Self‐purification in Upland and Lowland Streams     

Ines Heidenwag  Uta Langheinrich  Volker Lüderitz 《洁净——土壤、空气、水》2001,29(1):22-33

Ecological investigations at four streams in Saxony‐Anhalt have shown that there are considerable differences between the self‐purification power of upland and lowland streams. This result is reflected in chemistry and in microbiology. The structure of the bottom substrate mainly influences the degree of self‐purification in connection with rate of flow and flow velocity. The results and differences are demonstrated using the example of Katzsohlbach in the landscape unit “Mittel‐ and Unterharz” and the stream Olbe in the landscape unit “Magdeburger Börde”.  相似文献   

太阳风流界面的成因          下载免费PDF全文

胡友秋  夏利东 《地球物理学报》1996,39(1):1-6

在日心距离１ＡＵ处的高速流的前沿部位，经常观测到厚度≈１０^４ｋｍ的流界面（ｓｔｒｅａｍｉｎｔｅｒｆａｃｅ）：跨过它密度陡降，温度陡增，风速上升，气压和磁场几乎连续．本文从日心距离０．３ＡＵ处一典型高速流的方位剖面出发，采用二维定态ＭＨＤ模型，研究它在日球赤道面内随日心距离的演化．结果表明，流界面系高速流前沿非线性演化的产物．它先于前、后向激波形成，在日心距离１ＡＵ处得到充分发展，且作为高速流前沿的特征结构之一，可一直延伸到１ＡＵ以远的外日球层．  相似文献   

黄河上游的阶地与水系变迁   总被引：23，自引：3，他引：23  

杨达源  王云飞 《地理科学》1996,16(2):137-143

黄河上游于贵德盆地和共和盆地中有７级阶地，再往上游方向存在阶地级数递减的趋势。共和盆地中还有３级古黄河阶地，黄河上游水系是通过一级级河流袭夺相继贯通的，共和盆地与贵德盆地间的黄河古道始于中更新世末期，龙羊峡河段始于６０ｋａ Ｂ．Ｐ．前后，玛多与唐乃亥 间的峡谷河段是２０ｋａ Ｂ．Ｐ．才贯通的。  相似文献   

On the shot-noise streamflow model and its applications     

Konecny  F. 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(4):289-303

In this paper we consider the shot-noise model of streamflow series. We show how design discharge can be obtained by the stochastic intensity of thinned Poisson processes describing the peaks over a threshold. The main result concerns the stationary distribution of peaks. We derive an explicit expression for this limit distribution in terms of its Laplace transform. Approximation formulas are developed making use of the saddle point method for the asymptotic evaluation of contour integrals and the Post-Widder formula for inversion of Laplace transforms. We illustrate this methods on the case of Gamma-distributed shots. The stationary peak distribution is used to approximate the maximum value distribution for larger time intervals.  相似文献   

The system of the Milky Way, LMC and SMC     

Adam Ružčka 《Astrophysics and Space Science》2003,284(2):519-522

A simple sticky-particle numerical model has been developed in order to check whether extended structures of gas created due to the dynamical evolution of the Galaxy and the Magellanic Clouds system can be explained as remnants of a tidal interaction. Influence of dissipative nature of gaseous medium has been taken into account. The most remarkable features are: the Magellanic Stream, the common HI envelope surrounding both the LMC and SMC and the bridge extended between the Clouds. In contrast to previous works of Murai and Fujimoto (1980), Gardiner et al. (1994) and H and Rohlfs (1994) no presumptions were done on the actual galactocentric velocities of the Magellanic Clouds. The mean values of the LMC and SMC velocity vectors obtained from the Hipparcos proper motion measurements (Kroupa and Bastian, 1997) were used in order to verify whether they allow to reproduce the observed HI distribution. Numerical simulations showed that tidal forces are really significant for the evolution of extended structures such as the Magellanic Stream but this approach becomes unsufficient for the internal regions of galaxies where self-gravity and dissipative properties of the gas cannot be neglected. More precise proper motion measurements are urgently needed. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

SEDIMENT YIELD AND HYDROLOGY IN NORTHWESTERN RANGELANDS     

Charles W. Slaughter 《国际泥沙研究》2000,(2)

lINTRODUCTIONRangeandforestlandsofnorthwesternNorthAmericahavebeenutilizedforres0urceextracti0nandproductionsinceinitialhuman0ccupationofthecontinent.Intensive"managed"utilizati0nofec0systemsforspecificbenefitsincludingcattle,sheep,t1sh,w00dandagriculturalpr0ductshasbeenong0ingfornearly0ne-and-haIfcenturies.Intensiveresourceproducti0nhasto0oftenbeenacc0mpaniedbyunwanted"sideeffects"includingacceleratederosion,s0illossandsedimentdeliveredoffsitetod0wnstreamlocati0ns,estuariesandoceanicsin…  相似文献   

Position of the Gulf Stream influences lake nitrate concentrations in SW Ireland     

Eleanor Jennings  Norman Allott 《Aquatic Sciences - Research Across Boundaries》2006,68(4):482-489

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Scale-dependent influences on water quality, habitat, and fish communities in streams of the Kalamazoo River Basin, Michigan (USA)     

Ashley H. Moerke  Gary A. Lamberti 《Aquatic Sciences - Research Across Boundaries》2006,68(2):193-205

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Drainage density changes during rainfall     

D. G. Day 《地球表面变化过程与地形》1978,3(3):319-326

Observations of stream behaviour during rainfall indicate that previous notions of a simple expanding and contracting network need review and refinement. In a small rural catchment near Armidale, N.S.W. changes in flowing stream length during rainfall have been depicted on flow length graphs which indicate a varied network response to similar rainfall amounts. Channel flow phenomena include discontinuous flow, the generation of flow points within the channel and movement of water downslope from saturated depression sources. Localized physical controls have a significant effect on stream growth which is a sensitive indicator of the catchment response to rainfall. During rapid changes in stream length total flowing length and discharge are highly correlated. A model of the pattern of network expansion and contraction involves several phases of flow contraction.  相似文献   

Quantifying groundwater discharge to a small perennial stream in southern Ontario, Canada   总被引：3，自引：0，他引：3  

Edwin E. Cey  David L. Rudolph  Gary W. Parkin  Ramon Aravena 《Journal of Hydrology》1998,210(1-4):21-37

A study of the interaction between groundwater and surface water was undertaken within a small agricultural watershed in southern Ontario, Canada. Groundwater contributions to streamflow were measured along a section of stream during baseflow conditions and during rainfall events. Four techniques were used to estimate the contribution of groundwater to the stream along a 450 m reach (three during baseflow and one during stormflow conditions). Under baseflow conditions, streamflow measurements using the velocity–area technique indicated that the net groundwater flux to the stream during the summer months was 10 ml s⁻¹ m⁻¹. Hydrometric measurements (i.e. hydraulic gradient and hydraulic conductivity) taken using mini-piezometers installed in the sediments beneath the stream resulted in net groundwater flux estimates that were four to five times lower. Seepage meters failed to provide any measurements of water flux into or out of the stream. Therefore, based on these results, the velocity–area technique gives the best estimate of groundwater discharge. Hydrograph separations were conducted using isotopic ratios and electrical conductivity on two large rainfall events with different antecedent moisture conditions in the catchment. Both events showed that pre-event water (generally considered groundwater) dominated streamflow and tile drain flow with 64%–80% of the total discharge contributed by pre-event water. High water table conditions within the catchment resulted in greater stream discharge and a greater contribution of event water in the streamflow than that observed under low water table conditions for similar intensity storm events. The results also showed that differences in riparian zone width, vegetation and surface saturation conditions between the upper and lower catchment can influence the relative magnitude of streamflow response from the two catchment areas.  相似文献