Hydrology 2

Vocabulary flashcards covering key hydrology terms related to infiltration, groundwater, and runoff based on lecture notes.

Porosity (n)

Ratio of void volume to total soil volume; indicates total storage capacity of a soil.

Effective Porosity

Portion of total porosity that can drain or fill with water (n – θ_i).

Saturation Zone

Near-surface soil layer where moisture content is 100 % during infiltration.

Transmission Zone

Layer below saturation zone where water moves downward but is not fully saturated.

Wetting Zone

Intermediate layer with increasing moisture content between wetting front and saturated soil.

Wetting Front

Sharp boundary separating newly saturated soil above from drier soil below during infiltration.

Infiltration Rate (f)

Rate at which water enters the soil surface; units of cm h⁻¹ or in h⁻¹.

Potential Infiltration Rate

Infiltration rate when water is ponded on the surface; actual rate ≤ potential rate.

Cumulative Infiltration (F)

Total depth of water infiltrated over time; F(t)=∫f dt.

Green-Ampt Method

Physically based infiltration model with a sharp wetting front; yields F–t relationship.

Wetting Front Suction Head (ψ or y)

Average capillary suction at the wetting front used in Green-Ampt calculations.

Darcy’s Law

q = –K Δh/Δz; describes laminar flow of water through porous media.

Hydraulic Conductivity (K)

Soil property indicating ease of water flow; units of length per time.

Ponding Time (t_p)

Elapsed time from rainfall onset to surface ponding; t_p = (ψK Δθ)/(i(i–K)).

Horton Infiltration Equation

Empirical formula f = fe + (f0 – f_e)e^(–kt) describing exponential decay of infiltration capacity.

Sorptivity (S)

Soil parameter representing capillary suction effect; appears in Philip’s infiltration solution.

Baseflow

Portion of streamflow supplied by groundwater seepage between storms.

Surface Runoff

Water that travels over land to a channel after rainfall exceeds abstractions.

Rational Method

Q_p = C i A; estimates peak runoff from small catchments assuming uniform rainfall.

Runoff Coefficient (C)

Dimensionless factor expressing fraction of rainfall that becomes runoff in the Rational Method.

Streamflow (Discharge)

Volume of water passing a stream cross-section per unit time, commonly expressed as cfs.

Stilling Well

Device that converts water-surface elevation to discharge at a gauging station.

Weir

Small overflow structure with a calibrated notch used to measure discharge via head-depth.

Current Meter

Instrument that measures point velocity in flowing water for discharge computation.

Hydrograph

Plot of stream discharge versus time at a specific location.

Annual Hydrograph

Discharge record covering an entire year, showing seasonal variation.

Storm Hydrograph

Discharge response of a watershed to a single rainfall event.

Baseflow Separation

Technique to partition a hydrograph into baseflow and direct-runoff components.

Phi-Index (φ)

Constant abstraction rate yielding excess rainfall depth equal to direct runoff depth.

Direct Runoff

Runoff generated from excess rainfall that reaches the channel quickly.

Effective (Excess) Rainfall

Portion of rainfall not lost to abstractions; produces direct runoff.

Unsaturated Zone (Vadose Zone)

Soil region above the water table where pore spaces contain both air and water.

Capillarity

Upward or lateral movement of water in soil due to surface tension and pore size.

Water Table

Upper surface of the saturated zone where pore pressure equals atmospheric pressure.

Confined Aquifer

Water-bearing layer bounded by impermeable strata; water under pressure.

Unconfined Aquifer

Water-bearing formation with a free water table open to atmospheric pressure.

Artesian Well

Well tapping a confined aquifer where pressurized water rises above the aquifer top; may flow freely.

Cone of Depression

Lowering of the water table around a pumping well.

Contamination Plume

Zone of polluted groundwater extending downgradient from a source.

Advection (Groundwater)

Transport of contaminants with bulk groundwater flow.

Dispersion

Spreading of a contaminant plume due to velocity variations and molecular diffusion.

Retardation

Delayed contaminant movement caused by sorption onto soil particles; velocitywater / velocitycontaminant.

Chemical Precipitation (Groundwater)

Process where dissolved contaminants form solids and cease moving with groundwater.

Biotransformation

Microbial degradation or transformation of contaminants within the aquifer.