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71.
Most land‐based forestry systems use extensive networks of unsealed tracks to access the timber resource. These tracks are normally drained by constructing cross‐banks, or water bars, across the tracks immediately following logging. Cross‐banks serve three functions in controlling sediment movement within forestry compartments:
- 1. they define the specific catchment area of the snig track (also known as skid trails) so that the overland flow does not develop sufficient energy to cause gullies, and sheet and rill erosion is reduced;
- 2. they induce some sediment deposition as flow velocity reduces at the cross‐bank;
- 3. they redirect overland flow into the adjacent general harvesting area (GHA) so that further sediment deposition may take place.
72.
J.D. Mathews M.P. Sulzer C.A. Tepley R. Bernard J.L. Fellous M. Glass M. Massebeuf S. Ganguly R.M. Harper R.A. Behnke J.C.G. Walker 《Planetary and Space Science》1981,29(3):341-348
The results of simultaneous meteor and Thomson scatter radar wind measurements in the 65–105 km altitude region are presented. The two radars are located in Puerto Rico where the 430-MHz Thomson scatter radar at Arecibo Observatory is employed along with the French (CNET) portable meteor radar which is at a 40-km distance. The two sets of wind measurements compare quite favorably during periods of coincident observation. The meteor radar yields continuous results while the Thomson scatter radar is usable only during daylight hours. The Thomson scatter results, on the other hand, extend down to 65 km altitude and are available with better height and time resolutions than the meteor radar results. The two measurement techniques are therefore complementary. 相似文献
73.
Martin Hassellöv Benny Lyvén Henrik Bengtsson Ragna Jansen David R Turner Ronald Beckett 《Aquatic Geochemistry》2001,7(2):155-171
Two clay-rich coastal sediment samples have been characterised together with three pure clays identified as major components of the sediment samples. The mineralogy of the sediments was determined by X-ray diffraction, and their bulk properties measured (organic carbon content, leachable iron and manganese, surface area and cation exchange capacity). A simple approach is used to model the properties of the sediments from those of their pure clay components. Good agreement is found for cation exchange capacity and specific surface area indicating that the clay minerals are the most important constituents influencing the sediments' surface properties. Particle size distributions were assessed by conventional grain size analysis, and also by Sedimentation Field-Flow Fractionation (SedFFF). These two approaches yield sharply differing size distributions; in particular, conventional grainsize analysis indicates a much greater proportion of submicron particles. Similar results are obtained from analysis of pure clays. The most likely reason for this is artifacts introduced in the unavoidable 1 m prefractionation used for SedFFF. 相似文献
74.
Ocean Science Journal - Abandoned, lost or otherwise discarded fishing gear (ALDFG) is rapidly becoming a major global environmental problem. In the present study, a survey of 390 fishermen... 相似文献
75.