ISO 1070-2018 pdf free.Hydrometry一Slope-area method. The slope—area method is most often used to document a flood or very high flow event. The friction slope defined in the flow resistance formulae is approximated by surveying high-water marks on both banks within the measuring reach to determine the change in water surface elevation, determining the velocity heads at each section, and evaluating the loss due to contraction or expansion. The high- water marks should extend upstream of the most upstream cross section and downstream of the most downstream cross section. The high-water marks may consist of drift on banks, wash lines, seed lines on trees, mud lines, and drift in bushes or trees. Each high-water mark should be rated as excellent, good, fair or poor, which will help with interpreting the high-water profile and slope. Mud lines and seed lines on tree trunks or structures typically are excellent high-water marks. Drift and wash lines are usually good, fair or poor depending on the tendency of the stream bank vegetation to bounce back from the forces exerted on it by the flowing water. Care should be exercised in using high-water marks on trees and other obstacles in high-velocity areas because they may be…