River Environments

• Measure mean flow velocity (v) at each subsections • Measure width (w) and depth (d) of each subsections • Calculate discharg.e Calculate the mean discharge by adding up all Qsub. Stage is easier to measure and thus often used to establish stage-discharge relationship for calculating discharge

Stream power (W)is measured in watts per unit length of stream channel,

  W = r gQS

Laminar flow: smooth stream line flow with no lateral mixing and no turbulent eddies.

Turbulent flow: a flow contains a complicated pattern of eddies with much of flow mixing. Velocity profile is logarithmic.

Part 2: Use Reynolds # to distinguish turbulent vs. laminal flow. When Re<500=laminal. When Re >2000=Turbulent

If Fr = 1, the flow critical. If Fr < 1, then U < C, the flow is subcritical. If Fr > 1, then U > C, the flow is said to be supercritical

If Fr < 1, then U < C, the flow is said to be subcritical, or tranquil/streaming. In this regime, obstacles have a damming effect on the flow.

If Fr > 1, then U > C, the flow is said to be supercritical, or rapid/shooting. In this regime, obstacles help the flow moving fast downslope

When you put your hands in a river, how can you maintain the position of the hands? The friction calculated by the above equation is purely caused by sediment grains on the channel bed and is said to grain resistance. In addition, resistance to flow can also be caused by large-scale bedforms, such as ripples, dunes, and antidunes) and is said to form resistance.

Flow resistance is hard to study because flow does not have a fixed shape. 3 Zones: • Viscous sublayer • Buffer layer • Outer layer

channel roughness involves both physical arrangement of the bed surface and flow hydraulics of the given section where the channel bed is discussed

When a sediment particle is released from rest in a fluid, it accelerates because of force of gravity, but as its velocity increases, the oppositely directed drag force exerted by the fluid grows until it equals the weight of the particle. At this time, the particle no longer accelerates but falls at its terminal velocity, called setting velocity. PART 2:Drag coefficient varies with flow. laminal- settling flow small Turbulent- settling flow big

Flotation load consists of the logs, leaves, branches and other organic debris which are generally lighter than water.

Dissolved load: the material transported in solution

Sediment load: is usually considered to be the solid inorganic material

Suspended load: is sediment moving in suspension and is supported by turbulent eddies in the fluid. Bed load: is sediment moving intermittently in contact with the channel bed. It is transported by rolling, sliding, bouncing along the bed or skimming as sheets relative to the bed. Differences: suspended load travels in upper zone of slow. Bed load moves in layer closer to the bed.

Sediment yield at a measurement point on the stream divided by

The gross erosion from above the measurement point

SY peaks at annual precipitation (P) about 300 mm.

SY decreases as P < 300 mm because there is too little runoff

SY also decreases as P > 300 mm as there is too much vegetation

A sediment budget employs conservation of mass to quantify sediment sources, sinks, and pathways in a watershed.

A reservoir is, a place where something is kept in reserve, for later use. Most often, a reservoir refers to an artificial lake, used to store water for various uses.