Calculating the sediment flux of the small coastal watersheds: a modification of global equations

Two kinds of regression equations are used to reproduce the sediment flux of the 26 small coastal watersheds in southeastern China. The first kind is the global equations suggested by Milliman and Syvitski(1992), Mulder and Syvitski(1996), Syvitski et al.(2003), and Syvitski and Milliman(2007). The second kind is the modified equations revised by the characteristics of the coastal watersheds, including the drainage area, mean water discharge, and mean sediment discharge. Compared with the observ...     

Flow dynamics at the continental scale: Streamflow correlation and hydrological similarity

Streamflow variability in space and time critically affects anthropic water uses and ecosystem services. Unfortunately, spatiotemporal patterns of flow regimes are often unknown, as discharge measurements are usually recorded at a limited number of hydrometric stations unevenly distributed along river networks. Advances in understanding the physical processes that control the spatial patterns of river flows are therefore necessary to predict water availability at ungauged locations or to extrapolate pointwise streamflow observations. This work explores the use of the spatial correlation of river flows as a metric to quantify the similarity between hydrological responses of two catchments. Following a stochastic framework, 340,000 cross‐correlations between pairs of daily streamflows time series are predicted at a seasonal timescale across the contiguous United States using 413 catchments of the MOPEX dataset. Model predictions of streamflow correlation obtained in absence of run‐off information are successfully used to identify catchment outlets sharing similar discharge dynamics and flow regimes across a broad range of geomorphoclimatic conditions, without relying on calibration. The selection of reference streamgauges based on predicted streamflow correlation generally outperforms the selection based on spatial proximity, especially as the density of available gauged sections decreases. Interestingly, correlated outlets share a broad spectrum of hydrological signatures (mean discharge, flow variability, and recession properties), suggesting that catchments forced by analogous frequency and intensity of effective rainfall events might exhibit common geomorphoecological traits leading to similar hydrological responses. The proposed framework provides a physical basis to assist the regionalization of flow dynamics and to interpret the spatial variability of flow regimes along stream networks.     

Simulated response of an intermittent stream to rainfall frequency patterns

The response of intermittent catchments to rainfall is complex and difficult to model. This study uses the spatially distributed CATchment HYdrology (CATHY) model to explore how the frequency of daily rainfall (λ) can affect the hydrologic regime of intermittent catchments. After a multi-objective calibration and validation of CATHY against experimental measurements of streamflow and groundwater levels in a catchment used as a pasture, the role of λ in affecting streamflow characteristics was explored using different scenarios. With different values of λ for the dry and wet periods of the year, CATHY showed that a series of frequent rainfall events was often associated with incipient streamflow, independent of the season. Activation of streamflow during the wet season was related to multiple factors and was not often associated with the shallow groundwater levels near the outlet of the catchment. The interplay between rainfall depth and intensity acted as the most important factor for the generation of streamflow. Using the difference between accumulated rainfall and evapotranspiration as a measure of wetness, saturated subsurface flow mechanism generated streamflow in simulations with wetness at least three times larger than mean wetness of other simulations. Although groundwater uprise near the outlet did not effectively contribute to streamflow in the initial days of flow, it strongly correlated with the magnitude of the runoff coefficient. Values of λ close or equal to the maximum value in the wet season can sustain the connectivity between groundwater and streamflow in the riparian zone. This connectivity increases the catchment wetness, which consequently results in an increase of the generated streamflow. Our study showed that rainfall regimes characterized by different λ were able to identify distinct flow regimes typical of either intermittent, ephemeral, or nonflowing catchments. Decrease of λ in the wet season is likely associated with a reduction of streamflow, with a shift of flow regime from intermittent to ephemeral or no-flow.     

Modelling the interaction of climate,forest ecosystem,and hydrology to estimate catchment dissolved organic carbon export

The potential for increased loads of dissolved organic carbon (DOC) in streams and rivers is a concern for regulating the water quality in water supply watersheds. With increasing hydroclimatic variability related to global warming and shifts in forest ecosystem community and structure, understanding and predicting the magnitude and variability of watershed supply and transport of DOC over multiple time scales have become important research and management goals. In this study, we use a distributed process‐based ecohydrological model (Regional Hydro‐Ecological Simulation System [RHESSys]) to explore controls and predict streamflow DOC loads in Biscuit Brook. Biscuit Brook is a forested headwater catchment of the Neversink Reservoir, part of the New York City water supply system in the Catskill Mountains. Three different model structures of RHESSys were proposed to explore and evaluate hypotheses addressing how vegetation phenology and hydrologic connectivity between deep groundwater and riparian zones influence streamflow and DOC loads. Model results showed that incorporating dynamic phenology improved model agreement with measured streamflow in spring, summer, and fall and fall DOC concentration, compared with a static phenology. Additionally, the connectivity of deep groundwater flux through riparian zones with dynamic phenology improved streamflow and DOC flux in low flow conditions. Therefore, this study suggests the importance of inter‐annual vegetation phenology and the connectivity of deep groundwater drainage through riparian zones in the hydrology and stream DOC loading in this forested watershed and the ability of process‐based ecohydrological models to simulate these dynamics. The advantage of a process‐based modelling approach is specifically seen in the sensitivity to forest ecosystem dynamics and the interactions of hydroclimate variability with ecosystem processes controlling the supply and distribution of DOC. These models will be useful to evaluate different forest management approaches toward mitigating water quality concerns.     

Gas-generation potential of shales in small and medium-sized basins: a case study from the Xuanhua Basin,north China

Abstract

Small- and medium-sized basins are widely distributed, and some contain commercial gas reservoirs demonstrating their gas-generation potential. The Xuanhua Basin, which is a small-sized coal-bearing basin in north China, includes a promising target for shale-gas exploration in the Xiahuayuan Formation. In this study, we used this basin as a case study to assess the critical geochemical features for small or medium-sized basins to form commercial gas reservoirs. Total organic carbon (TOC) analysis, Rock-Eval pyrolysis, microscopic observation of macerals, vitrinite reflectance measurement and kerogen stable carbon isotope analysis were performed to characterise the organic geochemistry of the Xiahuayuan shales. The original total organic carbon (TOC_o) content and hydrocarbon-generative potential (S_2o) were reconstructed to further evaluate the gas-generation potential of these shales. In addition, geochemical data of shales from other similar-sized basins with gas discoveries were compared. The results showed that the kerogen from the Xiahuayuan Formation is Type III (gas-prone), and macerals are dominated by vitrinite. TOC values showed a strong heterogeneity in the vertical profiles, with most higher than 1.5?wt%. The measured R_o values ranged from 1.4 to 2.0%. However, thermal maturity was not correlated with the present-day burial depth with higher maturity in the wells closest to the diabase intrusion centre. The remaining generation potential (S₂) averaged 0.91?mg HC/g rock, equal to 1.4?cm³ CH₄/g rock, and the average amount of hydrocarbon generated was 4.33?cm³ CH₄/g rock. In small and medium-sized basins, the TOC content of commercially developed gas shales ranged from 0.5 to 2.5?wt%, organic matter was mainly humic (gas-prone), and the burial depth was generally shallow. Biogenic gas reservoirs for commercial exploitation tend to have larger shale thicknesses (120–800?m) than thermogenic gas reservoirs (60–90?m).

1. The Xiahuayuan Formation is a good gas-source rock with gas-prone kerogen type, relatively high TOC values and moderate thermal maturity.

2. The average amount of hydrocarbon generated from the Xiahuayuan shales is about 4.33?cm³ CH₄/g rock, indicating a potential to form a shale gas reservoir.

3. Owing to the influence of diabase intrusions, the Xiahuayuan shales have entered the dry gas window at relatively shallow-buried depths.

4. Small- and medium-sized basins have the potential to generate commercial gas reservoirs with the generated volume mainly a product of the thickness and maturity of black shales.

     

三方交会法在高层建筑物倾斜测量中的应用

针对前方交会法实施高层建筑物倾斜测量具体操作中的实际问题,提出了一种在三方交会情况下,通过增加多余观测,利用间接平差原理来确定点位的坐标平差值的方法。同时,根据三角形性质定理确定交会点位的最优值,评定其点位精度,其精度高于前方交会法,并与小角法倾斜测量结果进行了比较;通过实地测量成果验证了该方法的可靠性。     

基于第二类无奇点根数的改进根数

采用经典Kepler根数描述天体的基本运动方程时,若出现近圆或近赤道情况,将导致一系列的不确定性,即奇点问题。由于导致这类数学奇点的原因是基本根数变量的选择不当,因此有针对性地选择无奇点根数可以解决这一问题。在前人提出的改进的第二类无奇点根数的基础上,给出详细的星历计算和轨道计算推导过程。并且通过摄动运动方程形式分析以及数值计算对改进根数进行了验证。     

Business networks and the competitiveness of small manufacturing firms in Sweden's northern periphery

The establishment of inter-firm networks is a key resource for the competitiveness of small firms. The literature on small firm networking stresses the importance of building a balanced network of regional and extra-regional networks in order to engender optimal levels of firm performance. In peripheral regions, the academic debate is focused on understanding how geographical remoteness affects the spatial orientation of networks of small firms. Based on the analysis of survey responses and financial accounts of 26 small manufacturing firms located in Sweden's northern periphery, the study investigates how the spatial configuration of networks, and particularly their regional and international components, is related to other aspects of the firms, such as geographical location or level of performance. The study shows that increased geographical remoteness tends to promote the establishment of international relations instead of hindering them and that peripheral small firms able to penetrate international markets tend to achieve higher levels of productivity. The subsequent discussion stresses the need to rethink the spatiality of policies promoting small firm networks, from a locally-bound to a more diversified, internationalised one.     

The Changhsingian small foraminifers from the Gyanyima section in southern Tibet, China

The Gyanyima section is located in the Himala-yan Tethys Zone, just south of the Indus-Tsangbo su-ture. The Permian part of the section is made up of grayish to reddish white reefal limestone that yields rich warm-water faunas of Changhsingian age. We recently found highly diversified smaller foraminifers dominated by Colaniella parva in association with the genera Pachyphloia, Frondina, Nodosaria, Robuloides, Geinitzina, Tetrataxis, Tuberitina, Abadehella, Cli-macammina, Dagmarita, Postendothyra, Neoendo-thyra, Globivalvulina, Paraglobivalvulina, Agatham-mina, Multidiscus, and Kamurana. In comparison, fusulinoideans are a minor element of the fauna and include Nankinella, Staffella, Reichelina pulchra, and Codonofusiella?. In addition to these fusulinoideans, a new boultoniid genus is found in the upper part of the section. This form shares some similarities with Codonofusiella and Parananlingella in its un-coiling or loose-coiling tendency in the last volution, but it is distinct from these two boultoniid genera in having a rapidly expanding but fully coiled last half volution.     

An analysis of the balance of operational water discharge using a combined water-intake system

Possibilities of increasing the available water resources of small-river basins using combined water-intake systems are considered. The modern system of water intake, whose balance is supplied at the expense of reduced river flow, remains the main water-intake system. During low-water periods, a compensation water-intake system is used for maintaining the minimum permissible stream flow. The sources of compensation water-intakes are analyzed.