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文章采用基于遗传算法的经典退水曲线对西江上游主要站点枯季日平均流量进行研究,所率定的退水系数经验证精度较好,能够反映所在流域的径流特性。通过退水系数与流域面积、下垫面性质、植被覆盖度、多年平均径流深等流域特征关系的分析,发现退水系数值(1)对降雨和蒸散发的变化不敏感,整体上随流域面积和植被覆盖度的增加而减小;(2)随地形高差和下垫面透水性的下降而减小;(3)对喀斯特岩溶地貌尤其敏感,表现为退水系数值较非岩溶地区偏大;(4)随多年平均径流深的增大而增大,二者具有指数函数关系。退水系数与流域特征因子的这些规律,可为无资料流域水文预报提供思考和借鉴。 相似文献
94.
基于“学籍信息中的家庭地址承载了学生空间位置”这一假设,通过学籍信息收集了湖南省株洲县小学生的家庭地址,借助高德开放平台提供的地理编码和POI搜索服务,获得到了株洲县小学生的空间位置和分布,并基于最短路径分析和高斯型两步移动搜索法分析了株洲县小学教育资源的空间可达性及其特征,尝试为区域教育资源的空间均衡性分析与规划配置提供新的数据源和方法借鉴。结果表明:① 基于学籍地址和地理编码技术能够较准确地获取株洲县小学生的空间分布。② 株洲县小学生就近入学距离的最大值、平均值和中位数分别为11.83 km、2.10 km和1.81 km,就近入学距离小于2.0 km的学生仅占55.46%,为株洲县兼顾公平和效率的教育资源配置工作带来了挑战。③ 株洲县北部城镇地区因学校数量较多,平均就近入学距离较小,教育资源的空间可达性普遍较高,且空间差异小,均衡性好;而东南部的乡村地区,平均就近入学距离较大,教育资源的空间可达性普遍较低,且空间差异大。④ 基于情景分析,在不造成局地生源稳定性问题的前提下,新增3所学校后,东南部地区的平均就近入学距离和教育资源的空间可达性有很大的改善,龙潭镇和龙门镇的平均入学距离由3784 m和3520 m降低到3116 m和2636 m,教育资源的空间可达性分别由0.0492和0.0982提高到0.0762和0.1496。 相似文献
95.
为了研究古尔班通古特沙漠荒漠-绿洲过渡带区域龟裂土立地条件下免灌人工梭梭林生态特征,探讨林分的最佳建植密度,对莫索湾1983—2021年38 a集水造林地初始种植梭梭、梭梭自然更新苗及不同坡位的土壤水分进行了调查,研究了梭梭生长对密度差异的响应,同时分析了各林地土壤水分的变化特征,探讨了梭梭生长与土壤水分的关系,以期为人工梭梭林的营建与可持续性提供科学依据。结果表明:(1) 当梭梭造林密度为6 m×3.5 m时(480 株·hm-2),母树存活率最高。随造林密度增大,母树保存率与梭梭自然更新比逐渐下降;母树保留密度越大的林地,其长势越差、生物量越低;盖度、郁闭度越高的林地,阻碍浅层土壤水分的补给,导致梭梭更新苗长势及生物量越差。(2) 梭梭母树的林木生长与其根部140~280 cm深度土壤含水量之间均呈显著负相关(P<0.05),且主要利用根部140~240 cm土壤水分,对比3个林地可知该层土壤水分含量越高的林地,其母树的长势越好、生物量越高。(3) 当母树保留密度为360株·hm-2(株行距4 m×7 m)时,梭梭长势较好、整体生物量最高,林下植被更为丰富,林地土壤水分条件相对较好。综上所述,在该地区进行集水造林时,保持该密度更有利于免灌人工梭梭林结构稳定、持续发挥防风固沙效益。 相似文献
96.
Despite the known importance of water temperature for river ecosystems, the thermal regime of streams and rivers can be heavily modified by afforestation. Although the nature of the heat budget affecting streams in forested catchments shows high variability in space and time, most of the studies of stream temperature response to afforestation have lacked replication among streams. This study examined the impacts of coniferous forest plantations on stream water temperature at six sites (three forested and three open moorland) in the Yorkshire Dales, northern England. Our aim was to test the hypothesis that afforestation would alter the thermal regime of streams, leading to reduced year‐round thermal variability, and cooler summer/warmer winter water temperatures, relative to streams flowing across open moorland. Data collected from April 2007 to March 2009 showed similar thermal dynamics among all six streams over the study period, although variability in forested streams was markedly lower as expected. Mean and maximum daily water temperatures were significantly higher in open moorland streams for much of the year but while some forested streams were warmer than individual moorland streams during winter months (November to February), there was considerable overlap in water temperature between moorland and forest streams. Most stream temperature records showed evidence of low/no winter flow and freezing. These results contrast with many previous studies that have reported warmer temperatures in forested versus open moorland streams during winter, a finding that most likely reflects site‐specific hydrological, geomorphological and climatological influences on water temperature in addition to afforestation. This study demonstrates the need for replication of hydrological monitoring when examining the effects of basin‐scale management practices and provides further evidence for changes in stream thermal regime following afforestation, a practice that is likely to increase in future due to growing demands for increased forest cover in the UK uplands. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
97.
Hydrology and solute concentrations of two intermittent Mediterranean streams draining two nested catchments were compared. The two catchments were mainly underlain by granitic rocks and different types of sericitic schists. Only the lowland catchment had an alluvial zone and a well‐developed riparian forest. The rainfall–runoff relationship and the correlation between daily flow concentrations showed that hydrological behaviour was similar at both sites during most of the year. However, reverse fluxes were detected during the wetting and drying up periods only in the stream with an alluvial zone. The intermittence in stream flow also had effects on absolute solute concentrations, temporal solute dynamics and streamwater stoichiometry. Streamwater chemistry was not affected by drainage area, except for cations produced mainly by bedrock dissolution (i.e. calcium and magnesium) that increased with increasing catchment size. Differences in the relationship among cations and anions were detected between the two streams, which could be attributed to biogeochemical processes occurring in the alluvial zone. The multivariate model used in this study showed that stoichiometry was more useful than absolute concentrations when analyzing the influence of different lithologies on streamwater chemistry. Such differences were amplified in autumn, likely due to a low hydrological connectivity between the two nested catchments. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
98.
Soil moisture is highly variable both spatially and temporally. It is widely recognized that improving the knowledge and understanding of soil moisture and the processes underpinning its spatial and temporal distribution is critical. This paper addresses the relationship between near‐surface and root zone soil moisture, the way in which they vary spatially and temporally, and the effect of sampling design for determining catchment scale soil moisture dynamics. In this study, catchment scale near‐surface (0–50 mm) and root zone (0–300 mm) soil moisture were monitored over a four‐week period. Measurements of near‐surface soil moisture were recorded at various resolutions, and near‐surface and root zone soil moisture data were also monitored continuously within a network of recording sensors. Catchment average near‐surface soil moisture derived from detailed spatial measurements and continuous observations at fixed points were found to be significantly correlated (r2 = 0·96; P = 0·0063; n = 4). Root zone soil moisture was also found to be highly correlated with catchment average near‐surface, continuously monitored (r2 = 0·81; P < 0·0001; n = 26) and with detailed spatial measurements of near‐surface soil moisture (r2 = 0·84). The weaker relationship observed between near‐surface and root zone soil moisture is considered to be caused by the different responses to rainfall and the different factors controlling soil moisture for the soil depths of 0–50 mm and 0–300 mm. Aspect is considered to be the main factor influencing the spatial and temporal distribution of near‐surface soil moisture, while topography and soil type are considered important for root zone soil moisture. The ability of a limited number of monitoring stations to provide accurate estimates of catchment scale average soil moisture for both near‐surface and root zone is thus demonstrated, as opposed to high resolution spatial measurements. Similarly, the use of near‐surface soil moisture measurements to obtain a reliable estimate of deeper soil moisture levels at the small catchment scale was demonstrated. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
99.
Vegetation changes can significantly affect catchment water balance. It is important to evaluate the effects of vegetation cover change on streamflow as changes in streamflow relate to water security. This study focuses on the use of statistical methods to determine responses in streamflow at seven paired catchments in Australia, New Zealand, and South Africa to vegetation change. The non‐parametric Mann–Kendall test and Pettitt's test were used to identify trends and change points in the annual streamflow records. Statistically significant trends in annual streamflow were detected for most of the treated catchments. It took between 3 and 10 years for a change in vegetation cover to result in significant change in annual streamflow. Presence of the change points in streamflow was associated with changes in the mean, variance, and distribution of annual streamflow. The streamflow in the deforestation catchments increased after the change points, whereas reduction in streamflow was observed in the afforestation catchments. The streamflow response is mainly affected by the climate and underlying vegetation change. Daily flow duration curves (FDCs) for the whole period and pre‐change and post‐change point periods also were analysed to investigate the changes in flow regime. Three types of vegetation change effects on the flow regime have been identified. The relative reductions in most percentile flows are constant in the afforestation catchments. The comparison of trend, change point, and FDC in the annual streamflow from the paired experiments reflects the important role of the vegetation change. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
100.
Understanding the influence of complex interactions among hydrological factors, soil characteristics and biogeochemical functions on nutrient dynamics in overland flow is important for efficiently managing agricultural nonpoint pollution. Experiments were conducted to assess nutrient export from Ultisol soils in the Sunjia catchment, Jiangxi province, southern China, between 2003 and 2005. Four plots were divided into two groups: two peanut plots and two agroforestry (peanut intercropped with citrus) plots. During the study period, we collected water samples for chemical analyses after each rainfall event that generated overland flow to assess nutrient export dynamics. The concentrations of potassium (K) and nitrate‐N (NO3––N) in overland flow were higher during the wetting season (winter and early spring). This reflects the solubility of K and NO3––N, the accumulation of NO3––N during the dry season and an increase in desorption processes and mixing with pre‐event water caused by prolonged contact with soil in areas with long‐duration, low‐intensity rainfall. In contrast, concentrations of total nitrogen (TN) and total phosphorus (TP) were higher during the wet season (late March to early July) and during the dry season (mid‐July to the end of September or early October). This was due to the interaction between specific hydrological regimes, the properties of the Ultisol and particulate transport processes. Variations in nutrient concentrations during storm events further identified that event water was the dominant source of total nitrogen and total phosphorus, and pre‐event water was the dominant source of NO3––N. In addition, the results obtained for the different land uses suggest that agroforestry practices reduce nutrient loss via overland flow. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献