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11.2.2 MeasurementA suitable choice of method of measuring temperature should be made, takinginto account the particular requirements of the structure.NOTE Different applications require different methods of measurement. Surfacetemperature variations over a large area can be determined using infraredtechniques from either an aircraft or satellite. Variation at a point can be monitoredby comparison of multiple passes of the remote sensing apparatus. On a smallerscale or where depth profiles are required, continuous or repetitive measurementsare taken using thermal sensors, such as thermistors, resistance bulbs, thermocouplesand mercury-in-glass thermometers.11.3 Chemical compositionThe chemical composition of the water should be determined at an early stageof the site investigations, with particular attention being paid to potentiallycorrosive elements such as chloride and sulfate ions.Coastal water is normally fully saturated with oxygen at the surface but, if thereis little vertical mixing, the oxygen content decreases with depth. Under normalcircumstances this decrease is unlikely to have a significant effect unlessanaerobic conditions are reached, but the local distribution and seasonalvariation should be taken into account when siting outfalls to dischargeeffluents that could act as reducing agents.

NOTE The important chemical parameters are usually analysed directly or measuredwith selective ion electrodes, either in the field or in the laboratory.11.4 TurbidityThe effects of turbidity and suspended sediment should be taken into account inharbour design, with special reference to sedimentation and maintenancedredging requirements. The effects of turbidity and suspended sediment shouldalso be taken into account when it is planned to abstract water for industrial orutility purposes, particularly with regard to design of intakes, filters and screens.The risk of blockages of water channels and pipes and wear on pumps should beassessed.NOTE 1 Turbidity is usually caused by suspended clay or silt particles, dispersedorganics and micro-organisms. A lower water temperature increases the amount ofsediment that can be transported in suspension due to the viscosity change.