Model prediction capacity of ephemeral gully evolution in conservation tillage systems

Ephemeral gully (EG) erosion has an important impact on agricultural soil losses and increases field surface hydrology connectivity and transport of pollutants to nearby water bodies. Watershed models including an EG component are scarce and not yet properly evaluated. The objective of this study is to evaluate the capacity of one such tool, AnnAGNPS, to simulate the evolution of two EG formed in a conservation tillage system. The dataset for model testing included runoff measurements and EG morphological characteristics during 3 years. Model evaluation focused on EG evolution of volume, width, and length model outputs, and included calibration and testing phases and a global sensitivity analysis (GSA). While the model did not fully reproduce width and length, the model efficiency to simulate EG volume was satisfactory for both calibration and testing phases, supporting the watershed management objectives of the model. GSA revealed that the most sensitive factors were EG depth, critical shear stress, headcut detachment exponent coefficient b, and headcut detachment leading coefficient a. For EG outputs the model was additive, showing low sensitivity to interactions between the inputs. Prediction of EG spatial evolution on conservation tillage systems requires improved development of gully erosion components, since many of the processes were developed originally for traditional tillage practices or larger channel systems. Our results identify the need for future research when EG form within conservation tillage systems, in particular to study gully headcut, soil erodibility, and width functions specific to these practices.     

Climate-change driven increased flood magnitudes and frequency in the British uplands: Geomorphologically informed scientific underpinning for upland flood-risk management

Upland river systems in the UK are predicted to be prone to the effects of increased flood magnitudes and frequency, driven by climate change. It is clear from recent events that some headwater catchments can be very sensitive to large floods, activating the full sediment system, with implications for flood risk management further down the catchment. We provide a 15-year record of detailed morphological change on a 500-m reach of upland gravel-bed river, focusing upon the geomorphic response to an extreme event in 2007, and the recovery in the decade following. Through novel application of two-dimensional (2D) hydrodynamic modelling we evaluate the different energy states of pre- and post-flood morphologies of the river reach, exploring how energy state adjusts with recovery following the event. Following the 2007 flood, morphological adjustments resulted in changes to the shear stress population over the reach, resulting in higher shear stresses. Although the proportion of shear stresses in excess of those experienced using the pre-flood digital elevation model (DEM) varied over the recovery period, they remained substantially in excess of those experienced pre-2007, suggesting that there is still potential for enhanced bedload transport and morphological adjustment within the reach. Although volumetric change calculated from DEM differencing does indicate a reduction in erosion and deposition volumes in the decade following the flood, we argue that the system still has not fully recovered to the pre-flood state. We further argue that Thinhope Burn, and other similarly impacted catchments in upland environments, may not recover under the wet climatic phase currently being experienced. Hence systems like Thinhope Burn will continue to deliver large volumes of sediment further down river catchments, providing new challenges for flood risk management into the future.     

井水位对地壳应力-应变响应灵敏度的研究

从丰镇井水位的潮汐效应、地表水体荷载效应与列车荷载效应分别计算出井水位对各类应力 应变的响应灵敏度,其结果分别是6.6×10-9体应变/mm、9.6×10-7体应变/mm与1.0×10-2体应变/mm;在此基础上,推算出该井水位在张北地震前60mm的缓升型异常相应的含水层应变与应力前兆的量级为5.76×10-5体应变与2.3kPa。     

废弃放射源贮存池的综合地球物理勘查

采用综合地球物理勘查技术,包括高精度磁测、高密度电法和地质雷达(GPR)对某处遗留于地下的铅封放射源进行了系统探查,对所获得的各类异常数据进行了分析处理,并指出了放射源所在的具体空间位置.开挖验证结果与解释结果完全吻合,显示了地球物理勘查技术在环境调查中具有快速、准确和非破坏性的优势.     

片麻岩穹窿与伟晶岩型锂矿的成矿规律探讨

"片麻岩穹窿"是指中下地壳热动力过程产生的与岩浆作用(或混合岩化作用)密切相关的穹状构造,是折返造山的产物.片麻岩穹窿的形成经历了从垂直上升的地壳流导致的岩浆上涌的挤压收缩到岩体侵位的顶部伸展机制的转化过程,这一过程有利于富含锂-铯-钽型(LCT)型伟晶岩的生成和锂族元素的富集.研究表明,位于青藏高原北部的中国松潘-甘孜-甜水海印支造山带是中国大型"伟晶岩型"锂矿资源赋存的基地,松潘-甘孜东南部的超大型甲基卡型伟晶岩型锂矿带,产于具有巴罗式"低/中压-高温"变质组合的三叠纪复理石围岩中,早中生代花岗岩以及衍生的大量含锂稀土矿物的伟晶岩脉侵位有成因关系.研究认为,探究片麻岩穹窿的形成过程和构造成因机制;识别花岗岩-含矿伟晶岩的地球化学属性,揭示花岗岩浆分异作用与含矿伟晶岩相演变的成因联系,以及锂元素迁移、富集熔浆的过程;圈定三叠纪地层中巴罗式变质相带的展布,探明富锂伟晶岩矿带赋存的有利变质相带及形成的P-T条件;揭示"变形-变质-岩浆深熔-成矿"的时空耦合、制约与相互作用,再造造山过程中锂资源富集和保存的规律,以及建立成矿动力学模式;是揭示片麻岩穹窿与伟晶岩型锂矿的成矿规律的重要科学途径.     

北京西郊玉泉山地区岩溶水强径流路径地球物理分析

为研究北京西郊玉泉山地区岩溶水径流路径,需查明区内地层结构和断裂构造发育情况,故在玉泉山周边地区开展了综合地球物理勘查工作。完成1∶25000面积性重力测量3670点,在重力数据解释推断成果基础上,有针对性地布设可控源音频大地电磁测深(CSAMT)剖面测量5.1 km及微动测深点4个。综合研究了基岩起伏形态和构造展布特征,新解释推断了10条可能存在的断裂构造。结合区域水文地质资料,对主要断裂的水文地质意义进行了分析,形成了玉泉山地区岩溶水强径流路径新的认识,部分成果与最新的同位素水化学研究成果一致。本研究为玉泉山泉恢复确定合理的回灌方案提供了地球物理依据。     

综合物探法在小秦岭地区中酸性岩体圈定及空间解析中的应用

蟒岭地区西部地处秦岭腹心,位于不同构造单位结合处,构造变动剧烈,岩浆活动频繁,多数矿产与中酸性岩体息息相关。综合物探工作通过地面高精度磁测、激发极化法和高精度重力测量三种地球物理综合测量方法,开展了研究区的磁场、重力场、极化率和电阻率的分布特征研究。深入分析了地质和地球物理特征的异同,并结合物性工作总结了中酸性岩体与地层的差异,了解了深部隐伏岩体的信息,圈定了岩体在地表的位置,推断出地下深层空间的地质结构,为进一步查找岩体以及其他与之有关的工程勘查活动提供借鉴,为该地区及类似地质背景下隐伏岩体定位预测提供了可靠的方法。     

基于可靠度理论的尾矿坝失稳概率及敏感性分析

为了能够真实反映砭家沟尾矿库的稳定特性,运用Monte Carlo试验原理,考虑库区砂层的空间变异特性,利用Slope/W软件对尾矿库进行了概率分析与敏感性分析。分析表明,抽样方式的不同,使尾矿坝体失稳概率和可靠性指标发生了大幅波动,但是并没有使安全系数产生明显变化,也验证了仅将安全系数作为衡量尾矿坝体稳定性的唯一标准是不合适的;敏感性分析也表明了砂层主要参数对安全系数影响的敏感程度,同时也表明黏聚力是影响库区稳定的主要砂层因素。通过研究,为尾矿库今后的运行与管理提供了理论依据,具有一定的指导意义。     

基于CSA-PLS算法的养殖水体水质快速高光谱预测反演模型研究

养殖水体水质的优劣直接影响养殖对象的成长,准确、快速、全面地掌控养殖水环境的水质参数变化情况具有重要意义。传统的水质指标监测方法都通过人工采样的方式,不仅耗费时间长,且只能体现局部水体情况。针对这些问题,提出了一种乌鸦搜索算法(CSA)结合偏最小二乘回归(PLSR)的高光谱特征波段筛选方法,快速构建回归模型,实现光谱数据的精准预测反演。以连片的养殖小区为研究对象,采集养殖水体样本并拍摄同时期的高光谱影像数据。首先对提取的采样点光谱数据利用多种数据变换方法分别预处理;其次利用这些数据,对水质指标总氮(TN)、氨氮(NH₄⁺-N)、总磷(TP)和化学需氧量(COD)分别构建全波段的SVR和AdaBoost回归模型,同时与提出的CSA-PLS自动筛选波段方法和传统的连续投影算法(SPA)筛选波段后构建的模型进行比较分析;最后根据决定系数(R²)和均方根误差(REMS)选出适合各水质指标的最优模型。从实验结果可以看出,所提波段筛选方法的AdaBoost模型预测结果优于SVR和传统SPA方法提取特征波段后构建的模型,与全波段最优模...     

Characterization of sudden and sustained base flow jump hydrologic behaviour in the humid seasonal tropics of the Panama Canal Watershed

Base flows are important for tropical regions with pronounced dry seasons, which are facing increasing water demands. Base flow generation, however, is one of the most challenging hydrological processes to characterize in the tropics. In many years during the May–December wet season in the Panama Canal Watershed (PCW), base flows in rivers abruptly increase. This increase persists until the start of the December–April dry season. Understanding this unusual base flow jump (BFJ) behaviour is critical to improve water provisioning in the seasonal tropics, especially during droughts and extended dry seasons. This study developed an integrated approach combining piecewise regression on cumulative average base flow and sensitivity analysis to calculate the timing and magnitude of BFJ. Rainfall, forest cover, mean land surface slope, catchment area, and estimated subsurface storage were tested as predictors for the occurrence and magnitude of the BFJs in seven subcatchments of the PCW. Sensitivity analysis on correlated predictors allowed ranking of predictor contributions due to isolated and cross-correlation effects. Correlations between observed BFJs and BFJs predicted by watershed and rainfall-related predictors were 0.92 and 0.65 for BFJ timing and magnitude, respectively. Forest cover was the second most significant predictor after cumulative rainfall for jump magnitude, owing to larger subsurface storage and groundwater recharge in forests than pastures. Catchments in the mountainous eastern PCW always generated larger jumps due to their higher rainfall and greater forest cover than the western PCW catchments. The cross-correlations between predictors contributed to more than 50% of the jump variances. The results demonstrate the importance of rainfall gradient and catchment characteristics in affecting the sudden and sustained BFJs, which can help inform land management decisions intended to enhance water supplies in the tropics. This study underscores the need for more research to further understand the hydrological processes involved in the BFJ phenomenon, including better BFJ models and field characterizations, to help improve tropical ecosystem services under a changing environment.