Catchments

A recent review of research on phosphorus input to surface waters from agriculture highlights the variability of particulate and dissolved phosphorus contributions to catchments. The input varies with rainfall, fertilizer application rates, the history of the application of the fertilizer, land use, soil type, and between surface and sub-surface water. The balance struck between export of nutrients from the catchment and recipient-water productivity is the primary factor which controls its quality. 

Cleared forest, igneous catchment 1 Dillon and Kirchmer,... 

All of these techniques are available, but have not been well researched in terms of their nutrient removal efficiency. One exception is the recent work on the efficiency of buffer zones, which used figures of 10-15% for nitrogen and 20-30% for phosphorus reduction by wooded buffer zones in a study of the Slapton Tey catchment. 

In all of the techniques which use artificial barriers to surface run-off of nutrients there is a need to consider the influence of land drains. If these are widespread in a catchment a reduction in nitrogen loading to the watercourses will be unlikely, because the nitrogen is predominantly dissolved and runs through the sub-soil to the drains. Phosphorus control by these barriers will be less affected by land drains because the main input of the phosphorus is in the particulate form which would be prevented from running off the surface to the watercourses. 

The Action plans will also include options for controlling nutrient inputs in the upstream catchments of affected stillwaters. These are likely to include reduction of nutrients from both point and diffuse sources and a range of different combinations aimed at reaching the target concentrations of nutrients required to achieve control in the receiving waters. 

Once the options have been clearly defined it will be necessary to carry out a cost-benefit analysis of each option. This has two main objectives. First, the overall cost of the project will need to be assessed to determine whether or not it is financially viable and, second, to ensure that those who will be required to incur expenditure are fully aware of the commitment needed. The financial benefits to users of the waters for recreation, fisheries, navigation, etc., are relatively easy to determine, but monetary valuation of the environmental benefits such as conservation and general amenity will be more difficult to define. As yet this aspect of the cost-benefit analysis has not been fully developed in the UK. Having determined a range of options and costs for eutrophication control in a particular catchment, consultation on the details of the Action plan with all those involved is needed before any plan can be implemented. 

In 1974, the Harmonized Monitoring Programme was set up by the Department of the Environment (DoE). The objective was to provide a network of sites at the lower end of catchments, where water quality data could be collected and analysed in a nationally consistent manner, allowing the loads of materials carried through river catchments into estuaries to be estimated and long-term trends in river quality to be assessed. The complete list of substances to be monitored is diverse and specifies about 115 substances. The pesticides aldrin, dieldrin, y-HCH, heptachlor, p,p -DDT and p,p -DDE are included. Figures 1 and 2 show the downward trend of y-HCH and dieldrin over the past 20 years at the Harmonized Monitoring Sites. This confirms that reductions in environmental concentrations have been achieved, particularly over the past 10 years. 

Atrazine and simazine arose principally as a result of their use in amenity situations but, since their ban for non-agriciiltiiral purposes, concentrations are generally declining. Fiowever, atrazine and simazine still have some agricultural uses (atrazine on maize and simazine on a wide range of crops), so the risk of pollution still exists when these pesticides are applied in either groundwater or surface water drinking water supply catchments. 

Provide catchment trough and routine maintenance to minimize valveplate leakage... 

We put a lot of effort into improving safety by adding protective equipment onto our plants, new and old gas detectors, emergency isolation valves, interlocks, steam curtains, fire insulation, catchment pits for LPG storage tanks, and so on. We also introduced new procedures, such as hazard and operability studies and modification control, or persuaded people to follow old ones, such as permits-to-work and audits. 

Figure 34.7 Design requested by architect - low plume, no splash (note catchment tray), clear of office block...

Bimetallic corrosion in atmospheres is confined to the area of the less noble metal in the vicinity of the bimetallic joint, owing to the high electrolytic resistance of the condensed electrolyte film. Electrolytic resistance considerations limit the effective anodic and cathodic areas to approximately equal size and therefore prevent alleviation of atmospheric galvanic corrosion through strict application of the catchment area principle. 

In all cases where water is used for cooling, but more especially where it is being evaporated, the hardness figure should be obtained from the local water supply authority. Enquiries should also be made as to possible variations in the supply, since many cities draw their water from two or more catchment areas, and the type and quantity of hardness may change. 

Dunne, T. (1979). Sediment yield and land use in tropical catchments. /. Hydrol. 42, 281-300. 

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