FLOOD-RUNOFF FORECASTING WITH HEC1F1

HEC1F is a computer program for making short- to medium-term forecasts of uncontrolled flood runoff. The program employs unit hydrographs and hydrologic routing to simulate runoff from a subdivided basin. Estimates of future rainfall can be accommodated. Runoff parameters for gaged headwater subbasins can be estimated (optimized) in real time. Blending of calculated with observed hydrographs can be performed. HEC1F is a component of an on-line software system that includes capability for data acquisition and processing, precipitation analysis, streamflow forecasting, reservoir system analysis, and graphical display of data and simulation results. The conceptual framework for HEC1F is described, and application of the program is illustrated.     

A statistical approach to estimating driver responsibility in two-car crashes

A statistical model is developed relating driver age distributions in one-car and two-car crashes to the probability that both of the drivers in a two-car crash are similarly responsible for the crash as are drivers in a single-car crash. The model is applied to (a) passenger car crashes in the years 1975–1980 involving a driver fatality, compiled in the U.S. Fatal Accident Reporting System (FARS), and (b) all police-reported crashes occurring in North Carolina in 1979, supplied by the North Carolina Highway Safety Research Center. Appropriate national and North Carolina driver license data are used to estimate exposure to potential crashes as a function of driver age. The model is found to provide an adequate fit to observed driver age distribution in two-car crashes for both data sets. The results obtained from this fit to the model equations indicate that for two-car crashes involving a driver fatality, both drivers contribute to the responsibility for the crash in about 40% of cases, but for less severe two-car crashes, only one of the two involved drivers is generally responsible.     

AN EXAMINATION OF RELATIVE PERMEABILITY RELATIONS FOR TWO-PHASE FLOW IN POROUS MEDIA1

ABSTRACT: A key parameter in modeling two-phase flow phenomena is relative permeability. It is important to understand which variables influence relative permeability, especially since so few measurements of relative permeability have been made for typical contaminants at hazardous waste sites. This paper focuses on the effect of five variables on relative permeability: intrinsic permeability, pore-size distribution, viscosity ratio, interfacial tension, and wettability, by critically reviewing previously published relative permeability experiments. The wide variability in the functional relationship between relative permeability and saturation should be considered in attempts to model two-phase flow.     

Louisiana wetland loss: A regional water management approach to the problem

Loss of Louisiana's coastal wetlands has reached catastrophic proportions. The loss rate is approximately 150 km²/yr (100 acres/day) and is increasing exponentially. Total wetland loss since the turn of the century has been almost 0.5 million ha (1.1 million acres) and represents an area larger than Rhode Island. The physical cause of the problem lies in man's attempts to control the Mississippi River's flooding, while enhancing navigation and extracting minerals. Levee systems and control structures confine sediments that once nourished the wetlands to the river channel. As a consequence, the ultimate sediment deposition is in deep Gulf waters off the Louisiana coast. The lack of sediment input to the interdistributary wetlands results in an accretion deficit. Natural and human-induced subsidence exceeds accretion so that the wetlands sink below sea level and convert to water. The solution is to provide a thin veneer of sediment (approximately 0.6 cm/yr; an average of 1450 g m^?2 yr^?1) over the coastal marshes and swamps and thus prevent the submergence of vegetation. The sediment source is the Mississippi River system. Calculations show that 9.2% of the river's annual suspended sediment load would be required to sustain the deltaic plain wetlands. It should be distributed during the six high-water months (December–June) through as disaggregated a network as possible. The problem is one of distribution: how can the maximum acres of marsh be nourished with the least cost? At present, the river is managed through federal policy for the benefit of navigation and flood control. A new policy structure, recognizing the new role for the river-sediment distribution, is recommended.     

PROBABLE MAXIMUM FLOOD ESTIMATION-EASTERN UNITED STATES1

In 1982, the National Weather Service (NWS) published criteria for developing the spatial and temporal precipitation distribution characteristics of Probable Maximum Storms. The criteria, which are intended for use in the United States east of the 105th meridian, involve four variables: (1) location of the storm center, (2) storm-area size, (3) storm orientation, and (4) temporal arrangement of precipitation amounts. A computer program has been developed which applies the NWS criteria to produce hyetographs of spatially-averaged precipitation for a basin, or for each subbasin if the basin is subdividided. The basis and operational characteristics of the program are described, and an application is illustrated in which the program is used in conjunction with a precipitation-runoff simulation program (HEC-1) to compute a Probable Maximum Flood.     

EFFLUENT IRRIGATION OF PARA GRASS: WATER,NITROGEN, AND BIOMASS BUDGETS1

Para grass, irrigated with secondary domestic sewage effluent, showed excellent response for disposal of large amounts of water, effective nitrogen removal, and high production of excellent fodder. This grass is found throughout the tropics and parts of the subtropics. It endures flooding and forms dense, easily maintained stands. This is the first time its use has been reported for effluent irrigation. Water, nitrogen, and biomass budgets over a 17-month period were measured in eight percolate style lysimeters. Under irrigation rates as great as 98 mm/day, five days/week, evapo-transpiration averaged 4.6 mm/day. With nitrogen applications of 130 to 2,600 kg/ha/yr, ≥ 79 percent of applied nitrogen was harvested in the grass; 3 percent percolated; and ≤ 28 percent was denitrified. With the highest effluent irrigation rates, nitrate-nitrogen levels remained below the 10 mg/L maximum recommended for potable water. Crop productivity for full effluent treatments averaged 110 t/ha/yr, dry weight. Maximum calculated crude protein content was 13 percent. No nitrate-nitrogen level in the forage exceeded 0.1 percent.     

Total mercury determination in sand boxes from Montreal

Direct mercury analysis was successfully applied to determine trace levels of total mercury in samples from sand boxes in Montréal (Québec, Canada). Twenty sand boxes were sampled from across the city and divided into two size fractions, a fine fraction (<100 microm) and a whole fraction. The concentrations of mercury ranged from 1.6 to 35 microg Hg kg(-1) dry soil for the fine fraction and from 0.7 to 6 microg Hg kg(-1) dry soil for the whole fraction. The mercury concentrations correlated with the soil organic carbon content (R2= 0.67) in the sand. The ratio of the concentration of mercury in the fine over the whole fraction varied from 2.2 to 18. Using published soil ingestion rates for children, the calculated daily intake values varied from 0 to 0.5 ng Hg kg(-1) bw d(-1) with an estimated oral ingestion of 200 mg of sand and from 0.2 to 4.7 ng Hg kg(-1) bw d(-1) with an ingestion of 1750 mg of sand. None of the sand boxes contain sufficient amounts of mercury so as to exceed the currently accepted daily intake threshold of 0.105 microg Hg kg(-1) bw d(-1) established by Health Canada.     

EIA training courses organized by the centre for environmental management and planning,University of Aberdeen: An analysis of experience

In 1980, the World Health Organization (Regional Office for Europe) invited The Centre for Environmental Management and Planning (CEMP) to organize a two-week training course on Environmental Impact Assessment (EIA) to provide a comprehensive introduction to EIA with emphasis on methods and techniques for impact identification, prediction and assessment. Not suprisingly the topic of environmental health impact assessment was to be a major focus. Since 1980, the course has been held each year at the University of Aberdeen. An analysis of participation in the course during its first five years yields several impressions about the success of this training effort and the ways in which it might be improved.     

The impact of a disused mine on uranium transport in the River Fal, South West England

Unfiltered and filtered (0.45 and 0.2 microm) water samples and sediment samples (sieved to <180 microm and 180-1000 microm) were collected along an approximately 15 km transect of the River Fal, Cornwall, UK, to examine the impact of the disused South Terras uranium mine on the uranium concentrations of the river water and underlying sediments. The uranium concentration of the water samples fluctuated along the river, with the 0.45 microm filtered water showing the largest, seven-fold, difference between minimum (0.19 microg L(-1)) and maximum (1.34 microg L(-1)) concentrations. The historical uranium mine and spoil heaps were not a significant source of uranium to the river water, as water concentrations were low next to the site, but a highly elevated uranium concentration (1000 mg kg(-1)) was found in sediment below an outflow pipe from this mine. Operationally defined "colloidal" (0.2-0.45 microm) and "dissolved" (<0.2 microm) uranium were the predominant forms of the element in the river water (35 and 45% respectively). The uranium concentration in the dissolved phase showed a correlation coefficient of 0.83 (n= 9) with the total cation concentration, suggesting that the uranium concentration in this fraction is directly linked to weathering of rocks and minerals. The observation that weathering is the dominant mechanism delivering uranium to the river water explains the low uranium concentrations in the river water close to South Terras mine, despite the proximity of the spoil heaps, and the maximum uranium concentrations close to a china clay mining area.