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71.
在我国改革开放政策实行较早的广东珠江三角洲地区,我们对地处西南部的新会市进行了为期两年的全面、典型抽样调查。发现全市的耕地面积和播种面积呈下降趋势,单产虽有较大幅度的增长但粮食总产量的增长缓慢,速度低于全市总人口的自然增长率,因此人均粮食产量呈下降趋势。根据建立的灰色GM(1,1)模型预测,新会市2010年人均耕地面积只有0.025hm^2,在“人均4分保命田”之下。因此,本文对该地区作出的粮食及 相似文献
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The relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes. In landscapes containing hillslopes crenulated by alternating topographic noses and hollows, estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows. Hollows act as local traps for a portion of the colluvium transported down hillslopes, and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area. Analysis of colluvial deposits in nine Oregon Coast Range hollows has yielded average colluvial transport rates into the hollows of about 35cm3cm?1yr?1 and average bedrock lowering rates of about 0.07 mm yr?1 for the last 4000 to 15000 yr. These rates are consistent with maximum bedrock exfoliation rates of about 0.09 mm yr?1 calculated from six of the hollows, supporting the interpretation that exfoliation rates limit erosion rates on these slopes. Sediment yield measurements from nine Coast Range streams provide similar basin-wide denudation rates of between 0.05 and 0.08mm yr?1, suggesting an approximate steady-state between sediment production on hillslopes and sediment yield. In addition, modern sediment yields are similar in basins varying in size from 1 to 1500 km2, suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in the landscape. 相似文献
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常德市水文地质及电测深、电测井的资料反映了孔隙水含水层涌水量的大小与含水层厚度、颗粒组分及其结构的多因素的复杂组合──—厚度(M)与视电阻率(ρ_s)的乘积密切相关,据此可预测单井涌水量。 相似文献
76.
Measurements made on the floors of the temporarily-drained Glenfarg and Glenquey Reservoirs indicate that sediments with wet volumes of 63.94 × 103 m3 and 12.64 × 103 m3 were deposited in 56 and 73 years respectively. These figures represent 2.5 per cent and 1.1 per cent losses of original storage capacity. When corrected for water, organic, and diatom skeleton contents, and reservoir trap efficiency inorganic sediment yields of at least 31.3 tonnes km?2 yr?1 and of 9.0 tonnes km?2 yr?1 are suggested. The difference is probably related to contrasts of land use. 相似文献
77.
Xu Zhaoyi 《吉林大学学报(地球科学版)》1986,(3)
文中用不等径的葫芦状毛管网络模型讨论了均质土的重力释水机制,认为重力释水与变动后的潜水位以上原饱水带及与其相联系的支持毛细水带有关;据此定义了给水度。 均质土给水度的大小与重力释水前后包气带的水分分布特征有关。由模型的分析说明,蒸发条件下的初始水分分布特征曲线偏低,造成均质土的重力释水减量,使给水度变小。 相似文献
78.
A DIAGNOSTIC EXPERIMENTAL STUDY OF EFFECTS OF CO_2 ENRICHMENT ON COTTON GROWTH,DEVELOPMENT AND YIELD
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A series of experiments were conducted about the effects of different CO_2 concentrations andventilating time on cotton using OPT-1 open top chambers.The results show that.for all theventilating treatments,the development stages of cotton were advanced,plant height increased,thebiomass of root and stalk increased when CO_2 concentration increased: the number of bolls formed insummer was more than 85% of the total for the treatment of 700 ppm CO_2 concentration; single bollweight,the number of bolls per plant,ginned and unginned cotton weights,and stalk weightincreased obviously when CO_2 concentration increased,but the influences of CO_2 enrichment on theratio of ginned weight to the total weight of ginned and unginned cotton,fibre length and ginnedweight of 100-seed were small. 相似文献
79.
Exposed roots were used to estimate soil and bedrock erosion on the cut slopes of a 45-year-old road constructed in granitic soils of the Idaho Batholith. The original roadcut surface was defined by projecting a straight line from the toe of the cut past the end of the exposed root to the intersection of a straight line projected along the surface of the hillslope. A cross-sectioning technique was then used to determine erosion to the present roadcut surface. A total of 41 exposed root sites were used to estimate erosion on a 1350 m-long section of road. Average erosion was 1·0 and 1·1 cm/year for soil and bedrock respectively. Buttressing by tree roots caused lower erosion rates for soil as compared to bedrock. Both soil and bedrock erosion rates showed statistically significant correlations with the gradients of the original cut slope. The bedrock erosion data provide a reasonable estimate of the disintegration rate of exposed granitic bedrock exhibiting the weathering and fracturing properties common to this area. The road is located in a study watershed where long-term sediment yield data are available. Sediment data from adjacent study watersheds with no roads were compared to sediment data from the roaded watershed to estimate the long-term increase in sediment yield caused by the road. The increase amounts to about 2·4 m3/year. This figure, compared to the average annual on-site road erosion, provides an erosion to sediment delivery ratio of less than 10 per cent. Based on study results, road construction and maintenance practices are suggested for helping reduce roadcut erosion. 相似文献
80.
Boubacar KANE Pierre Y. JULIEN 《国际泥沙研究》2007,22(2):114-119
An extensive database of reservoir sedimentation surveys throughout continental United States is compiled and analyzed to determine specific degradation SD relationships as function of mean annual rainfall R, drainage area A, and watershed slope S. The database contains 1463 field measurements and specific degradation relationships are defined as function of A, R and S. Weak trends and significant variability in the data are noticeable. Specific degradation measurements are log normally distributed with respect to R, A, and S and 95% confidence intervals are determined accordingly. The accuracy of the predictions does not significantly increase as more independent variables are added to the regression analyses. 相似文献