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 As rivers age and slow they deposit sediment and form sediment structures. How are sediments and sediment structures important to the river ecosystem? Background The focus of this lesson is the deposition and erosional effects of slow-moving water in low gradient areas. These "mature rivers" with decreasing gradient result in the settling and deposition of sediments and the formation sediment structures. The ri Duration: 60 Minutes.