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21.
Predicting channel patterns 总被引:1,自引:0,他引:1
The proposed distinction between meandering and braided river channel patterns, on the basis of bankfull specific stream power and bed material size, is analysed and rejected. Only by using regime-based estimates of channel widths (rather than actual widths) has discrimination been achieved, and it is argued that this procedure is unacceptable.An alternative is to explore the patterning processes underlying the marked pattern scatter on bankfull stream power/bed material size plots. Of the five sets of patterning processes, large-scale bedform development and stability is seen as especially important for meandering and braiding. For gravel-bed rivers, bedforms developed at around or above bankfull stage appear important for pattern generation, with braiding relating to higher excess shear stress and Froude number. There seems to be an upper threshold to both meandering and braiding which is achieved at extreme discharges and steep gradients, as on steep alluvial fans, rather than for the rivers with available flow data here considered. For sand-bed rivers with greater excess shear stress, the equivalent upper plane bed threshold may occur below bankfull, with bed material mobility and bedform modification occurring over a wider range of sub-bankfull discharges. Sand-bed channel margin outlines appear to be less perturbed by bedform effects than gravel bed planforms, and they may have naturally straight or sinuous planforms. Bedform relief may nevertheless lead to some being designated as braided when viewed at low flows.It is concluded that the use of a single-stage stream power measure and bed material size alone is unlikely to achieve meandering/braiding discrimination. 相似文献
22.
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
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24.
黄河上游的阶地与水系变迁 总被引:23,自引:3,他引:23
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
25.
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
26.
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
27.
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
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30.
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