the contemporary hydrological, morphological and ecological state of the former Agrakhan Bay of the Caspian Sea. The drivers, dependencies and parameters of hydrological and morphological degradation were described; a multi-layer large-scale GIS was created to design multiple illustrations. The performed assessment allowed for development of measures for partial restoration of the hydrological and ecological potential of the former Agrakhan Bay.

Descriptive Analysis of the Performance of a Vegetated Swale through Long-Term Hydrological Monitoring: A Case Study from Coventry, UK

Vegetated swales are a popular sustainable drainage system (SuDS) used in a wide range of environments from urban areas and transport infrastructure, to rural environments, sub-urban and natural catchments. Despite the fact that vegetated swales, also known as grassed swales, have received scientific attention over recent years, especially from a hydrological perspective, there is a need for further research in the field, with long-term monitoring. In addition, vegetated swales introduce further difficulties, such as the biological growth occurring in their surface layer, as well as the biological evolution taking place in them. New developments, such as the implementation of thermal devices within the cross-section of green SuDS for energy saving purposes, require a better understanding of the long-term performance of the surface temperature of swales. This research aims to contribute to a better understanding of these knowledge gaps through a descriptive analysis of a vegetated swale in Ryton, Coventry, UK, under a Cfb Köppen climatic classification and a mixed rural and peri-urban scenario. Precipitation and temperature patterns associated with seasonality effects were identified. Furthermore, a level of biological evolution was described due to the lack of periodical and planned maintenance activities, reporting the presence of both plant species and pollinators. Only one event of flooding was identified during the three hydrological years monitored in this research study, showing a robust performance.

Wetlands in the Athabasca Oil Sands Region: the nexus between wetland hydrological function and resource extraction

Oil sands development within the Athabasca Oil Sands Region (AOSR) has accelerated in recent decades, causing alteration to natural ecosystems including wetlands that perform many vital ecosystem functions such as water and carbon storage. These wetlands comprise more than half of the landscape, and their distribution and local hydrology are the result of interactions among a subhumid climate, topography, and spatially heterogeneous surficial and bedrock geology. Since hydrology plays a fundamental role in wetland ecological functioning and determines wetland sensitivity to human disturbances, the characterization of anthropogenic impacts on wetland hydrology in the AOSR is necessary to assess wetland resilience and to improve current best management practices. As such, this paper reviews the impacts of oil sands development and related disturbances including infrastructure construction, gravel extraction, and land clearing on wetland function in the AOSR. Hydrologic disturbances in wetlands in the AOSR include changes to soil hydrophysical properties that control water table position, the interruption of recharge–discharge patterns, and alteration of micrometeorological conditions; these in turn govern wetland ecological structure and wetland ecosystem processes (e.g., evapotranspiration, nutrient cycling). Given that anthropogenic disturbance can affect natural wetland succession, long-term hydrological monitoring is crucial for predicting the response of these ecosystems to varying levels of human impact.

Hydrologic Changes over 60 Years (1959-2019) in an Old-Growth Bald Cypress Swamp on a Rapidly Developing Landscape by Shawn E. Clem and Michael J. Duever

National Audubon Society’s Corkscrew Swamp Sanctuary (Naples, Florida, USA), an ecological relic of Old Florida, protects the largest remaining old-growth bald cypress swamp in the world. A 60-year record of daily water level measurements revealed substantial changes in Corkscrew Swamp’s hydrology as agricultural and residential development have grown to dominate the landscape surrounding the sanctuary. Between 1959 and 2019, surface water data indicate no decadal change in the timing or magnitude of peak wet season water levels or in the hydroperiods (days inundated per water year) of upland hammock and pine forests or wet prairies. Despite little change in rainfall patterns between the 1960s and 2010s, hydroperiods decreased 29% in marshes, 18% in old-growth bald cypress, and 17% in ponds, with the most notable change occurring between the 1990s and 2000s. Average dry season water level recession rate (decrease in water level over time) was 6.3 mm/d in the 2000s and 5.7 mm/d in the 2010s, 47% and 32% higher, respectively, than those seen in earlier decades. Analyses of groundwater data indicated a similar dry season decline between the 1990s and 2000s to that seen in surface water. Analyses of cumulative hydroperiod in surface and groundwater suggested markedly drier conditions began in the 2006 water year. While causes of the observed hydrologic changes are uncertain, likely interacting causes include reduced upstream wet season surface and groundwater storage, increased residential and agricultural extraction, increased downstream drainage, and increased evapotranspiration rates across the region as more deeply-rooted shrubs and trees replace more shallowly-rooted herbaceous plant communities. We discuss significant implications for plant and animal communities, particularly the historic Corkscrew wood stork colony, and discuss the role of long-term hydrologic monitoring for detecting and documenting ecological change.

Citizen science in hydrological monitoring and ecosystem services management: State of the art and future prospects.

Hydrological monitoring is essential to guide evidence-based decision making necessary for sustainable water resource management and governance. Limited hydrometric datasets and the pressure on long-term hydrological monitoring networks make it paramount to explore alternative methods for data collection. This is particularly the case for low-income countries, where data scarcity is more pronounced, and where conventional monitoring methods are expensive and logistically challenging. Citizen science in hydrological research has recently gained popularity and crowdsourced monitoring is a promising cost-effective approach for data collection. Citizen science also has the potential to enhance knowledge co-creation and science-based evidence that underpins the governance and management of water resources. This paper provides a comprehensive review on citizen science and crowdsourced data collection within the context of hydrology, based on a synthesis of 71 articles from 2001 to 2018. Application of citizen science in hydrology is increasing in number and breadth, generating a plethora of scientific data. Citizen science approaches differ in scale, scope and degree of citizen involvement. Most of the programs are found in North America and Europe. Participation mostly comprises a contributory citizen science model, which engages citizens in data collection. In order to leverage the full potential of citizen science in knowledge co-generation, future citizen science projects in hydrology could benefit from more co-created types of projects that establish strong ties between research and public engagement, thereby enhancing the long-term sustainability of monitoring networks.

Relationship between salinity and sonic fish advertisement behavior in a managed sub-tropical estuary: Making the case for an acoustic indicator species

The Florida Everglades have been subjected to decades of human disturbance directly and indirectly related to freshwater management. As a result, intensive efforts directed at restoring water quality in the region have been congressionally mandated. Long-term hydrological monitoring of the Florida Bay Estuary has significantly improved scientific understanding of physical environmental processes within the southern portion of Everglades National Park. Linking environmental processes to ecosystem dynamics, however, requires a relevant metric of biological activity that 1) is representative of ecosystem interactions, 2) can be measured at the same temporal and spatial scales of hydrological data collection, and 3) is at sufficient resolution to provide an understanding of organismal, population, and community-level changes. Through changes in physiology, behavior, or ecology, fishes may respond to acute and chronic changes in their habitats. Passive acoustic detection of sonic fishes may provide an opportunity to link physical and ecosystem processes in estuarine systems. Gulf toadfish (Opsanus beta, family Batrachoididae) are a mid-trophic-level species with a widespread distribution throughout Florida Bay and the broader Gulf of Mexico. Advertising males call in both reproductive and agonistic contexts and exhibit high degrees of nest fidelity. As a result, their calls can be reliably used as an indication of animal presence, as well as behavioral state and reproductive condition. By investigating toadfish call occurrence across three hydrological monitoring stations in Florida Bay, we determined that Gulf toadfish have highest probability of acoustic occurrence at sites with lower salinity (Dunn’s test, p < 0.01), and that Gulf toadfish calling significantly changed with variation in salinity regimes at their nesting locations. For every one unit increase in salinity the probability of toadfish acoustic occurrence decreases by 16% (95% C.I. 7%–23%). This study indicated significant behavioral and acoustic heterogeneity over relatively short distances (7–30 km) within Florida Bay, and demonstrates that local environmental conditions are related to calling behavior in addition to seasonal or broader climatic conditions. Given that a great deal is known about the behavior, physiology, and life history of toadfishes, evidence that Gulf toadfish consistently responded to salinity between and within sites lends strong initial support for the use of Gulf toadfish calling behavior as an acoustic indicator of estuary conditions and environmental change in estuaries targeted for ecological restoration.

Runoff generation in mountain catchments: long-term hydrological monitoring in the Rio Vauz Catchment, Italy

Trying to obtain a more detailed understanding of the hydrological functioning of mountain catchments represents an important challenge in the effort of counteracting possible consequences of climate and land use change on water resources availability. Long-term (&gt; 10 years) hydro-meteorological monitoring in small (typically &lt; 10 km2) experimental catchments constitutes a valuable tool to achieve these goal. One of these sites is the Rio Vauz Catchment (1.9 km2), in the Italian Dolomites, that represents an excellent example of long-term snowmelt-dominated catchment in Dolomitic regions. The strong elevation gradient of the Rio Vauz Catchment and the different physiographic properties of its nested subcatchments make this a unique site for investigating fundamental runoff generation mechanisms in mountain headwaters. In this work, we provide a review of physical processes that have been inferred from 12 years of hydrological monitoring in this catchment. We present the available dataset and summarize the main hydrological mechanisms that explain the internal functioning of the Rio Vauz Catchment, primarily focusing on three characterizing hydrological behaviours, namely thresholds, hysteresis and connectivity. The main control on surface and subsurface runoff threshold response is constituted by a combination of soil moisture antecedent conditions, rainfall amount and topography. Changes in hysteresis patterns (clockwise and anti-clockwise loops) between streamflow and soil moisture, water table depth and electrical conductivity were governed by distinct runoff generation processes and rainfall event characteristics. Hillslope-riparian-stream subsurface connectivity was controlled by antecedent wetness conditions and rainfall amount. The composition in environmental tracers (stable isotopes of water and electrical conductivity) in different water sources and the application of tracer-based mixing models helped to distinguish the geographical sources to runoff and to quantify the role of rainfall and snowmelt in streamflow. Finally, we define a perceptual model of runoff generation processes for dry and wet conditions that can be considered representative for many mountain headwater catchments in the world.

Long-term hydrological monitoring in arid-semiarid Almería, SE Spain. What have we learned?

A combination of high temporal variability and spatial heterogeneity of rainfall, soil surfaces, and plant cover is the cause of the complex hydrological response in arid/semiarid regions. Under these premises, long-term monitoring is necessary to capture drivers controlling the response of these areas and to be able to model and predict their reaction. A succinct, up-to-date review of the databases and results produced by two representative micro-catchments in the most arid extreme of Europe, Almería (SE Spain), is presented with the aim to show how the different precipitation patterns, during a 20-year period, influence the hydrological behavior on different lithologies and soil surfaces. The problems encountered about the functioning of these experimental stations, including the generation and maintenance of long-term databases, is also reviewed.

Temporal variations in the potential hydrological performance of extensive green roof systems

Existing literature provides contradictory information about variation in potential green roof hydrological performance over time. This study has evaluated a long-term hydrological monitoring record from a series of extensive green roof test beds to identify long-term evolutions and sub-annual (seasonal) variations in potential hydrological performance. Monitoring of nine differently-configured extensive green roof test beds took place over a period of 6 years in Sheffield, UK.Long-term evolutions and sub-annual trends in maximum potential retention performance were identified through physical monitoring of substrate field capacity over time. An independent evaluation of temporal variations in detention performance was undertaken through the fitting of reservoir-routing model parameters. Aggregation of the resulting retention and detention variations permitted the prediction of extensive green roof hydrological performance in response to a 1-in-30-year 1-h summer design storm for Sheffield, UK, which facilitated the comparison of multi and sub-annual hydrological performance variations.Sub-annual (seasonal) variation was found to be significantly greater than long-term evolution. Potential retention performance increased by up to 12% after 5-years, whilst the maximum sub-annual variation in potential retention was 27%. For vegetated roof configurations, a 4% long-term improvement was observed for detention performance, compared to a maximum 63% sub-annual variation. Consistent long-term reductions in detention performance were observed in unvegetated roof configurations, with a non-standard expanded-clay substrate experiencing a 45% reduction in peak attenuation over 5-years. Conventional roof configurations exhibit stable long-term hydrological performance, but are nonetheless subject to sub-annual variation.

Assessing the impacts of dams and levees on the hydrologic record of the Middle and Lower Mississippi River, USA

The impacts of dams and levees on the long-term (>130 years) discharge record was assessed along a ~1200 km segment of the Mississippi River between St. Louis, Missouri, and Vicksburg, Mississippi. To aid in our evaluation of dam impacts, we used data from the U.S. National Inventory of Dams to calculate the rate of reservoir expansion at five long-term hydrologic monitoring stations along the study segment. We divided the hydrologic record at each station into three periods: (1) a pre-rapid reservoir expansion period; (2) a rapid reservoir expansion period; and (3) a post-rapid reservoir expansion period. We then used three approaches to assess changes in the hydrologic record at each station. Indicators of hydrologic alteration (IHA) and flow duration hydrographs were used to quantify changes in flow conditions between the pre- and post-rapid reservoir expansion periods. Auto-regressive interrupted time series analysis (ARITS) was used to assess trends in maximum annual discharge, mean annual discharge, minimum annual discharge, and standard deviation of daily discharges within a given water year. A one-dimensional HEC-RAS hydraulic model was used to assess the impact of levees on flood flows. Our results revealed that minimum annual discharges and low-flow IHA parameters showed the most significant changes. Additionally, increasing trends in minimum annual discharge during the rapid reservoir expansion period were found at three out of the five hydrologic monitoring stations. These IHA and ARITS results support previous findings consistent with the observation that reservoirs generally have the greatest impacts on low-flow conditions. River segment scale hydraulic modeling revealed levees can modestly increase peak flood discharges, while basin-scale hydrologic modeling assessments by the U.S. Army Corps of Engineers showed that tributary reservoirs reduced peak discharges by a similar magnitude (2 to 30%). This finding suggests that the effects of dams and levees on peak flood discharges are in part offsetting one another along the modeled river segments and likely other substantially leveed segments of the Mississippi River.

The Impact of Hydrological Parameters on Modelling Slope Safety Factor Towards Shallow Landslides: A Case Study from Oltrepò Pavese

Hydrological monitoring of slope susceptible to shallow landslides allows for identifying the triggering conditions of shallow failures and implementing slope stability analysis at site-specific scale. In this work, a case study of a long-term hydrological monitoring in a slope susceptible to shallow landslides of Oltrepo Pavese (Northern Italy) is presented. The triggering mechanism develops in wet seasons (winter and spring) due to the uprise of a perched water table at about 1 m from ground surface, in consequence of the most intense rainfalls (about > 60 mm in 48 h). Unstable conditions (safety factor < 1.0) are correctly modeled on the basis of both water content and pore water pressure, with a better prediction considering hysteresis effects. Safety factor on the basis of water content can correctly assess the triggering conditions for unsaturated and completely saturated soils. It is possible estimating shallow landslides triggering caused by positive pore water pressures only considering this parameter.

From Rain Tanks to Catchments: Use of Low-Impact Development To Address Hydrologic Symptoms of the Urban Stream Syndrome.

Catchment urbanization perturbs the water and sediment budgets of streams, degrades stream health and function, and causes a constellation of flow, water quality, and ecological symptoms collectively known as the urban stream syndrome. Low-impact development (LID) technologies address the hydrologic symptoms of the urban stream syndrome by mimicking natural flow paths and restoring a natural water balance. Over annual time scales, the volumes of stormwater that should be infiltrated and harvested can be estimated from a catchment-scale water-balance given local climate conditions and preurban land cover. For all but the wettest regions of the world, a much larger volume of stormwater runoff should be harvested than infiltrated to maintain stream hydrology in a preurban state. Efforts to prevent or reverse hydrologic symptoms associated with the urban stream syndrome will therefore require: (1) selecting the right mix of LID technologies that provide regionally tailored ratios of stormwater harvesting and infiltration; (2) integrating these LID technologies into next-generation drainage systems; (3) maximizing potential cobenefits including water supply augmentation, flood protection, improved water quality, and urban amenities; and (4) long-term hydrologic monitoring to evaluate the efficacy of LID interventions.

Progress in the study of the Wenchuan earthquake faulting

After the 2008 Wenchuan earthquake, questions as to how earthquakes occur and when the next large earthquake happens have been asked. These questions are involved in the scientific questions which have been unsolved by geologists and geophysicists, for examples, how do faults rupture? How do faults heal in preparation for the next earthquake? The authors are trying to answer these questions by investigating the internal structures of the Wenchuan earthquake fault zone, fault friction behavior and healing process. The principal slip zone of the Wenchuan earthquake was determined by detailed research based on the WFSD-1 core and outcrop investigation. The dynamic weakening and friction behavior of the Wenchuan earthquake fault was analyzed by long-term temperature monitoring. Long-term hydrological monitoring reveals permeability variations in the Wenchuan fault zone which indicate fault healing process. Based on the information obtained, this paper discusses the Wenchuan earthquake faulting process and the above questions. It is confirmed that the Wenchuan earthquake fault zone(the Yingxiu-Beichuan fault zone) was 105~240 m wide and consisted of 5 different units with different fault rocks, where seismic events occurred repeatedly with multiple coseismic fault weakening mechanisms. Coseismic graphitization occurred during the Wenchuan earthquake; the lowest dynamic friction coefficient(0.02) was measured, and for the first time, the signals showing quick fault healing were recorded. These results not only directly answer the key questions that have puzzled geologists and seismophysiccal researchers for decades but also have important significance for improving the seismic faulting theory and understanding the Wenchuan earthquake fault mechanisms, thus providing a theoretical basis for seismic prevention and disaster mitigation.

Why is the Arkavathy River drying? A multiple-hypothesis approach in a data-scarce region

Abstract. Water planning decisions are only as good as our ability to explain historical trends and make reasonable predictions of future water availability. But predicting water availability can be a challenge in rapidly growing regions, where human modifications of land and waterscapes are changing the hydrologic system. Yet, many regions of the world lack the long-term hydrologic monitoring records needed to understand past changes and predict future trends. We investigated this "predictions under change" problem in the data-scarce Thippagondanahalli (TG Halli) catchment of the Arkavathy sub-basin in southern India. Inflows into TG Halli reservoir have declined sharply since the 1970s. The causes of the drying are poorly understood, resulting in misdirected or counter-productive management responses. Five plausible hypotheses that could explain the decline were tested using data from field surveys and secondary sources: (1) changes in rainfall amount, seasonality and intensity; (2) increases in temperature; (3) groundwater extraction; (4) expansion of eucalyptus plantations; and (5) fragmentation of the river channel. Our results suggest that groundwater pumping, expansion of eucalyptus plantations and, to a lesser extent, channel fragmentation are much more likely to have caused the decline in surface flows in the TG Halli catchment than changing climate. The multiple-hypothesis approach presents a systematic way to quantify the relative contributions of proximate anthropogenic and climate drivers to hydrological change. The approach not only makes a meaningful contribution to the policy debate but also helps prioritize and design future research. The approach is a first step to conducting use-inspired socio-hydrologic research in a watershed.