ESSC 110: Rivers

What is a drainage divide?

A topographic high point or ridge that separates two different drainage basins

Which drainage network geometry looks like the branches of a tree and forms on uniform substrate with gentle slopes?

Dendritic

A drainage network forming on the sides of a tall volcano, flowing outward from the peak, is classified as:

Radial

Which type of drainage network forms in areas with alternating parallel ridges and valleys of hard and soft rock?

Trellis

How is a stream's discharge calculated?

Cross

Where is the water flow velocity generally the fastest in a straight river channel?

Near the water surface and towards the center of the flow

The muddy, brown color of a river after a heavy rainstorm is primarily caused by which type of sediment transport?

Suspended load

What defines the "ultimate base level" for most river systems?

Sea level

What happens to a local base level, like a resistant rock ledge causing a waterfall, over time?

The river eventually erodes it away

In a meandering river, where does the most active erosion take place?

On the outside bend of the meander

In a meandering river, where does sediment deposition occur to create a "point bar"?

On the inside bend

How is an oxbow lake formed?

A river cuts through a thin meander neck, abandoning the old meander loop

What does it actually mean if an area is in a "100

year floodplain"?

Which characteristic defines an ephemeral stream (dry wash)?

It only flows occasionally because the water table is lower than the streambed

Natural levees are built up along the banks of a river. When does this sediment get deposited?

During floods, when water spills over the banks, shallows out, and loses velocity rapidly

Which river valley shape typically forms in softer, soil

mantled hillslopes where sediment slides down into the incising stream?

Which type of river consists of multiple interweaving strands across a floodplain and actively shifts its channels on an annual basis?

Braided river

What is the primary process that causes a newly formed channel head to migrate further uphill over time?

Headward erosion

Before a distinct river channel even forms, how does rainfall initially move across the landscape?

As sheetwash, flowing in a thin layer over the surface before focusing into a depression

While the "suspended load" makes water look muddy, what makes up the "bed load" of a river?

Larger sediment, like sand and gravel, that rolls or bounces along the bottom of the stream

What is the direct relationship between a river's water flow velocity and its ability to transport sediment?

Fast

Which type of river is typically found in steep, mountainous settings and completely lacks a floodplain or natural levees?

Straight river