RIVERS Water The volume of water on Earth is estimated to be about 1.36 billion cubic kilometers with: 97% in the oceans 2% in glaciers l% in streams, lakes, ground water, and the atmosphere The Hydrologic Cycle Evaporation: liquid to vapor Transpiration: release of water vapour from plants Condensation: As water vapour rises, it cools and eventually condenses Precipitation: Rain, snow and hail Surface runoff: Sheet wash or channels Percolation: migration from surface down Ground water: Running Water Streams modify their channels Gradient - slope over which the stream flows The ULTIMATE BASE LEVEL is sea level - streams will not erode their base below base level There may be temporary base levels which control the behavior of segments of a stream - a dam, for example Properties of Moving Water Discharge = Width x Depth x Velocity measured in cubic feet/second An increase in discharge will result in an increase in all three parameters -- unless one of more of the parameters has been fixed. Streams carry sediment as part of the SUSPENDED LOAD or as part of the BED LOAD In general, the suspended material is finer than the bed load and is transported faster than the bed load material. As velocity changes, for example, material in the bed load may be suspended and transported with a higher velocity. The COMPETENCY of a stream is a measure of the largest particle it can transport in the suspended load. The CAPACITY is a measure of the total suspended load. In addition, streams can carry ions in solution - the CHEMICAL LOAD. Imagine constructing a dam across a river Above the dam the river begins to deposit material as it adjusts to the new base level Below the dam erosion can occur at the base of the dam. A lake forms behind the dam - becomes a temporary base level Environments of Deposition The preservation potential addresses the likelihood that deposits will be preserved in the rock record. Continental - relatively low preservaton potential: Alluvial Fans Fluvial (River) Systems Lacustrine Systems - Lakes Transitional Systems - beaches, barrier islands, washover fans, etc. Marine pelagic component (air fall plus material in the water column) turbidity currents - adds a terrestrial component to the deep sea sediment calcium carbonate compensation depth - CCCD