Exam 2 Geology

Streamflow

Stream runoff is crucial for humans as it provides

-Drinking Water

-Transportation

-Waste Disposal

-Recreation

-Commerce

-Irrigation

-Energy

Streamflow

Streams are powerful agents of change

-Flowing water erodes, transports, and deposits sediments

-Sculpts Landscapes

-Transfers mass from continents to oceans basins

Earth is the only planet in solar system with flowing water

Recharging Streams

1. Direct Precipitation or snowmelt

2. Surface runoff

3. Flow through soil

4. Infiltration

5. Groundwater Recharge

Forming Streams

Streamflow begins as moving sheetwash ( think water flowing over a parking lot)

Sheetwash erosion creates tiny rill channels.

Rills coalesce, deepen, and downcut into channels

Headward Erosion

Lengthens channels upslope. The stream valley grows towards the headwaters

What happens over time?

Over time, smaller tributaries join larger trunks stream

The array of connected channels comprise a drainage network

The specific patterns reflect the underlying geology

Dendritic

Branching, “treelike”

-Rocks of uniform strenght

-Rocks are relatively flat

Radial

Like spokes of a wheel

-conical hill or mountain

-common for volcanoes

Rectangular

right angle flow

-Rocks fracture/faulted in two main directions

Trillis

Named for gardening structure

-folded, alternating layers of hard and soft rock

Drainage Basins

(watersheds, catchments) generally, a watershed is the area of land drained by a stream or network of stream

-all of the water at same place

Drainage Divides

Watersheds can be defined for smallest of tributaries or at the continental scale

continental divides separate flow to different oceans

Watershed size & Stream

Stream size is function of stream order  (number of tributaries)

1st order = 0 tributaries

2nd order = 1 tributary

3rd order = 2 tributaries

Nth order = N–1 tributaries

High order = lots of tributaries = draining large area

Perennial

Flows all year

at or above water table

Ephemeral

flows only during and after rainfall

above water table

“How big is that stream?” Velocity and Discharge

Velocity: distance divided by time

Discharge: volume divided by time

Depth: Hydraulic pressure from overlying water column

Discharge equations

Q= volume/time

Q=area * velocity

ft x ft x ft= volume

time in seconds: ft3/sec

Q=area * velocity

Area = ft * ft=ft2

Velocity= ft/sec

ft2* ft/sec= ft3/sec

If area decreases (channel gets smaller) what would happen to velocity?

wetted perimeter= 19m, depth= 6, width= 12m

Fastest flow is in center of channel (when straight- rare in nature)

Wetted perimeter= 32m, Depth= 2m, Width= 30 m

Larger wetted perimeter

same area

slower flow

Uniformitarianism

the idea that the present is the key to the past, allowing scientists to infer that the martian feature is likely also a delta

Turbulence

shearing against banks, rocks, floor causes water to deflect

Fluvial (Stream) processes

Erosion

Transportation

Deposition

Alluvium

sediment deposited by streams