Rainfall urban

A problem of many sewage treatment works in the UK is that urban drainage is included with domestic sewage in the sewage collection systems. The resulting storm-water discharges, at times of heavy rainfall, lead to continuing phosphorus export to the river. Correction of this problem requires considerable investment in separate systems. 

In the eastern United States, acid rain consists of 65% sulfuric acid, 30% nitric acid, and 5% other acids. In the West, windblown alkaline dusts buffer the acidity in rains occurring over many rural areas, whereas in urban areas 80% of the acidity is due to nitric acid (28). Average pH in rainfall over the eastern United States for the period April 1979-March 1980 was less than 5.0, with some areas less than pH 4.2 (29). The lowest annual pH recorded was 3.78 at De Bilt, The Netherlands, in 1967, and the lowest in an individual rainfall was 2.4 at Pitlochry, Scotland, on April li) 1974 (30). 

Table 2 Fate and effects of metals in a stream receiving a point-source of metals (upper part of the table) or diffuse input via urban runoff (lower part of the table). Summary of the expected influence of four different hydrological situations base-flow in a rainy period a flood after a rainy period low-flow after a long period of low rainfall (water scarcity) and a flood produced after this drought. Metal concentration (M) metal retention efficiency (measured on the basis of the nutrient spiraling concept) exposure (dose and duration) bioaccumulation (in fluvial biofilms) and metal sensitivity (of biofihns)...

The second case (Table 2) illustrates a hypothetic urban stream receiving both metals and nutrients mainly via urban runoff. Since urban runoff is directly linked with rainfall episodes, metal inputs and exposure will be variable under base-flow during a rainy period and very low under a situation of water scarcity (low rain and low-flow). In this case, a sudden flow increase after strong rains may cause contrasting effects on water metal transport depending on the previous situation. If previous rains have already washed the metals retained in land and sediments, the... 

The topography of the Ebro River basin determines a Mediterranean climate with continental characteristics in most of the river basin as well as a semi-arid climate in the center of the depression. At the western extreme of the basin (Pyrenees and Iberian mountains), there is an oceanic climate. The central part of the basin is isolated from the oceanic influence because of the surrounding mountains. This results in the increase of the continentality of the climate and the drastic decrease of the rainfall. In the central part of the river basin (Zaragoza, Alcaniz, and Lleida urban areas), aridity is the main climatic characteristic. 

Sulfur, Halogens, and Heavy Metals in Urban Summer Rainfall... 

We have employed two multi-elemental techniques (INAA and ICP-AES) to determine sulphur, halogens and 14 other trace elements in urban summer rainfall. Quality control was assured using NBS reference materials. The overall accuracy and precision of these two methods makes possible the routine analysis of many environmentally important trace elements in acid rain related investigations. Enrichment factor calculations showed that several elements including S, Cu, Zn and Cr were abnormally enriched in the urban atmosphere. A comparison of three separate sites showed a strong gradient of metal deposition from the industrial to the outlaying areas. 

Eighteen targeted elements have been determined in urban summer rainfall. We have demonstrated that INAA and ICP offer a unique combination in determining many environmentally important elements in a totally non-destructive fashion. Unfortunately, the main disadvantage of both techniques is that neither Pb, Cd, Co, B, and to a certain extent Cr, cannot be reliably determined in precipitation. 

The extensive use of lead antiknock additives in gasoline has made lead perhaps the most widely distributed toxic heavy metal in the urban environment and has greatly increased its availability for solution in natural waters. It is important for this reason to know whether its introduction into surface and ground waters by rainfall and runoff will make it available for solution or whether chemical processes will place a safe upper limit on its solubility. 

Experimental. The sediment used in this study was obtained from Colma Creek, at Serramonte Boulevard between El Camino Real and Junipero Serra Boulevard, in the city of Colma, San Mateo County, California. Colma Creek was chosen because its entire course occurs within an area of urbanization, and the sediments are therefore of the type which normally come in contact with lead and other heavy metals. The main sources of lead, atmospheric fallout and rainfall runoff contain particulate matter from automobile exhaust emissions. Several shovels full of the bottom material were placed in a plastic container. In the laboratory, several kilograms of the material were wet-sieved, and the fraction passing through a 200-mesh sieve (particle diameter less than 74 ym) was placed in a 1-liter graduated cylinder containing a 1 M sodium phosphate solution. The silt fraction settles in this medium while the finer clay particles remain suspended. After several hours, this clay suspension was then decanted and a portion of the material saved for X-ray diffraction, as were portions of the sand and silt fractions. 

New awareness of the potential danger to water supplies posed by the use of agricultural chemicals and urban industrial development has also focused attention on the nature of rainfall-runoff and recharge processes and the mobility of various solutes, especially nitrate and pesticides, in shallow systems. Dumping and spills of other potentially toxic materials are also of concern because these chemicals may evenmally reach streams and other public water supplies. A better understanding of hydrologic flow paths and solute sources is required to determine the potential impact of contaminants on water supplies, develop management practices to preserve water quality, and devise remediation plans for sites that are already polluted. 

Because there are no direct applications of PBO to water, the exposure of aquatic organisms to PBO is limited to spray drift at the time of application to adjacent lands and runoff associated with rainfall. Regarding drift the EPA uses a default assumption of 5 a- drift, which is defined as 5% of the actual application rate applied to the entire surface of the water body (pond) on a per acre basis. The compound applied is assumed to be instantaneously at equilibrium within the water column (Urban and Cook, 1%6). In modelling aquatic exposure, the amount of chemical in runoff is also added to the water body (pond) based on historical rainfall data, the properties of the chemical, and other factors. 

Weathering steel data indicated rather constant corrosion rates after 8 year exposures (1967-1975) at marine, urban and rural sites in the eastern U.S. Although this data is limited, it suggests that the corrosion history of this weathering steel alloy must be relatively insensitive to both SO2 concentration and to the pH of rainfall. An alternative explanation is that pollutant levels above some threshold value are sufficient to induce the observed corrosion. Even so, the data do not offer clues as to the pollutant effect. 

Further analysis of the available water shows that the blue water locked up in lakes and reservoirs and green water-rainfall water have become increasingly polluted with human, industrial and agricultural wastes and cosmetic chemicals. Most of Africa s largest rivers are severely fragmented by dams, diversions and canals, leading to the degradation of ecosystems. Rapid urbanization in municipahties adds increased pressure on Water Quality. 

Raw urban wastewater is composed of fresh domestic effluent, the quantity and quality of which vary according to time and space (Fig. 1). Two other factors must be considered in order to explain some specific variations rainfall for unitary sewers, and industrial discharges for all types of sewers. 

The first striking feature of urban storm runoffs is their great variability, with quite different pollution values (loads and concentrations) from site to site [7], This variability is closely linked to the nature of storm events. Indeed, each rainfall is different from the other and induces specific phenomena [8], Nevertheless, average values still stand out, which enables a comparison with wastewater in dry weather conditions (Table 1) [9]. 

For degradation forms to develop, however, it is necessary for reactions to occur that can alter or cause stress in the stone. Delivery of potential reactants to a limestone surface can be by two pathways, wet or dry. Wet deposition occurs when gaseous and particulate pollutants are incorporated into water droplets, falling as rain. This solution is usually acidic natural rainfall having a about pH of about 5.6 due to weak carbonic acid urban rainfall falls as... 

The increasing inorganic-matter content within the upper few centimeters of peat corresponds to a period of rapidly rising population and urbanization of the watershed. Land-development activities associated with urbanization promote erosion by increasing the rainfall/runoff ratio (Lull and Reinhart, 1972) and by increasing stream velocity in channels adapted to lesser flows (Hewlett and Nutter, 1%9). Erosion of soil from the watershed and its transport to the salt marsh was directly observed in the field. 

C Assuming a rainfall with intensity po = lOmmh-1 and a monodisperse raindrop distribution with Dp =4 mm, calculate the mass scavenging coefficients for the model continental, marine, and urban distribution of Chapter 8. 

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