OutdoorNebraska

Floating The Good Life • Nebraska Game and Parks Commission 15 While each waterway is unique, there are generalizations that apply to all rivers, including: • Over time, all rivers shift position within the landscape, some moving from side to side (laterally) while others cut down. By having room to move, adjust, and maintain channel features over time, a river system neither aggrades (builds up) nor degrades (cuts down) and remains stable. • Stability is dependent upon the river being able to transport consistently its sediment load associated with scour (sediment cut away by water forces) and deposition (sediment placed by water forces). This sediment is soil and sand particles that are washed into the river from storms as well as the river embankment material that is cut way by the force of the river flows. The sediment load then is the way rivers pick up, settle down, or move soil and sand material through its flowing system. • Rivers use meanders to dissipate energy and transport sediment. Many natural rivers have been straightened and channelized to manipulate and control flows for flood control, agricultural irrigation and recreation. These straightened channels tend to have higher flows with greater velocities. Rivers that are highly sinuous (have many meanders) are generally more stable. • The greatest energy from flowing water is exerted on the far side (exit) of the outside bend of meanders, while the least energy is exerted on the front end (entrance) of the outside bend of meanders. See Figures 3 and 4 for where these areas are located within the river. • Riverbank scouring occurs on outside banks of meanders or bends with deposition occurring on the inside banks of meanders. • Rivers have a naturally repetitive system of pools (areas of deep, slow moving water); riffles (areas of shallow, fast moving water over rocks or boulders); and runs (areas of moderately deep to somewhat shallow with moderately fast moving water and little to no turbulence). • The sequence of riffle and pool features influences the average depth of rivers, resulting in considerable variability in individual stream reaches (segments along the length of the river). • Most rivers typically exhibit different channel characteristics. They may have meanders in some reaches and be braided in other reaches. Nebraska rivers generally exhibit characteristics of one of three structural types: meandering channelized or braided. While rivers may generally exhibit one type throughout much of their system, changes in adjoining land use or direct impacts to river (construction of bridges, etc.) can result in changes from one type to another. NIOBRARA RIVER

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