What combination of factors both natural and man-made is necessary for healthy river restoration, and how does this enhance the sustainability of natural and human communities? Objective Seasonal weather patterns affect the flow patterns of water into the rivers (and watersheds) of western North America. What landform features can form when erosion is caused by fast–moving water from Spring and Fall rains, and snowpack melt runoff? Background The focus of this lesson is to learn about the seasonal flow patterns of rivers in Western North America, and the erosional effects of fast-moving water. Duration: 60 Minutes.