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.     

活动断层及其避让距离研究综述

综述了活动断层及避让距离的有关进展:(1)对活动断层进行了最新总结,并着重给出了工程上避让距离研究所用的活动断层概念;(2)归纳了世界有关国家活动断层避让的规范和专家的有关研究并进行了评价;(3)对断层地表破裂与避让问题进行了总结,指出符合工程避让的断层精确定位和建立工程分类的避让距离研究是今后应攻关的方向,并提出了供参考的研究结果及想法。     

DIQUAT DISTRIBUTION IN WATER AFTER APPLICATION TO SUBMERSED WEEDS1

ABSTRACT: Diquat herbicide and rhodamine WT dye were applied in a lake to three 1.6 ha plots either with a polymer, which reportedly aids in sinking and confinement of aquatic herbicides, or without a polymer. Diquat and dye concentrations were measured at three different depths in the water column within the plots during the first three hours after application to determine vertical distribution of diquat and dye, and in composite samples at fixed distances from the plot up to 168 hours after application to determine movement out of the treated plots. Diquat and dye were homogeneous in the water column when no polymer was used, but were concentrated near the surface when polymer was used. This distribution may have resulted from temperature stratification. Polymer did not affect movement of diquat or dye out of the plots. The half-lives of diquat within the plots were 25 (SE=6.2) hr, 39 (SE=4.3) hr, and 25 (SE=2.0) hr. Forty-six percent of samples collected at the edges of the plots did not contain detectable diquat residues and only 66 percent of those samples with detectable diquat contained greater than the potable water tolerance (10 ppb). Diquat was not found in any samples 168 hours after application 61 m or farther from the edge of the plots. Dye and diquat concentrations were weakly correlated within and outside the plots. Dye half-lives were consistently higher than diquat, which suggests that the herbicide was removed from the water by plants and sediments more rapidly than dye.     

Building contraventions and incidence of flood in the Lagos Metropolis,Nigeria

Frequent floods have led to loss of lives and destruction of property in both coastal and landlocked cities across the globe, particularly where floodplains have been developed without recourse to space standards. This paper investigated the contributions of contravention of building codes to flooding in flood-prone areas in the Lagos metropolis. Global Positioning Systems (GPSs) were used to determine the location and elevation above sea level of 1,025 buildings situated in 211 streets that were prone to flooding. The distance of buildings from drainage channels/the lagoon was determined in ArcGIS 10.2 environment. Findings revealed that building code contravention contributed significantly to flooding (r = 0.926). About 63.5% and 63.3% of sampled buildings contravened building-plot ratio and statutory setbacks from drainage channels/the lagoon, respectively. Proactive urban planning, strict enforcement of building codes and development control regulations are required to reduce flooding and its consequences in cities of developing nations where flooding has become an annual occurrence.     

西昌市强震断裂避让调查研究

本文详细整理国内外关于强震发震断裂地表破裂避让的有关研究成果,结合对汶川大地震现场的考察,提出在编制城市防震减灾规划中考虑断层避让的工作原则和框架.包括应避让的活动断裂定义,避让的条件,避让范围,并应用于编制西昌市防震减灾规划.