应用景观生态学原理构建城市河道生态护岸

首先分析了传统水工设计中护岸的弊端,然后从景观生态学角度介绍了岸坡生态系统的主要特征、生态护岸的多种功能和景观生态学内涵;介绍了国内外生态护岸的研究现状,提出了城市河道在生态护岸设计中应在保证稳定安全的前提下,坚持生态优先的原则,重视其景观性和亲水性;最后对生态护岸的材料与植物群落的选择进行了分析。旨在探讨河流生态治理的方法,为生态护岸的构建与河流、洪泛区的治理提供一定的思路和参考。     

Assessing the Effects of Alternative Setback Channel Constraint Scenarios Employing a River Meander Migration Model

River channel migration and cutoff events within large river riparian corridors create heterogeneous and biologically diverse landscapes. However, channel stabilization (riprap and levees) impede the formation and maintenance of riparian areas. These impacts can be mitigated by setting channel constraints away from the channel. Using a meander migration model to measure land affected, we examined the relationship between setback distance and riparian and off-channel aquatic habitat formation on a 28-km reach of the Sacramento River, California, USA. We simulated 100 years of channel migration and cutoff events using 11 setback scenarios: 1 with existing riprap and 10 assuming setback constraints from about 0.5 to 4 bankfull channel widths (bankfull width: 235 m) from the channel. The percentage of land reworked by the river in 100 years relative to current (riprap) conditions ranged from 172% for the 100-m constraint setback scenario to 790% for the 800-m scenario. Three basic patterns occur as the setback distance increases due to different migration and cutoff dynamics: complete restriction of cutoffs, partial restriction of cutoffs, and no restriction of cutoffs. Complete cutoff restriction occurred at distances less than about one bankfull channel width (235 m), and no cutoff restriction occurred at distances greater than about three bankfull widths (∼700 m). Managing for point bars alone allows the setbacks to be narrower than managing for cutoffs and aquatic habitat. Results suggest that site-specific “restriction of cutoff” thresholds can be identified to optimize habitat benefits versus cost of acquired land along rivers affected by migration processes.     

VALUE OF WOODY RWER CORRIDORS IN LEVEE PROTECTION ALONG THE MISSOURI RWER IN 19931

ABSTRACT: Following the Midwest flood of 1993, a study was initiated along a 39-mile segment of the Missouri River to determine if there was an association between woody corridors and levee stability. A systematic sample of levee failures revealed that primary levees which did not fail had a significantly wider woody corridor than failed levees. Analysis of the total inventory of failed levees revealed that as the width of the woody corridor decreased, the length of the levee failure increased. Number of levee failures and their severity of damage could be reduced if woody corridors were at least 300 feet wide.     

鄱阳湖天然湖面遥感监测及其与水位关系研究

以1989—2010年鄱阳湖100期(景)Landsat TM/ETM+影像为数据源,对比分析了水体指数法和谱间关系法两种主要的水体提取方法,利用水体指数法提取了天然湖体水面面积,揭示了不同水位下鄱阳湖天然湖体水面的空间扩展过程与特征,建立了汛期与非汛期水面-水位关系模型并确定了相应代表性水位站。结果表明:①在鄱阳湖,水体指数法水体提取精度优于谱间关系法;②受地形影响,不同水位条件下鄱阳湖天然水面的空间扩展特征大致呈"菱形"沿湖岸以顺时针方向(即:北→东→南→西→北)推进;③水位为6~15 m时,鄱阳湖天然湖体水面随水位变化呈线性变化,水面变化显著;而在水位介于15~22 m时,天然湖体水面随水位变化则呈对数变化。基于水面-水位关系模型,确定汛期代表性水位站为星子站、都昌站与吴城站;而非汛期代表性水位站为棠荫站。     

海河下游塘沽段生态堤岸设计导则

针对海河下游塘沽段堤岸现状,提出该河段堤岸设计导则。该导则适用于从城市高密区到城乡结合区、滨河约15～80m宽度范围,便于城市规划人员在具体地块设计中选用并衍生发展。导则内容包括:(1)导引表;(2)9种堤岸和滨水道路断面推荐设计,根据近岸有无防洪缓冲带、近岸道路特征及护岸形式划分;(3)7种推荐护岸做法,如石笼沉排柔性缓坡护岸、连根树桩与截柳杆柔性缓坡护岸等。导则所推荐的亲水型生态堤岸,可兼顾防洪和河流水质改善作用,有效降低堤防高度,提高河滨人居质量。     

MISSOURI RIVER FLOOD OF 1993: ROLE OF WOODY CORRIDOR WIDTH IN LEVEE PROTECTION1

ABSTRACT. We investigated the relationships between levee damage and woody corridor along a 353‐mile segment of the Missouri River in Missouri during the flood of 1993. Results indicated that woody corridors between riverbanks and primary levees played a significant role in the reduction or prevention of flood related damage to levees. Forty‐one percent of levee failures in this segment occurred in areas with no woody corridor, while 74 percent and 83 percent of failures occurred where woody corridor widths were less than 300 feet and less than 500 feet, respectively. Median failure lengths with a woody corridor present were 50.3 percent shorter than median failure lengths with no woody corridor present. Levees without failures had significantly wider median woody corridor widths than levees that failed. Eligibility for the Corps of Engineers levee maintenance program was not a significant factor in the reduction of levee damage. Discontinuities in woody corridors played a role in 27.5 percent of the levee failures in the study segment. Smaller segments of the river valley were studied to determine if geomorphic differences influenced variations in the protective value of woody corridors.     

Pai洲湾‘98决堤情况典型调查

１９９８年８月１日,湖北省嘉鱼县Ｐａｉ洲湾堤失事溃决,造成生大损失。调查表明,受大堤保护的Ｐａｉ洲湾居民防洪意识淡薄,多认为大堤不会失事。溃堤后,区内居民,尤其是溃口附近的一些居民采取的避洪行为不当,致命人员伤亡严重。这些问题在其他受防洪工程的地区同样存在。加强洪水知识和宣传,提高洪水风险区居民的防洪意识,是减轻洪水灾害的主要工作之一。     

THE LEVEE LOVE AFFAIR: A STORMY RELATIONSHIP?1

ABSTRACT: A history of flood control in the United States shows an undying affair with levees. This love affair, however, was put severely to the test by the record flooding in the summer of 1993. About 70 percent of levees in the upper Midwest failed during this time, leading to extensive damage to both farmland and urban areas. Consequently, there were repeated calls to re-assess the nation's floodplain management policies. The report of the Intera-gency Floodplain Management Review Committee is one outcome of this and it forms the basis of this commentary on levees. In many respects, levees are effective flood control measures, being relatively cheap to implement and easy to build. At the same time, levees have negative impacts, affecting the hydrological regime both up and down stream, and often exacerbating flooding in other places. Furthermore, technical weaknesses in design, planning, construction, and maintenance have all contributed to levee failures. While the report recommends changes in floodplain management to address some of these issues, it is difficult to see how these will materialize given the current political, economic, and social climate.     

EFFECTS OF WOODY VEGETATION ON SANDY LEVEE INTEGRITY1

he influence of woody vegetation on the reliability of a sandy levee was investigated using field data in seepage and slope stability analyses. Field data were collected from selected sites within a 10-km segment of a channel levee on the Sacramento River near Elkhorn, California. Root architecture and distribution were determined using the profile-wall method in which root cross sections were exposed in the vertical wall of an excavated trench. Transects running both parallel and perpendicular to the crest of the levee were excavated at six sites. Each site was dominated by different plant species: five sites were adjacent to trees or woody shrubs, while one supported only herbaceous growth. Lateral plant roots were primarily restricted to, and modified, the near-surface soil horizons to a depth of approximately 1 meter. Root area ratios (RARs) did not exceed 2.02 percent and generally decreased exponentially with depth. At depths greater than 20 cm, mean RARs for sites dominated by wood species were not significantly different from the mean RAB for the herbaceous site. No open voids clearly attributable to plant roots were observed. Roots reinforced the levee soil and increased shear resistance in a measurable manner. Infinite slope and circular arc stability analyses were performed on the landward and riverward slopes under different hydraulic loading conditions. Infinite slope analyses indicated increasing root area ratio from 0.01 percent to 1 percent increased the factor of safety from less than one to more than seven. Circular arc analyses indicated that even the lower measured root concentrations sufficed to increase safety factors for arcs with maximum depths of about 1 m from less than one to about 1.2. Our findings suggest that allowing woody shrubs and small trees on levees would provide environmental benefits and would enhance structural integrity without the hazards associated with large trees such as wind-throwing.