Environmental Science Test 1

Sustainability (socity)

Lives within the Earth’s capacity to provide resources for future generations. Being able to maintain a system or process for an indefinite period of time. Populated in less-developed countries, more-developed countries.

The tragedy of the commons

When the self-interest of individuals destroys natural resources being shared by society.

Ecological Footprint

A measure of human demand on the Earth’s biosphere: compares human demands to nature with the ability to regenerate resources and provide service.

Role of streams in the Earth system

The basic role is due to drain water from the landscape and transport sediment.

Hydrologic flow

Most precipitation moves into the group (instead of flowing on the surface). Ground water moves more slowly than surface water.

Discharge

The volume of water flowing past a specific point into a stream over a given time period.

Baseflow

Groundwater that discharges to the surface.

Groundwater baseflow

Is important to maintaining a healthy stream ecosystem in humid climates because it provides streams with a steady flow of water during dry periods.

Discharge Basin

The land area the collects water for a given network of streams.

Surface (overland) flow and groundwater baseflow affect stream discharge…

• Heavy/prolonged rain events create heave overland flow and a spike in discharge.

• Lag as water migrates through channels, etc.

• Heavy enough discharge can be greater than stream capacity= food.

• Groundwater contributions can keep stream flowing during dry conditions.

Upper Valley

Vertical erosion with hydraulic action, abrasion and attrition dominant processes.

Traction and saltation at high flow.

Load size is large and angular.

V shaped valley.

Middle Reaches

Channel is deeper and wider.

Vertical erosion decreasing in importance, more lateral erosion and deposition.

Suspension is the main transportation type.

Land becomes smaller and less angular.

Lower Reaches

Channel is at its widest and deepest and may be tidal.

Deposition more important than erosion.

Large amount of load but the size is very small and rounded.

Sediment and streams

Movement of material by a stream is dependent on the stream’s energy and discharge (depth and velocity).

Movement can be both lateral (i.e. cut banks and sand bars) or vertical (i.e. deep channels and potholes).

Stream erosion and channel migration

As flowing water moves through a bend in a channel, water velocity increases on the outer bank.

This causes erosion and undercutting forming on overhang that eventually collapses.

Later migration over time produces wider valleys.

Deposition

Sorting leads to channel deposits called bars.

Headwaters (i.e. more energy to the system) dominated by coarse gravel and boulders.
Downstream (i.e. lower energy) dominated by the sand in crescent shaped meander bends.

Can produce relatively pure deposit of sand and clay.

Deposition - River Valleys and Floodplains

As streams cut towards base level, their gradient decreases.

These cause more mending, cutting a wider floodplain footprint.

During a flood event, the floodplain would be created with water.

Receding water leaves behind nutrient rich sediments.

Deposition- Natural Levees and Backswamps

Natural levees form along channels during overflow events.

Again, dissolved and sediment loads can be nutrient rich (and pollutant rich).

Floodplain

An area of low-lying ground adjacent to a river, formed mainly of river sediments and subject to flooding.

Deposition- Deltas

Deltas form at the mouth of rivers where the system energy has decreased.

Energy loss causes sediment deposition.

Dissolved and sediment loads can be nutrient rich (and pollutant rich).