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<br />001503 <br /> <br />30.5--3 <br /> <br />~ATER INFORMATION MANAGEMENT SYSTEM HANDBOOK <br /> <br />Perennial Stream or Reach. A stream channel or channel reach having <br />measurable surface discharge more than 80A of the time. <br /> <br />Pore Pressure. The pressure created in the void spaces between soil <br />particles by air and/or water. When a lake shore or stream bank is <br />submerged, the pressure in the pores of the soil mass is equal to the <br />hydrostatic head due to the water elevation (ignoring any velocity <br />effects). A rapid drop in water surface elevation results in a lack of the <br />counter-balancing pressure of the water body. Since the pores drain <br />slowly, the pore pressure is positive (greater) relative to atmospheric <br />pressure and thus may expand the pores and move the soil mass. <br /> <br />Recession. The third of three <br />hydrograph. It represents the <br />falling or lowering segment). <br />is a groundwater recession (or <br />decreasing rate of groundwater <br /> <br />parts of a typical single-peak simple <br />portion which descends from the peak (the <br />The lower portion of the recession segment <br />depletion) curve which represents the <br />inflow. <br /> <br />Recurrence Interval. The average interval of time within which the <br />magnitude y of the event will be equaled or exceeded once. <br /> <br />Representative Station. A gage station which is used to develop a <br />normalized f10w-duration curve for use on hydrologically similar ungaged <br />watersheds. It is the one station among those available which is most <br />similar to the ungaged point(s) of quantification. <br /> <br />Rising. The second of three parts of a typical single-peak simple <br />hydrograph. It represents the portion which ascends from the approach <br />segment to the peak. <br /> <br />Scour. The enlargement of a flow section by the removal of boundary <br />material through the action of the fluid in motion. Its occurrence is <br />during relatively short periods of time (minutes, hours, days, seasons) and <br />may result in no net change in stream reach bed elevation. <br /> <br />Suitable Stations. Gaging stations which are similar to the pOint(s) of <br />quantification in terms of precipitation and flow regulation. <br /> <br />Thalweg. The line of maximum depth in a channel's longitudinal profile. <br /> <br />Tha1weq Channel. The channel within the active channel that is filled at <br />baseflow stage and is composed of the thalweg and the inner berms. <br /> <br />Vegetation Encroachment. The tendency for vegetation to become established <br />in areas normally devold of such occupancy; specifically, perennial <br />vegetation 9rowing within the active channel (for example, on bars or in <br />the thalweg). <br /> <br />1D No.3 <br />8/28/87 <br />