CORE PHYSICAL Topic 1 medium

• Hydrology and fluvial geomorphology covers the cycle of water between the atmosphere, lithosphere, and biosphere; the drainage basin system functions as an open system allowing energy and matter movement across boundaries.

Drainage Basin System

• The hydrological cycle includes precipitation (PPT) as an input and evapotranspiration (EVT) and runoff as major outputs, with leakage as a possible third output.
• Water is stored in vegetation, surface, soil moisture, groundwater, and water channels.
• People globally modify channels and store water through various practices, including irrigation, drainage, and groundwater extraction.

Outputs: Evaporation and Evapotranspiration

• Evaporation involves liquid to gas change, while sublimation is solid to gas; evaporation, critical across oceans and seas, increases in warm, dry conditions but decreases when cold and calm.
• Temperature affects evaporation the most.
• Other factors impacting evaporation are water availability, vegetation cover, and surface color (albedo).
• Transpiration allows water vapor to escape from plants into the atmosphere; evapotranspiration (EVT) combines evaporation and transpiration, representing significant water loss.
• Evapotranspiration is most important for water loss, accounting for almost all annual precipitation loss in arid areas and 75% in humid ones.
• Potential evapotranspiration (P.EVT) is water loss with unlimited soil water for vegetation.
• The distinction between actual EVT and P.EVT relies on moisture availability.
• Actual evapotranspiration in Egypt is less than 250mm, but potential reaches 2000mm due to high temperatures.
• Cacti can reduce moisture loss.

River Discharge and Stores

• River discharge is how water moves in channels, entering as direct precipitation, surface runoff, groundwater flow (baseflow), or throughflow.
• Interception is catching and storing water by vegetation, featuring interception loss (water retained), throughfall (water falling through gaps), and stemflow (water trickling down trunks).
• Interception is less effective with grasses compared to deciduous woodland due to smaller surface areas; coniferous trees intercept more in winter, switched in summer.

Soil Water and Field Capacity

• Soil water is subsurface water in soil and layers above water table; it can be absorbed, held, or transmitted downwards/upwards.
• In coarse soils, water is in larger pores at low suctions.
• In fine soils, there are higher amounts of smaller pores holding water at high suctions.
• Field capacity is the water amount after excess water drains.
• Wilting point is moisture content where plants permanently wilt.

Soil Moisture Budget Variations

• Soil moisture deficit: soil moisture falls below field capacity.
• Soil moisture recharge: precipitation exceeds potential evapotranspiration.
• Soil moisture surplus: soil is saturated, so water flows over surface.
• Soil moisture utilization: water is drawn to surface through capillary action.

Global Water Reservoirs

• Water reservoirs by volume: Oceans (1350000.0 km³), Land (35977.8 km³). Freshwater is mainly stored in ice caps/glaciers (27500.0 km³) and groundwater (8200.0 km³).
• Channel storage is for surface and channel stored water.
• Rivers can be seasonal and disappear underground.
• Throughfall is water falling through vegetation or dropping from leaves/twigs; stemflow trickles down branches.
• Overland flow is water over the land.
• Below-ground water depends on the rock's porosity (capacity to hold water) and permeability (ability to transmit water).

Factors Influencing Infiltration

• Infiltration is how water soaks into soil; infiltration capacity is rain absorption rate.
• Infiltration decreases as rainfall continues, with rates of 0-4mm/hour on clays and 3-12mm/hour on sands.
• Vegetation increases infiltration and slows rain impact.
• Overland flow is water over the land's surface.
• Infiltration varies inversely with surface runoff; impacts depend on rainfall duration, prior saturation, porosity, plant cover, raindrop size and slope angle.

Soil Water Movement

• Percolation is slow water downward from soil to bedrock, varying by rock permeability.
• Throughflow carries water through ground in natural pipes.
• Baseflow is groundwater seeping into riverbeds and streams.
• The phreatic zone is permanently saturated, the water table is its upper layer, and the aeration zone is seasonally wet/dry.
• Aquifers are water-containing rocks, like sandstone and limestone, acting as natural water regulators. Springs form where water flow reaches surface.
• Groundwater recharge occurs by infiltration, seepage, leakage, and artificial recharge; losses result from evapotranspiration, natural/artificial discharge, and leakage.

Activities to Minimize Groundwater Loss

• Minimizing groundwater loss includes evapotranspiration, natural discharge, groundwater leakage and outflow, and artificial extraction.
• Artificial extraction has caused drastic water table declines in areas like the High Plains of Texas and Saudi Arabia.

Hydrographs

• A storm hydrograph tracks river discharge changes in a short time, showing groundwater-fed baseflow, quickflow from storm runoff, a rising limb, and a recessional limb after peak flow.
• Rising limb: increase in water
• Recessional Limb: decrease in water in river
• Peak flow: maximum river discharge and time lag is delay between storm peak and maximum flow.

River Regimes

• River regime: annual discharge variation. It's Influenced by precipitation, rocks/soil, basin shape, plant/soil cover.
• Climate is the main factor.
• The Shannon exhibits expected temperature regime, Gloma/Kemi surge in spring thaw, while Po shows rainfall/snowmelt peaks.

Factors Influencing Hydrographs and River Regimes

• Simple regime: river has one peak; complex regime: multiple peaks, is shown for the River Rhine, as it has many tributaries going to a variety of environments.
• Urban growth raises peak flow, shortens time lag from increasing impermeable ground and the channel drainage.
• The influences include climate, rainfall intensity/type, temperature/evaporation/transpiration, and prior moisture.
• Smaller, circular basins respond fast; high drainage and impermeability also quicken response.
• Vegetation and soils reduce surface runoff and boost delays; permeable surfaces absorb, and steep slopes increase runoff.

Erosion

• Abrasion (corrasion) erodes bed and bank by mechanical impact of debris.
• Attrition wears down load, creating rounder pieces.
• Hydraulic action uses air/water force, with turbulence-driven cavitation.
• Corrosion/solution dissolves chemical ions, especially calcium, at rates depending on the rock, concentration, and water flow.

Factors Affecting Erosion

• Load, velocity, gradient, geology, pH, and human interference affect the erosion rate.
• Global sediment output converts from yearly sediment/solute loads to fluvial denudation.
• Output shows land surface rates, displaying regional fluctuation from 10 to 10000 tonnes/km² annually due to varying rates of erosion.
• Global Suspended Sediment reflects contributing elements like weather conditions and geography.
• Load transport consists of the movement of small particles (silts and clays) in transit as suspended load. Load occurs when larger particles travel via saltation or bed/tracted load, and when it occurs material is moved in solution.

Deposition and Flow Patterns

• Causes of deposition: shallowing slope, water decrease, friction increase.
• Types of flow: Laminar (smooth, rare), Turbulent (high velocity, rough channel), and Helical (spiraling).
• Velocity and discharge affect stream power. There's critical river erosion velocity based on soil type (Hjulstrom Curve), and velocity/energy based on channel bed pitch, water flow, channel type, and friction.