Streams: Transport to the Ocean Gary D. McMichael/Photo Researecher

The Hydrologic Cycle Describes water’s movement on the surface P = RO + ET + I Driven by solar heat ocean water evaporates wind carries moist air over land topography can force moist air to higher altitudes as air rises, it cools, water condenses to form clouds and then precipitate as rain or snow (P) rain that falls on the land can: evaporate back into the atmosphere (E) be taken up by plants, which return water to the atmosphere called transpiration (T) flow over the ground, enter streams and rivers, and ultimately be returned to the sea; called runoff (RO) infiltrates and becomes groundwater (I)

The Hydrologic Cycle

This is the “RO” of P = RO + I + ET STREAMS This is the “RO” of P = RO + I + ET

Streams Stream : body of water flowing in a channel The floor of the channel is called the bed. The sides of the are called the banks. Flood: when bodies of water overflow their banks and water covers the adjacent land called the floodplain.

A stream system network.

Drainage basin Area of land surrounded by topographic divides in which all the water is directed to a single point In Hawaii, divides are steep & basins are small!

Mississippi River Drainage Basin

Drainage Basin of the Colorado River

Some terminology VELOCITY (V) - DISTANCE PER UNIT TIME (cm/s, mph) DISCHAGRE (Q) Total amount of water that passes a given point in a stream per unit time (m3/s) = width (m)  depth (m)  average velocity (m/s) In the U.S., this is expressed as cubic feet per second (cfs): 1 m3/s = 35.9 ft3/s

River at Low Discharge

River at High Discharge

Downstream changes

Longitudinal Stream Profile of the Platt and South Platt Rivers

Flooding Water in the stream is greater than the volume of the channel. Interval between floods depends on the climate of the region and the size of the channel In Hawaii, lots of FLASH FLOODS for mountains are steep, flood plains are small & there is lots of CONCRETE!

City Built on a Floodplain Xie Jiahua/China Features/Sygma

Recurrence interval Average time between the occurrences of a given event The recurrence interval of a flood of a given size at a given place depends on: • climate of the region • width of the floodplain • size of the channel

Annual Flood Frequency Curve

More stream terms competence: measure of the largest particles a stream can transport, proportional to v2 capacity: maximum quantity of sediment carried by stream, proportional to Q and v

Job of Streams Carry away runoff to lakes and seas Erode land (degradation) Transport and deposit sedimentary debris

JOB - TO ERODE HYDRAULIC ACTION - flowing water can pick up load STREAMS CUT, DEEPEN & WIDEN VALLEYS BY: HYDRAULIC ACTION - flowing water can pick up load ABRASION & IMPACT - solid load wears down stream bed SOLUTION - dissolves channel & load

Waterfall Retreating Upriver Donald Nausbaum

Pebbles Caught in Eddies Form Potholes Carr Clifton/Minden Pictures

Stream behavior Mostly determined by velocity and shape of channel. These factors combine to allow either laminar or turbulent flow. Turbulent flow is much more erosive & picks load up. Stream velocities may vary from 0.25 to 7 m/s.

Laminar flow Smooth sheet-like flow at a low velocity Usually confined to edges and top of stream

Laminar flow

Turbulent flow Irregular swirling flow Occurs at most rates of stream flow Keeps particles in suspension

Turbulent flow

Laminar to turbulent transition Laminar flow Turbulent flow ONERA

JOB - TO TRANSPORT Dissolved load (CATIONS) Function of stream V & Q Load is the amount of material carried by a stream in all forms: Dissolved load (CATIONS) Suspended load (fine grains) Bed load (coarse material)

Sediment Transport

Saltation

Grain Size and Flow Velocity

Lower Velocities Form Ripples

Higher Velocities Form Dunes ripples dune dune

Giant ripples in the Channeled Scablands

JOB - TO DEPOSIT As V drops, stream begins to drop its load, coarsest & heaviest first Forms are streams, deltas, alluvial fans & flood plains

Two important stream types 1. Meandering Streams Gentle gradients, fine-grained alluvium Minimizes resistance to flow and dissipates energy as uniformly as possible (equilibrium) Features: point bars, oxbow lake, migrating meanders

Meandering River Over Time

Meandering River Point Bar Peter Kresan

Meandering stream, Phnom Penh, Cambodia Oxbow Lake

Incised Meanders, Utah Tom Bean

Two important stream types 2. Braided Streams Sediment supply greater than amount stream can support. At any one moment the active channels may account for only a small proportion of the area of the channel system, but essentially all is used over one season. Common in glacial, deserts, and mountain regions.

Braided River Tom Bean

Brahmaputra River: a braided river Courtesy NASA

Typical Large Marine Delta

Alluvial Fans Michael Collier

Parts of a River System

Formation of Natural Levees

BASE LEVEL Definition is: LOWEST LEVEL TO WHICH A STREAM CAN CUT Think of it as: Elevation at which a stream enters a large body of water such as a lake or ocean

Effects of Building a Dam Original Profile Graded to Regional Base Level

Effects of Building a Dam Dam Forms New Local Base Level

Effects of Building a Dam Deposition Upstream and Erosion Downstream

Formation of River Terraces When Base Level Changes

GEOMORPHIC CYCLE STAGES OF LANDSCAPE DEVELOPMENT HILLS & VALLEYS CUT INTO SIDES OF VOLCANOES STAGES ARE: YOUTH SUBMATURE MATURE OLD AGE

GEOMORPH I C CYCLE

INITIAL STAGES OF STREAM EROSION IN HAWAII Runoff is difficult to establish for rock is very porous & slope is steep. Surface has to be sealed by chemical weathering or ash before it happens. Happens during Capping Stage Streams tend to follow lava flow margins or former lava rivers. It begins at the coast & moves upwards.

Development of an experimental drainage network - headward erosion

Typical Drainage Networks

Amphitheater-Headed Valleys In Hawai‘i, erosion of the volcanoes by stream erosion and mass wasting produces these distinctive features Caused by high rainfall, steep radial drainage, and alternating layers strong and weak rocks dipping seaward

Stream Piracy or Stream Capture

planezes

Ha‘iku Valley

Giant “SOIL AVALANCH”

Formation of the Nu‘uanu Pali

neither erosion nor deposition slope, velocity, and discharge. Graded stream Stream in which neither erosion nor deposition is occurring, due to an equilibrium of slope, velocity, and discharge.

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