Hydrologic Cycle and Fluvial Processes

Amount of Freshwater

2.5%, 1.2% is surface freshwater, and 21% is easily available in rivers/lakes surfaces

precipitation

Water (rain, snow, sleet, or hail) that falls from the atmosphere to the Earth's surface.

evaporation

Process where water from surfaces (like oceans, lakes, and soil) turns into water vapor and rises into the atmosphere.

transpiration

process where plants release water vapor into the atmosphere through small openings in their leaves

water vapor transport

Movement of water vapor through the atmosphere, usually by wind and weather patterns.

percolation

Water moving downward through soil and rocks, recharging underground water supplies.

surface flow/runoff

Water that flows over the ground (like rivers and streams) after rain or melting snow.

groundwater flow

Movement of water through underground layers of soil and rock.

residence time

at steady state, = reservoir amount/flux

global average annual precipitation

varies widely based on latitude and geography → highest precipitation is near equator, high rainfall is over tropical regions of Earth’s ocean

global average evaporation

varies widely based on latitude and geography → highest evaporation happens in high warm, sunny subtropics

watershed

drainage basin, all the land drained by river/river system. bounded by mountains/high elevation points. can be nested/contained by another wastershed.

V shape

higher elevations, river valleys have this shape as the steep gradient (slope) causes the river to flow quickly and cut down into the rock

U shape

lower elevations, river valleys have this shape as the river moves towards flatter land, so the gradient (slope) becomes gentle causing the river to slow down, eroding the sides of valley more than the bottom

stream channels

passageways where water normally run in valleys

meandering stream

river or stream that winds and curves through a valley in a snake-like pattern → fastest flow and most erosion on the outside banks, slowest flow and deposition on the inside banks

braided stream

stream that occupy many channels instead of one → common for highly variable flow and high sediment load, associated with glacier drainage

floodplains

flat surface next to the river that gets flooded occasionally, tend to have rich soil, levees (natural or manmade) are boundaries of flood plain

river sediment load

total load = quantity of sediment carried in a river = bed load (on bottom, ~10% total) + suspended load (~90%) + dissolved load (<1%, weathering products and ions)

per mil

‰, parts in 1000 parts. EX: 1 gram per 1000 grams = 1‰

salinity of oceans

represented by 35‰ as there are 35 grams of dissolved ions in 1000 grams (1 L) of ocean water, 3.5% salt.

River discharge

volume of water that flows through a river channel over a period of time, is calculated by size and speed of riverflow. Q = WDV, where W = width, D = depth, V = velocity

Hjulstrom Curve

shows the relationship between a river's flow velocity and the size of sediment (particles) it can pick up (erode), transport, and deposit.

competency

largest particle in river

dynamic equilibrium

steady state between sediment transported by a stream and sediment delivered to stream, more load → more deposition → steeper slope → higher velocity → difficult to carry load

Upstream floods

floods that are relatively local, shorter duration due to precipitation

Downstream floods

wider area, longer duration due to saturated soils.

magnitude/frequency concept

floods follow this concept where smaller floods occur more frequently, while larger, more extreme floods are rare but have severe consequences.

Effects of urbanization

reduced infiltration with more impervious surfaces (like roads, sidewalks, and buildings), increased runoff with more flows into streams as less water absorbed, flashy discharge where there is increased flow → more erosion and greater flood risks downstream

Channelization

adjustment to flood hazards by modifying a river’s flow through straightening, deepening, lining channels with concrete. can reduce flooding but increase flow velocity (risking downstream floods + erosion)

restoration

adjustment to flood hazards by reestablishing natural flow patterns, vegetation, and wetlands. slows water, increase infiltration, reduce flood impacts