Rivers, Estuaries, and Deltas

Hydrologic Cycle

the movement and interchange of water between the sea, air, and land

Steps in the Hydrologic Cycle

Evaporation

Precipitation

Transpiration

Runoff

Infiltration

Running Water

most important geologic agent in eroding, transporting, and depositing sediment

Stream

a body of running water, confined to a channel, that runs downhill under the influence of gravity

Parts of a Stream

Headwaters

Mouth

Channel

Banks

Bed

Floodplain

flat valley floor composed of sediment deposited by the stream

Drainage Basin

the total area drained by a stream and its tributaries

Tributary

a small stream flowing into a larger one

Divide

ridge or high ground that divides one drainage basin from another

Continental Divide

separates the streams that flow into the Pacific from those that flow into the Atlantic and Gulf of Mexico

Drainage Pattern

the arrangement, in map view, of a stream and its tributaries

Types of Drainage Patterns

Dendritic

Radial

Rectangular

Trellis

Stream Erosion is controlled by 

flow velocity and discharge

Stream Velocity is controlled by

stream gradient (slope)

channel shape

channel roughness

Stream gradient

downhill slope of the streambed

Channel shape and roughness

both effect stream velocity due to drag

Stream Discharge

volume of water flowing past a given point in a unit of time

Stream Erosion occurs by three mechanisms:

hydraulic action

solution

abrasion

Categories of Sediment load

Bed load

Suspended load

Dissolved load

Bed Load

large or heavy particles that travel on the streambed

• divided into traction load and saltation load

Suspended Load

sediment that is small/light enough to remain above the stream bottom by turbulent flow for an indefinite period of time

Dissolved Load

dissolved ions produced by chemical weathering of soluble minerals upstream

Sediment Deposition

sediment temporarily deposited along stream as bars and floodplain deposits and at/near its end as deltas or alluvial fans

Bars

ridges of sediment (usually sand or gravel) deposited in the middle or along the sides of a stream

• can create braided streams if sediment is deposited in middle

Meandering Streams

flow faster along the outside of bends and more slowly along the inside, depositing point bars on the insides of the meanders

Meander Cutoffs (Oxbow Lakes)

form when a new, shorter channel is cut through the narrow neck of a meander

Delta

body of sediment deposited at the mouth of a river when flow velocity decreases

Alluvial Fan

large, fan- or cone-shaped pile of sediment that forms where stream velocity decreases as it emerges from a narrow mountain canyon onto a flat plain

Types of Deltas

wave-dominated

tide-dominated

stream-dominated

Methods of Flood Control

Dams

Artificial levees

Wise land-use planning

Downcutting

process of deepening a valley by erosion of the streambed

• typically form v-shaped valleys

Streams cannot erode below their

base level

Graded Streams

characteristic concave-up longitudinal profile

Lateral Erosion

widens stream valleys by undercutting of stream banks and valley walls as a stream swings from side to side across the valley floor

Headward Erosion

the slow uphill growth of a valley above its original source by gullying, mass wasting, and sheet erosion

Stream Terraces

step-like landforms found above a stream and its floodplain

• occurs when river rapidly cuts downward into its own floodplain

Stream Terraces can be caused by

rapid uplift

drops in base level

climate changes

Incised Meanders

retain sinuous pattern as they cut vertically downward

Estuary

semi-enclosed coastal environment where freshwater and ocean water meet and mix

Types of Estuaries

Coastal Plain

Fjord

Bar-built

Tectonic

Coastal-Plain Estuary (drowned river valley)

V shape in cross-section

• result of fluvial erosion

Fjord (drowned glacial valley)

U shape in cross-section, deep

• result of glacial erosion

Bar-built Estuary (lagoon)

sand spit or barrier island encloses embayment

shallow

Tectonic Estuary

down-dropped basin (due to plater tectonics)

located near ocean and seawater floods basin

Why are estuaries particularly susceptible to hypoxia?

Highly productive

Stratified

Most are heterotrophic