AIH Professional Hydrologist - Groundwater Examination flashcards
AIH Professional Hydrologist - Groundwater Examination · Build recall with a focused review session.
31 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Hydrologic water balance
- The conservation equation P = ET + Q + ΔS + G, stating that precipitation is partitioned into evapotranspiration, runoff, storage change, and groundwater outflow over a defined period.
- Field capacity
- The water content a soil retains after excess water has drained by gravity, typically reached two to three days after saturation. It sets the upper limit of plant-available water.
- Wilting point
- The soil moisture content at which plants can no longer extract water and wilt permanently. It is the lower limit of available water capacity.
- Available water capacity
- The difference between field capacity and wilting point, representing the volume of water a soil can store and release to plants.
- Horton infiltration equation
- An exponential decay model in which infiltration capacity starts high and declines toward a constant rate as the soil surface wets and seals during a storm.
- Manning's equation
- An empirical formula for open-channel velocity, v = (1/n) R^(2/3) S^(1/2), relating velocity to roughness, hydraulic radius, and channel slope.
- Rational method
- A peak discharge formula, Q = CiA, using a runoff coefficient, rainfall intensity, and drainage area to estimate peak flow for small catchments.
- Unit hydrograph
- The direct runoff hydrograph produced by one unit of effective rainfall over a specified duration, used to scale runoff responses to other storm depths.
- Time of concentration
- The travel time for water to flow from the hydraulically most distant point of a catchment to its outlet; it governs the critical storm duration for peak discharge.
- Flow-duration curve
- A cumulative frequency plot of discharge versus percent of time exceeded, used to characterize the variability and low-flow behavior of a stream.
- Baseflow separation
- A hydrograph technique that divides total streamflow into direct storm runoff and delayed groundwater discharge, often using an exponential recession curve.
- Rating curve
- A site-specific relation between stage and discharge, typically a power function, used to convert continuous water-level records into discharge estimates.
- SCS curve number
- A method estimating direct runoff depth from rainfall using a curve number that reflects soil group, land use, and antecedent moisture conditions.
- Return period
- The average interval between events equaling or exceeding a given magnitude, equal to the reciprocal of the annual exceedance probability.
- Muskingum routing
- A flood routing method using storage S = K[xI + (1-x)O], where K is a travel-time constant and x controls hydrograph attenuation.
- Double-mass analysis
- A plot of cumulative catch at one gauge against a reference gauge, used to detect a change in record consistency such as a gauge relocation.
- Water year
- A twelve-month period, October 1 through September 30 in U.S. practice, chosen so that a full snow accumulation and melt season falls within one year.
- Rational method assumptions
- The method assumes uniform rainfall intensity over the catchment for a duration equal to the time of concentration, with a constant runoff coefficient.
- Hydrograph recession limb
- The declining portion of a hydrograph after peak flow, reflecting drainage of catchment storage; its slope is used to estimate baseflow recession constants.
- Darcy's law
- The governing equation of groundwater flow, Q = -KA(dh/dL), stating that discharge is proportional to hydraulic conductivity, area, and hydraulic gradient.
- Hydraulic conductivity
- A property of a porous medium and fluid describing the ease of water movement under a hydraulic gradient; it has units of length per time.
- Specific yield
- The volume of water an unconfined aquifer releases from storage per unit area per unit decline in water table, equal to drainable porosity.
- Storativity
- The volume of water released from aquifer storage per unit surface area per unit decline in hydraulic head, dimensionless.
- Transmissivity
- The product of hydraulic conductivity and saturated aquifer thickness, expressing the rate of water transmission through a full aquifer thickness per unit width.
- Theis equation
- A transient solution for drawdown around a pumped well in a confined aquifer, using the exponential integral well function and aquifer storativity and transmissivity.
- Cooper-Jacob approximation
- A straight-line simplification of the Theis solution valid at small u values, plotting drawdown versus log time to obtain transmissivity and storativity.
- Thiem equation
- A steady-state radial flow solution relating pumping rate, transmissivity, and drawdown between two observation points at known radii from a well.
- Potentiometric surface
- An imaginary surface representing the hydraulic head in a confined aquifer; groundwater flows perpendicular to its contours, from high to low head.
- Ghyben-Herzberg relation
- A principle stating that the freshwater lens extends below sea level about forty times the height of the water table above sea level in coastal aquifers.
- Flow net
- A graphical construction of orthogonal equipotential lines and flow lines used to estimate seepage quantity and pore pressures through a porous medium.
- Pumping test analysis
- Interpretation of drawdown versus time data from a controlled well test to estimate aquifer transmissivity, storativity, and boundary effects.