Groundwater is what soaks into the ground and saturates it after precipitation. Groundwater generally moves very slowly and flows down to base level which can be temporary such as a lake or permanent base level which is sea level. Uplifted rock or a drop in sea level or a change in resistance can cause downcutting which can be seen in rapids and waterfalls where the edge is being worn away. Deep v shapes are a sign of heavy downcutting. Gradients can also increase causes rapids and waterfalls. Aquitards are areas that slow or prevent water movement. Aquifiers, like sand and gravel, on the other hand let ground water move freely through them. Henri Darcy discovered that the steeper the slope of the water table the faster the water will move due to increased pressure. He also found that velocity was varied by the permeability of material and the viscosity of the fluid. A well is a hole dug to reach down to where the saturated groundwater is. Artesian wells occur when the groundwater is force by pressure to rise above the aquifier. As groundwater moves it carries material that is depositied downstream as sediment but even large boulders can be moved. Streams and tributaries feed streams which can also gain or lose water to groundwater. A downgradient occurs when groundwater is flowing down, usually from gravity An upgradient is the direction water flows in an aquifier and can go higher than other areas. Streams sort sediment because it is easier to move fine particles than larger ones. Some particles are dissolved (load) in the solution, some are suspended (load) and the rest are sliding or rolling on the bottom (bed load). Capacity is the maximum amount of solid particles that can be moved by the stream per unit time. Competence is how well a stream can move material based on size rather than just quantity. Generally faster streams have greater competence. Stream valley types include Bedrock channels where bedrock is abraded alluvial channels where sediment is deposited moved and redeposited, meandering channels where much material is still suspended and tends to form sweeping bends, and braided channels where complex networks of streams are formed and can even form small islands and gravel bars. The most common drainage pattern is the dendritic pattern which forms irregular branching tributary streams similar to a trees converging branches. Radial Drainage patterns form into a pattern like spokes on a wheel and are found on volcanoes or hills. Rectangular drainage occurs when bedrock has many crisscrossing joints. Trellis drainage patterns occurre when multiple tributary streams are parallel to each other.