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201.
Sensitivity of SCS Models to Curve Number Variation1 总被引:1,自引:0,他引:1
Timothy R. Bondelid Richard H. McCuen Thomas J. Jackson 《Journal of the American Water Resources Association》1982,18(1):111-116
ABSTRACT: The Soil Conservation Service (SCS) models, including the TR-20 computer program and the simplified methods in TR-55, are widely used in hydrologic design. The runoff curve number (CN), which is an important input parameter to SCS models, is defined in terms of land use tretments, hydrologic, condition, antecedent soil moisture, and soil type. The objective of this study was to evaluate the sensitivity of the SCS models to errors in CN estimates. The results show that the effects of CN variation decrease as the design rainfall depth increases, such as for the larger storm events. The value and use of the sensitivity curves are demonstrated using a comparison of Landsat and conventionally derived curve numbers for three watersheds in Pennsylvania. 相似文献
202.
Timothy O'Riordan 《The Environmentalist》1981,1(1):15-24
Summary Environmental management is defined as a mechanism for alleviating the worst of environmental damage and reducing the most unacceptable aspects of social inequalities but without really altering the patterns of political and economic power. It is now increasingly regarded as accepted practice in development partly because it is economically and socially counterproductive to ignore it. The purpose of the paper is to illustrate the difficulties involved in incorporating environmental management into economic growth with special reference to development assistance. Much environmental damage in the Third World is a product of the forces of development rather than the fault of the people, and in the past development assistance projects have often inadvertently led to environmental destruction and social distress. Case examples are given. The paper argues that among the many impediments to the full incorporation of environmental management into development are the following: the administrative structure of the agencies involved, suspicions in the past of receiving nation governments and the risky nature, and expensive labour intensity of programmes aimed at integrated rural development and appropriate technology. Some recommendations are advanced involving administrative reorganisation, new training skills and diplomacy, although no major breakthroughs are expected to come quickly.Geography graduate from the University of Edinburgh, Harkness Fellowship and Carnegie Scholarship to study at Cambridge (UK) and Cornell (USA). University appointments in Canada and UK. Authority in the field of Resource Management. Author of Progress in Resource Management and Environmental Planning. 相似文献
203.
David B. Baker R. Peter Richards Timothy T. Loftus Jack W. Kramer 《Journal of the American Water Resources Association》2004,40(2):503-522
ABSTRACT: The term flashiness reflects the frequency and rapidity of short term changes in streamflow, especially during runoff events. Flashiness is an important component of a stream's hydrologic regime. A variety of land use and land management changes may lead to increased or decreased flashiness, often to the detriment of aquatic life. This paper presents a newly developed flashiness index, which is based on mean daily flows. The index is calculated by dividing the pathlength of flow oscillations for a time interval (i.e., the sum of the absolute values of day‐to‐day changes in mean daily flow) by total discharge during that time interval. This index has low interannual variability, relative to most flow regime indicators, and thus greater power to detect trends. Index values were calculated for 515 Midwestern streams for the 27‐year period from 1975 through 2001. Statistically significant increases were present in 22 percent of the streams, primarily in the eastern portion of the study area, while decreases were present in 9 percent, primarily in the western portion. Index values tend to decrease with increasing watershed area and with increasing unit area ground water inputs. Area compensated index values often shift at ecoregion boundaries. Potential index applications include evaluation of programs to restore more natural flow regimes. 相似文献
204.
Arturo A. Keller Yi Zheng Timothy H. Robinson 《Journal of the American Water Resources Association》2004,40(3):721-735
ABSTRACT: Traditional approaches to establishing critical water quality conditions, based on statistical analysis of low flow conditions and expressed as a recurrence interval for low flow conditions (e.g., 7Q10), may be inappropriate for drier watersheds. The use of 7Q10 as a standard design flow assumes year‐round flow, but in these watersheds, 7Q10 is zero or very small. In addition, the increasing use of multiple year dynamic water quality models at daily time steps can supercede the use of steady state approaches. Many of these watersheds are also under increasing urbanization pressure, which accentuates the flashiness of runoff and the episodic nature of critical water quality conditions. To illustrate, the conditions in the Santa Clara River, California, are considered. A statistical analysis indicates that higher inorganic nitrogen concentrations correlate strongly with low flow. However, peaks in concentrations can occur during the first storms, particularly where nonpoint source contribution is significant. Critical conditions can thus occur at different flow regimes depending on the relative magnitude of flow and pollutant contributions from various sources. The use of steady state models for these dry semi‐urbanized watersheds based on 7Q10 flows is thus unlikely to accurately simulate the potential for exceeding water quality objectives. Dynamic simulation of water quality is necessary, and as the recent intense storm event sampling data indicate, the models should be formulated to consider even smaller time steps. This places increasing demand on computational resources and datasets to accurately calibrate the models at this temporal resolution. 相似文献
205.
Aquatic toxicity due to the creation and mobilization of chemical constituents by fire has been little studied, despite reports of post-fire fish kills attributed to unspecified pyrogenic toxicants. We examined releases of cyanides from biomass burning and their effect on surface runoff water. In laboratory test burns, available cyanide concentrations in leachate from residual ash were much higher than in leachate from partially burned and unburned fuel and were similar to or higher than the 96-h median lethal concentration (LC50) for rainbow trout (45 microg/l). Free cyanide concentrations in stormwater runoff collected after a wildfire in North Carolina averaged 49 microg/l, again similar to the rainbow trout LC50 and an order of magnitude higher than in samples from an adjacent unburned area. Pyrogenic cyanide inputs, together with other fire-related stressors, may contribute to post-fire fish mortalities, particularly those affecting salmonids. 相似文献
206.
Realizing the benefits of environment, health, and safety (EHS) management systems requires more than just rewriting policies and procedures, EHS tasks and activities must be pushed out into all aspects of the organization. The success of this process necessitates an evolving role for EHS managers. For EHS managers, business integration involves the challenge of integrating environment, health, and safety awareness, responsibility, and action into multiple jobs and business processes, leveraging scarce resources to maximize value and minimize costs. Drawing on recent work in the fields of sociology and political science, this article presents conceptual tools for assisting EHS managers to plan and strategize the changing role of the EHS function. By assessing political opportunities, mobilizing structures, and framing processes, EHS managers can maximize the success of EHS programs, while adding value to companies' core operations. 相似文献
207.
Lizanne Avon Timothy J. Durbin 《Journal of the American Water Resources Association》1994,30(1):99-111
AESTRACT An evaluation of the Maxey-Eakin method for calculating recharge to ground-water basins in Nevada was performed. The evaluation consisted of comparing Maxey-Eakin estimates with independent estimates of recharge, and analyzing the nature of the differences between the groups of estimates. In the comparison with the Maxey-Eakin estimates, two different groups of independent estimates were used: (1) 40 recharge estimates that were identified from water budgets contained in reports by the Nevada Department of Conservation and Natural Resources and (2) 27 recharge estimates that were identified from previous studies that used models. The results of the comparisons indicate generally good agreement between the Maxey-Eakin estimates and both groups of independent estimates. To quantify this agreement, an analysis was conducted to estimate the uncertainty in the Maxey-Eakin method. The analysis produced an upper bound on the standard deviation of the Maxey-Eakin estimate for a given basin. For the group of 40 water-budget estimates, the upper bound on the standard deviation for an individual basin is 4,800 acre-ft/yr, and the corresponding coefficient of variation of the Maxey-Eakin estimate is no greater than 44 percent. For the group of 27 model estimates, the upper bound on the standard deviation is 4,100 acre-ft/yr, and the corresponding coefficient of variation is no greater than 24 percent. 相似文献
208.
Karen A. Poiani W. Carter. Johnson Timothy G. F. Kittel 《Journal of the American Water Resources Association》1995,31(2):283-294
ABSTRACT: We assessed the potential effects of increased temperature and changes in amount and seasonal timing of precipitation on the hydrology and vegetation of a semi-permanent prairie wetland in North Dakota using a spatially-defined, rule-based simulation model. Simulations were run with increased temperatures of 2°C combined with a 10 percent increase or decrease in total growing season precipitation. Changes in precipitation were applied either evenly across all months or to individual seasons (spring, summer, or fall). The response of semi-permanent wetland P1 was relatively similar under most of the seasonal scenarios. A 10 percent increase in total growing season precipitation applied to summer months only, to fall months only, and over all months produced lower water levels compared to those resulting from the current climate due to increased evapotranspiration. Wetland hydrology was most affected by changes in spring precipitation and runoff. Vegetation response was relatively consistent across scenarios. Seven of the eight seasonal scenarios produced drier conditions with no open water and greater vegetation cover compared to those resulting from the current climate. Only when spring precipitation increased did the wetland maintain an extensive open water area (49 percent). Potential changes in climate that affect spring runoff, such as changes to spring precipitation and snow melt, may have the greatest impact on prairie wetland hydrology and vegetation. In addition, relatively small changes in water level during dry years may affect the period of time the wetland contains open water. Emergent vegetation, once it is established, can survive under drier conditions due to its ability to persist in shallow water with fluctuating levels. The model's sensitivity to changes in temperature and seasonal precipitation patterns accentuates the need for accurate regional climate change projections from general circulation models. 相似文献
209.
Elizabeth W. Sulzman Karen A. Poiani Timothy G. F. Kittel 《Environmental management》1995,19(2):197-224
The rapid increase in atmospheric concentrations of greenhouse gases has caused concern because of their potential to alter
the earth's radiation budget and disrupt current climate patterns While there are many uncertainties associated with use of
general circulation models (GCMs), GCMs are currently the best available technology to project changes in climate associated
with elevated gas concentrations. Results indicate increases in global temperature and changes in global precipitation patterns
are likely as a result of doubled CO2.
GCMs are not reliable for use at the regional scale because local scale processes and geography are not taken into account.
Comparison of results from five GCMs in three regions of the United States indicate high variability across regions and among
models depending on season and climate variable. Statistical methods of scaling model output and nesting finer resolution
models in global models are two techniques that may improve projections.
Despite the many limitations in GCMs, they are useful tools to explore climate-earth system dynamics when used in conjunction
with water resource and ecosystem models. A variety of water resource models showed significant alteration of regional hydrology
when run with both GCM-generated and hypothetical climate scenarios, regardless of region or model complexity. Similarly,
ecological models demonstrate the sensitivity of ecosystem production, nutrient dynamics, and distribution to changes in climate
and CO2 levels.
We recommend the use of GCM-based scenarios in conjunction with water resource and ecosystem models to guide environmental
management and policy in a “no-regrets” framework or as part of a precautionary approach to natural resource protection. 相似文献
210.
Ted V. Hromadka Timothy J. Durbin 《Journal of the American Water Resources Association》1986,22(2):249-255
ABSTRACT: A two-dimensional dam-break model was used to predict the inundated area on an alluvial fan downslope from the Orange County Reservoir. The model is based upon a diffusion form of the continuity and momentum equations for long waves in shallow water, and the governing equation is solved by an explicit numerical scheme. In a comparison with a one-dimensional model, the two-dimensional model predicts a wider inundated area. 相似文献