Deteriorated watersheds can be restored: A case study

A project in west-central Colorado demonstrated that a watershed dissected by a dense gully network can be stabilized and rehabilitated. Check dam systems, aided by improved vegetative cover through reduced cattle grazing and plantings, stabilized not only the structurally treated gullies, but also gullies within the network that were not structurally treated. Comparison with untreated gullies located outside of the project area, showed that the outside gullies widened three times as much as the structurally untreated inside gullies. Statistical analysis indicated that precipitation was normal during the treatment and evaluation period.Check dams decreased gully depth by accumulating sediment deposits. In turn, gully bank stabilization was hastened and alluvial aquifer volumes increased. This increase, plus higher infiltration rates as a result of denser vegetation, led to renewed perennial streamflow after 7 treatment years.Within 11 years after treatment, check dam systems and improved vegetation reduced sediment loads in the flows by more than 90 percent, providing a substantial benefit to farmlands and ponds downstream.From this work we are able to conclude that only part of a gully network requires structural treatment. The mainstem gully, and those tributaries controlling the local base levels of others, are the critical segments that should be structurally treated.     

THE IMPACT OF HIGHWAY CONSTRUCTION ON A NORTH FLORIDA WATERSHED1

ABSTRACT A 20 month study of some effects of highway construction on water quality was conducted during construction of Interstate 10 at Tallahassee, Florida. Highway construction resulted in significant increases in turbidity, suspended solids, total phosphorus, and dissolved silicon in downstream waters despite use of recommended procedures for erosion control. Highway construction did not result in significant increases in dissolved phosphorus or nitrogen.     

长江上游区的坡面土壤流失及侵蚀防治

长江上游区的嘉陵江流域、金沙江渡口至屏山河段流域、三峡库区及库周区,土壤坡面流失量都超过3000t/a·km~2,属长江上游流失严重之最,应列为首批治理重点区;三峡区长江主航道及近主航道支流两岸的重力侵蚀十分严重,给长江输入大量难以排除的砂石物质,应重点加强此区域的重力侵蚀防治。最后对此区的水土保持提出了6条意见。     

Land use Systems and Erosion in the Uplands of the Central Coast, Vietnam

Soil erosion is a significant problem in the uplands of the Central Coast, Vietnam. It affects the livelihood of farmers and could hinder the long-term economic development efforts in the uplands. Yet, trapped in poverty, upland farmers, especially the ethnic minority, are still mining the soil using erosive land use systems to meet their urgent needs. This study demonstrates that the level of soil erosion varies across the typical land use systems. The fruit tree-based agroforestry (AF) system is least erosive and most financially profitable. The choice of land use system is influenced by farmers' attributes, land plot characteristics, and policy-related variables. The set of policy variables is important in explaining land use choice by upland farmers. Promoting the switch to AF system and the adoption of soil conservation is of great importance to reducing soil erosion and sustaining development in the uplands. However, it is a very challenging task.     

水土流失灾害防治与黄河经济开发

本文以大量资料和史实,论证了水土流失对工矿、交通、水利、农业等基础工业、基础设施和基础产业的危害;阐明了防治水土流失灾害,是治理黄河的根本,是经济建设的基础,对于黄河流域资源开发具有促进和保障作用。     

A multi-scale coastal vulnerability index: A tool for coastal managers?

Coastal hazard management involves the assessment of vulnerability in natural and human environments. Indices incorporating a diversity of indicators have therefore been used extensively to provide spatial analyses of the degree of vulnerability. Such indices are typically applied at global and national scales, and they involve varying degrees of simplification and aggregation of information. The degree of simplification that is desirable depends on the management scale, and higher resolution is required at the local compared to the global scale. To investigate the implications of spatial scale in depicting coastal hazard risk, coastal vulnerability indices were developed at national (Northern Ireland), local authority and site levels. Variables were separated into three sub-indices: a coastal characteristics sub-index concerned with the resilience and susceptibility of the coast to erosion, a coastal forcing sub-index to characterize the forcing variables contributing to wave-induced erosion and a socio-economic sub-index to assess the infrastructure potentially at risk. The three sub-indices were merged to calculate the overall index, which is portrayed in the form of colour-coded vulnerability maps. While a common tripartite index could be employed at national, regional and local scales, the nature of the data used to quantify many of the variables varies according to the scale of management. Some important local variations in vulnerability are masked by simplifications at the national scale. For some variables more detailed information is available as the spatial resolution of the study increases, while others become obsolete as data are of insufficient resolution to differentiate real variability at more detailed scales. The results highlight the importance of spatial scale in developing indices of vulnerability: while a common index architecture can be applied, the selection of variables must take account of the scale at which the hazard is to be assessed. It is likely that limits on index development will also be imposed by data availability at various scales.     

Political influence on non-cooperative international climate policy

We analyze non-cooperative international climate policy in a setting of political competition by national interest groups. In the first stage, countries decide whether to link their domestic emission permit markets to an international market, which only forms if it is supported by all countries. In the second stage, countries non-cooperatively decide on the number of tradable emission allowances. In both stages, special interest groups try to sway the government in their favor. We find that (i) both the choice of regime and the levels of domestic and global emissions only depend on the aggregate levels of organized stakes in all countries and not on their distribution among individual interest groups and (ii) an increase in lobbying influence by a particular lobby group may backfire by inducing a change towards the lobby group's less preferred regime.     

ESTIMATING EROSION RISKS ASSOCIATED WITH LOGGING AND FOREST ROADS IN NORTHWESTERN CALIFORNIA1

ABSTRACT: Erosion resulting from logging and road building has long been a concern to forest managers and the general public. An objective methodology was developed to estimate erosion risk on forest roads and in harvest areas on private land in northwestern California. It was based on 260 plots sampled from the area harvested under 415 Timber Harvest Plans completed between November 1978 and October 1979. Results confirmed previous findings that most erosion related to forest management occurs on a small fraction of the managed area. Erosion features larger than the minimum size inventories in this study (> 13 yd³) occupied only 0.2 percent of the area investigated. Linear discriminant analysis was used to develop two equations for identifying critical sites (sites with erosion >100 yd³ac^?1). The equations were based on slope, horizontal curvature (an expression of local topography), and soil color (on road sites) or the strength of the underlying rocks (on harvest sites). The equations can be used in planning to estimate the erosion risk of proposed activities. They can also be used to estimate acceptable risk thresholds based on the value of competing resources.     

MODELING UPLAND EROSION1

ABSTRACT: We have developed a computer model of soil loss on an upland watershed from the continuity considerations for sediment transport and from equations describing rill and interrill erosion. The model is based on dividing the upland area into a grid containing rill and interill zones, on the Universal Soil Loss Equation (USLE), and on equations describing detachment and transport capacity of rill flow. The USLE estimates the sediment load from the contributing areas. The location and amount of total erosion and deposition are determined by comparing the transport and detachment capacity of rill flow for specific storms. The model considers the mechanics of erosion process and can serve as basis for reservoir and channel design and land use planning.     

ECONOMIC EVALUATION OF WATERSHED PROJECTS - AN OVERVIEW METHODOLOGY AND APPLICATION1

ABSTRACT: Deforestation and intensive land use on a global scale has resulted in watershed deterioration and threatened municipal and irrigation reservoirs. Watershed rehabilitation programs must allocate funds to priority projects. A tool for decisionmakers is presented which provides a four-step overview economic analysis by the integration of physical and biological considerations. The overview tool is applied to a current proposed watershed project in Morocco.