CIV 3102 Module 06: Discharge Measurements and Storage Reservoir Management

Practice flashcards for CIV 3102 Module 06 covering runoff estimation, streamflow measurement techniques, and the management and hydrology of storage reservoirs.

Surface Runoff

The water that flows over the ground surface, consisting of overland flow and interflow, occurring when the rain falls with an intensity ($I$) greater than the rate of infiltration ($f$).

Hortonian Overland Flow

Occurs when the rainfall intensity exceeds the infiltration capacity of the soil.

Rational Method

A method used to estimate runoff rate given by the equation $Q = \frac{C \times I \times A}{360}$ where $Q$ is the runoff rate ($m^3/s$), $C$ is the dimensionless runoff coefficient, $I$ is the rainfall intensity ($mm/hr$), and $A$ is the total area ($ha$).

Time of Concentration ($T_c$)

The time taken by a drop of water to flow from the furthest or most hydraulically distant part of the catchment to the outlet or pour point.

Kirpich Methods

Equations used to estimate the time of concentration for either overland flow in small watersheds or channel flow within the watershed, based on the longest distance of flow ($L$) and slope ($S$).

Cook's Method

A runoff estimation technique that sums numbers assigned to three factors—vegetation cover, soil type and drainage, and land slope—to calculate a catchment characteristic ($CC$).

Curve Number (CN) Method

A relationship developed by the Soil Conservation Service ($SCS$) that estimates direct runoff from storm rainfall based on soil hydrologic group and land use/cover.

Initial Abstraction ($I_a$)

The amount of water including surface storage, interception, and infiltration that occurs prior to runoff, estimated as $I_a = 0.2 \times S$ in the Curve Number method.

Unit Hydrograph

A hydrograph with a runoff depth of $1\text{ cm}$ or $1\text{ mm}$ resulting from a rainstorm of a specified duration and areal pattern.

Hydrometry

The science of water measurement, including the measurement of river stage and discharge.

Stage

The water level of rivers, lakes, and reservoirs measured using instruments like staff gauges, float-operated gauges, or depth sensors.

Price Current Meter

A device consisting of six cone-shaped cups mounted on a vertical axis that rotate in flowing water to measure local water velocity.

Mean-section Method

A discharge computation method where discharge is calculated as $Q = \frac{v_{i-1} + v_i}{2} \times \frac{d_{i-1} + d_i}{2} \times (b_i - b_{i-1})$.

Mid-section Method

A discharge computation method where discharge is calculated as $Q = v_i \times d_i \times \frac{b_{i+1} - b_{i-1}}{2}$.

Rating Curve

A graph establishing the relationship between the height of water in the river (stage) and several spot discharge measurements.

Dilution Gauging

A tracer method for discharge measurement based on the two-component mixing equation: $Q = \frac{q(C_1 - C_2)}{C_2 - C_0}$, where $C_1$ is the tracer concentration and $C_0$ is the background concentration.

Manning Equation

A formula used in the slope-area method to estimate river velocity ($V$) as a function of the hydraulic radius ($R$), downstream slope ($S$), and Manning's roughness coefficient ($n$).

Dead Storage

The volume of water stored below the outlet level of a reservoir that cannot be released by gravity, used for sediment accumulation and ecological stability.

Live (Active) Storage

The usable volume of water stored between the Full Reservoir Level ($FRL$) and the Minimum Drawdown Level ($MDDL$).

Safe Yield

The maximum dependable withdrawal that can be reliably provided from a reservoir during critical dry periods.

Mass Curve Method

A procedure used to estimate reservoir capacity by plotting cumulative inflow against time and determining the maximum vertical deficit below a demand line.

Rule Curve

A management tool that guides storage targets and release decisions, defining upper limits for maximum storage and lower limits for minimum desirable storage.

Flood Attenuation

The process by which a reservoir stores part of an incoming flood to reduce the peak discharge and downstream flooding.

Eutrophication

A water quality problem in reservoirs characterized by excess nutrients causing algal blooms, foul smell, and fish deaths.

Piezometer

An instrument used for monitoring reservoir safety by measuring water pressure or seepage within the dam structure.