Estimating Land Use Impacts on Regional Scale Urban Water Balance and Groundwater Recharge

Anthropogenic activities have exerted increasingly large-scale influences on terrestrial ecological systems from the past century, primarily through agriculture; however, the impact of such changes on the hydrologic cycle is poorly understood. As one of the important land use (LU) in the coastal Dogo Plain of the Seto Inland Sea, Japan, paddy fields have been decreasing with the increase in urbanization in recent decades. As the main source of water in the Dogo Plain, groundwater plays an important role in providing people with fresh water and contributing to stream base flow. The purpose of this study is to analyze the water resource and evaluate the effect of LU change on groundwater table fluctuation in this coastal plain. Firstly, the observations of groundwater table and the investigation of water balance were carried out in this alluvial plain. Then, a distributed four-block three-layer water balance model was employed to analyze the groundwater table fluctuation with response to the change of paddy field area. Moreover, the role of paddy field in recharging groundwater in the basin has been clarified. Results show that groundwater table depends not only on rainfall and discharge from rivers, but also on irrigation water and topology of the study area. The net groundwater recharge was positive in irrigation periods whereas that in non-irrigation periods was nearly equal to zero or negative. The results of this study would be helpful to the urban development policy and land use planning decision.     

太湖流域主要湖泊的水域动态变化

利用GIS和遥感技术对不同时期的地形图和遥感影像数据进行处理,获取3个时期(1971,1988,2002年)的太湖流域主要湖泊的水域面积。结合多种文献资料,对太湖流域主要湖泊的水域面积变化进行了研究,并分析了引起水域面积变化的主要因素。结果表明,1971~2002年期间太湖流域主要湖泊的水域面积减少了188.87 km2;湖泊水域面积减少的主要原因是由于人类活动的影响。在实地调查研究的基础上,对合理利用与保护湖泊水资源的对策进行了探讨。     

基于复杂地基的切割式横缝碾压混凝土重力坝动力响应分析

巴基斯坦东北部旁遮普省和阿扎德查谟克什米尔地区交界的玛尔水电站大坝为碾压混凝土重力坝,其坝基岩性为不同强度的砂岩以及砂岩与泥岩互层,区域构造及地震地质背景复杂。在进行岩体质量分级的基础上,研究了坝体横缝及坝体-坝基接触缝模拟方法,选取玛尔电站10~#—11~#坝段群为研究对象,运用CZM双线性模型模拟坝体接触缝,计算分析了考虑砂岩泥岩互层地基情况下坝体的动位移和动应力分布状况。结果表明,减小横缝切割深度可以有效降低坝体的动力响应,对坝体应力分布和抗震安全有利;若考虑坝基的砂岩泥岩互层分布,坝踵、坝趾各点的动应力差异显著。     

新旧抗震规范下重力坝抗震安全性能分析

结合新修订的《水电工程水工建筑物抗震设计规范》(NB35047-2015)与原来的《水工建筑物抗震设计规范》(DL5073-2000),采用振型分解反应谱法分析了新旧规范下重力坝地震动应力、动位移与动加速度的分布规律。研究结果表明:与采用原规范计算得到的结果相比,采用修订规范后,各坝型基频对应的反应谱放大系数增大,计算出的坝顶动位移有所增大,而坝顶动加速度反应却呈现降低趋势;建基面部位地震动应力反应有所增大;坝头部位的地震动应力反应有所降低;坝头部位以下的上、下游坝面地震动应力有所增大。结论为工程设计人员利用新抗震规范对重力坝进行抗震安全性评价提供了参考。     

确定性地震动空间差异对重力坝地震响应影响研究

针对高坝-地基体系地震响应分析对空间差异地震动场的需求,在波动输入模型基础上引入地震波组合效应提出确定非一致地震动场模型。该模型从地震动场形成的物理机制出发,以模拟确定性地震动空间差异为目标构建非一致地震动场。随后以确定非一致地震动场和波动输入对应地震动场为基础,采用重力坝算例研究确定性地震动空间差异对结构地震响应的影响。结果显示,相对于波动输入模型,确定非一致地震动场模型可在内蕴多点多维地震动相关性基础上模拟地震动的时间滞后、复杂幅值变化、时程形状差异等宏观空间差异特征。与波动输入地震动场相比,确定非一致地震动场引起重力坝坝踵主拉应力峰值增加的算例占比66.4%,引起下游折坡主拉应力峰值增加的算例占比76.7%。在主拉应力峰值平均值方面,确定非一致地震动场引起坝踵和下游折坡处的最大增幅分别为25.3%和46.4%。考虑工程安全,高坝-地基体系的非一致地震响应分析须全面考虑确定性地震动空间差异的影响。     

考虑变量相关的重力坝建基面抗滑稳定可靠度分析

在重力坝建基面抗滑稳定可靠度计算中,抗剪断摩擦系数和凝聚力存在相关关系.考虑变量相关更加符合工程实际情况,计算得到的可靠指标可信度更高.本文介绍了变量相关的概念和处理方法,编制了相应的计算程序,计算了考虑和不考虑变量相关两种工况的抗滑稳定可靠指标.计算结果表明,考虑变量相关后,可靠指标有较大程度的降低.     

长江上游径流对气象要素变化的敏感性分析

选取长江上游8个主要水文站(直门达、石鼓、屏山、高场、北碚、寸滩、武隆、宜昌)控制流域作为子流域,利用其1979—2015年径流及气象数据,采用机器学习方法计算径流对降水与气温变化的敏感性,并与多元线性回归法和Budyko框架法进行对比,分析降水与气温变化对径流变化的贡献。结果表明：1979—2015年8个子流域径流与降水变化趋势整体不显著(p=0.01),气温呈显著上升趋势(p<0.01);径流对降水、气温的敏感性系数均值范围分别为0.37～0.76 mm/mm、-4.77～-33.53 mm/℃;径流对降水、气温的敏感性系数随着干旱指数的增大而减小;在干旱指数大的子流域降水变化对径流变化的影响更大,在干旱指数小的子流域气温变化对径流变化的影响更大。     

参数变化对HEC-HMS模型流域洪水模拟结果的影响

为分析圩院式防洪模式对流域防洪的影响,以秦淮河流域为研究区,构建HEC-HMS水文模拟模型,分析不透水率、允许水深、排涝模数的变化对流域洪峰和洪量模拟结果的影响。研究结果表明:随着流域不透水率从20%增大至70%时,圩垸式防洪模式下流域洪量和洪峰均呈现增大趋势;当圩垸允许水深增大时,圩垸式防洪模式下流域洪量呈递减趋势,而流域洪峰呈递增趋势;随着排涝模数的降低,流域的洪峰和洪量呈递减趋势。研究成果对秦淮河流域及相似流域的HEC-HMS模型洪水模拟及参数设置具有借鉴和指导意义。     

近40年可鲁克湖-托素湖面积变化及影响因素分析

以位于青海省德令哈市境内的可鲁克湖-托素湖为研究对象,利用美国地质调查局自1973年-2013年的多年遥感影像,运用目视解译和改进的归一化差异水体指数方法提取可鲁克湖和托素湖的面积值,分析其变化特征,结合德令哈市的降水、气温、蒸发、径流、农业灌溉耗水资料,对影响湖泊面积变化的因素进行初步探讨。结果表明,可鲁克湖的面积大致保持不变,托素湖的面积自1973年以来呈现先减小又增大的趋势,降水量呈增加趋势,可以认为湖泊面积变化受降水的影响较小,可鲁克湖的面积主要受蒸发、气温和上游巴音河径流量的影响,但其影响存在明显的滞后性。上游农业耗水量是间接影响托素湖面积变化的主要因素,气温的变化通过影响蒸发量和上游冰雪融水间接影响托素湖的面积。     

RESTORING SALMON HABITAT FOR A CHANGING CLIMATE

An important question for salmon restoration efforts in the western USA is ‘How should habitat restoration plans be altered to accommodate climate change effects on stream flow and temperature?’ We developed a decision support process for adapting salmon recovery plans that incorporates (1) local habitat factors limiting salmon recovery, (2) scenarios of climate change effects on stream flow and temperature, (3) the ability of restoration actions to ameliorate climate change effects, and (4) the ability of restoration actions to increase habitat diversity and salmon population resilience. To facilitate the use of this decision support framework, we mapped scenarios of future stream flow and temperature in the Pacific Northwest region and reviewed literature on habitat restoration actions to determine whether they ameliorate a climate change effect or increase life history diversity and salmon resilience. Under the climate change scenarios considered here, summer low flows decrease by 35–75% west of the Cascade Mountains, maximum monthly flows increase by 10–60% across most of the region, and stream temperatures increase between 2 and 6°C by 2070–2099. On the basis of our literature review, we found that restoring floodplain connectivity, restoring stream flow regimes, and re‐aggrading incised channels are most likely to ameliorate stream flow and temperature changes and increase habitat diversity and population resilience. By contrast, most restoration actions focused on in‐stream rehabilitation are unlikely to ameliorate climate change effects. Finally, we illustrate how the decision support process can be used to evaluate whether climate change should alter the types or priority of restoration actions in a salmon habitat restoration plan. Copyright © 2012 John Wiley & Sons, Ltd.