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River Me<:henlca end Geomorphology e it ever exactly lhe same as any olher time or place. It is constantly adjusting to an ever changing hydrograph and sediment load, which are constantly adjusting to the weather patterns a ld land uses." 2.2.1 Channel Regime - Regime i! a term that is bantered about frequently wilh regard to fluvial study and has taken on ;everal meanings. It is generally regarded (and will be so in this manual) to mean the geometric condition of a river reach which is in a stale of quasi-equilibrium. Such a rellCh is said to be "in regime", or "graded". And allhough it may experience temporal ;md spatial variation in form and discharge of sediment or water, lhe variations fluctuate llbout a balanced mean. For most mobile-bed streams a range of discharges exist wilhin which lhe stream can adjust itsdf by variation of bed fonns, flow deplh, and velocity, wilhout appreciably changing its slope. channel widlh, or average bed elevation. Floods and lhe actions of man are the primary impetus to changes in channel regime (Chang 1988). 2.2.2 Channel Planfonn - Natural channels occur in three general fonns: straight, braided. and meandering. Many investigators have developed classification systems to further define a river's fonn. A classification of river types by Brice (1983) based on four major planfonn properties lhat are flOOily observed for this manual. The properties include: sinuosity, point bars, braiding, and anabranchin8. Four major river types. each wilh commonly occurring planfonn properties. are illustrated by increasing slope in Figure 2-1. Sinuous canalifoITl rivers, as exemplified by lhe Arickaree River have a flat slope, characterized by narrow crescent-shaped point bars. a notably unifonn width. a lack of braiding. and a moderate to high sinuosity. The channel is relatively narrow and deep, is laterally stabile and has a high silt-clay content for the banks (Chang 1988). Sinuous Ioint-bar rivers (see examples in Figure 2-1) are steeper and have more rapid rates of lateral migration at bends, although straight reaches may remain stable for long periods of time. Such rivers tend to have greater width at bend apexes; they also tend to have prominent point bars that are visible at nonnal stage (Chang 1988). Sinuous hraided rivers, as shown by Figure 2-1. are steeper and wider than sinuous point-bar rivers with the same discharge, have rapid IateS of lateral migration and rapid shifts in the position of the thalweg. Such rivers have fairly heavy bed-material load but less silt-clay content. Point bars are more irregular as the braiding increases (Chang 1988). Nonsinuous braided rivers without point bars exist on steep slopes with heavy bed material load and low silt-clay content. An example is given in Figure 2-1. Such rivers are highl)' braided and have moderate rates of lateral migration at random places where one of the multiple branches impinges against a bank. The branch channels shift at random within the banklines (Chang 1988). e 4 Colorado Erosion Control Manual