Surface Water Hydrology

Comprehensive vocabulary flashcards covering key definitions, principles, formulas, processes, and morphologic features of surface water hydrology, river hydraulics, lake limnology, and streamflow measurement.

Surface Water Hydrology

The study of moving water found in rivers, open channels, lakes, reservoirs, and surface runoff.

Stream

A body of water that flows downslope along a defined natural passageway or channel.

River

A flowing body of water characterized by a larger volume of water and a well-defined channel compared to smaller streams.

Stream Classification Hierarchy

The relative size ranking of flowing surface water bodies ordered as: $\text{River} > \text{Creek} > \text{Brook} > \text{Rill}$.

Drainage Basin (Watershed)

The fundamental hydrologic unit of land area that drains and contributes surface water to a stream system or river channel.

Drainage Divide

Topographic high points, such as ridges or hills, that define the geographic boundary separating adjacent drainage basins.

Tepuis

Table-like mountains (mesas) located within the Guiana Shield highlands of South America.

Watershed Outlet

The lowest point of elevation on a topographic map of a drainage basin, used as the starting reference when delineating a watershed boundary.

Aspect

The compass direction of exposure or orientation of sloping lands within a watershed.

Orientation (Watershed)

The general direction of the main reach of a river as it traverses downslope across a watershed.

Overland Flow

Surface runoff water moving across the ground surface toward a river or stream channel during and immediately following a storm event.

Interflow

Precipitation that infiltrates and percolates just beneath the land surface, moving laterally through shallow soil layers at a slower rate than surface runoff.

Critical Distance to Erosion ($X_c$)

The distance downslope from a drainage divide to the point where the shearing force of overland flow ($F$) exceeds the resistance of the surface material ($R$), marking where erosion begins.

Suspended Load

Fine sediment particles, such as clay and silt, that remain suspended throughout the flowing water column due to upward fluid turbulence.

Dissolved Load

Mineral ions carried in solution in stream water, produced by chemical weathering of bedrock and soils.

Bed Load

Coarse sediment particles, including sand, pebbles, and boulders, that roll, slide, or hop along the bottom of a riverbed.

Saltation

The transport of larger sediment grains bouncing, leaping, or hopping downstream along the bed of a channel.

Sediment Yield

The total mass or volume of sediment transported out of a watershed by a river over a given interval of time.

Competence

The maximum grain size or largest particle diameter that a river is capable of transporting under given flow conditions.

Capacity

The maximum total load of sediment that a river can transport at any given time.

Discharge ($Q$)

The volume of water passing through a specific cross-section of a conduit or channel per unit time, calculated as $Q = \text{Area} \times \text{Velocity}$.

Current Meter

An instrument equipped with revolving cups, impellers, or electromagnetic sensors used to measure the velocity of moving water in a stream or canal.

Six-Tenths Depth Method

A stream-gauging technique where the mean velocity is measured at $0.6$ of total depth ($60\%$ depth below the water surface) for shallow streams with a depth $\le 2.5\,\text{ft}$.

Two-Point Method ($0.2$ and $0.8$ Depth)

A streamflow gauging method used in deep sections (depth $\ge 2.5\,\text{ft}$) where average velocity is taken as the arithmetic mean of velocity readings measured at $20\%$ and $80\%$ of total water depth below the surface.

Rating Curve

A calibrated empirical plot relating stream stage (gauge height) to stream discharge ($Q$) at a gauging station, allowing continuous estimation of flow from water-level measurements.

Hydrograph

A graphical representation of stream stage elevation or water discharge plotted as a function of time.

Lag Time (Hydrograph)

The elapsed time between the center of mass or peak of rainfall and the resulting peak discharge of a river.

Baseflow

The sustained, low-flow component of stream discharge fed by groundwater seepage into the channel between precipitation events.

Headwaters (Source)

The upstream origin and uppermost streams, springs, or seepage areas from which a river system begins.

Tributary

A smaller feeder stream or river that flows into and joins a larger mainstem river channel.

Confluence

The geographic intersection point where a tributary merges into the main river channel.

Thalweg

The continuous line connecting the deepest points along the channel bed of a river.

Bank Storage

The temporary absorption and storage of water in the permeable alluvial banks of a river when stream stage rises above the local water table.

Hyporheic Zone

The subsurface region beneath and immediately adjacent to a streambed where shallow groundwater and surface river water actively mix.

Stream Order

A numerical ranking system for stream networks where headwater channels are 1st order; the confluence of two 1st-order streams creates a 2nd-order stream, and two 2nd-order streams form a 3rd-order stream.

Braided Stream

A river channel pattern characterized by multiple intertwined, anastomosing threads separated by temporary sediment bars, common in regions with steep gradients, erodible banks, and high sediment loads.

Meandering Stream

A single-channel stream that forms continuous sweeping curves and loops across a low-gradient floodplain.

Cutbank

A steep, eroded riverbank located on the outer curve of a meander bend where water velocity and erosive energy are highest.

Point Bar

A low, crescent-shaped deposit of sand and gravel accumulated on the inside bend of a river meander where flow velocity decreases.

Oxbow Lake

A U-shaped or crescent lake formed on an abandoned channel loop after a meandering river cuts across a narrow meander neck.

Natural Levee

An elevated ridge of coarse sediment deposited naturally along riverbanks during overbank flood stages as water loses transport velocity.

Yazoo Stream

A tributary that runs parallel to the main river along its floodplain for a long distance because natural levees prevent it from entering directly.

Laminar Flow

Fluid motion in which water particles travel along parallel, smoothly layered streamlines without cross-current mixing.

Turbulent Flow

A complex, swirling fluid motion featuring irregular eddies and transverse mixing, typical of most open stream channels.

Ephemeral Stream

A stream that flows only temporarily in direct response to precipitation events (e.g., wadis and arroyos) and lies entirely above the water table.

Intermittent Stream

A stream that flows seasonally when supplied by groundwater or snowmelt, but dries up completely during arid parts of the year.

Perennial Stream

A stream that flows year-round because its bed intersects the water table continuously, maintaining baseflow throughout the seasons.

Influent (Losing) River

A river whose channel sits above the regional water table, losing water by downward percolation into the underlying groundwater system.

Effluent (Gaining) River

A river whose channel lies below the local water table, receiving groundwater recharge through baseflow seepage along its bed and banks.

Stream Gradient

The downstream slope of a river channel expressed as vertical elevation loss divided by horizontal distance ($\text{Gradient} = \frac{\Delta h}{\Delta l}$), commonly in $\text{ft/mi}$ or $\text{m/km}$.

Weir

A small dam structure with a calibrated notch opening (such as a $90^\circ$ V-notch or rectangle) built across a stream channel to determine discharge from the height ($H$) of overflow.

Cirque Lake (Tarn)

A glacial lake occupying an amphitheater-like bedrock basin carved high on a mountain wall by glacial quarrying and dammed behind a terminal moraine.

Pluvial Lake

A landlocked lake formed in arid or semiarid regions during periods of historically high precipitation and lower evaporation associated with glacial epochs.

Oligotrophic Lake

A young, clear, nutrient-deficient lake with low organic productivity and minimal organic sediment on its bottom.

Mesotrophic Lake

A middle-aged lake characterized by moderate nutrient availability and organic content capable of supporting diverse aquatic populations.

Eutrophic Lake

An aging, shallow lake enriched with excessive plant nutrients and organic material that depletes dissolved oxygen levels.

Littoral Zone

The shallow shoreline area of a lake where adequate sunlight reaches the bottom to support rooted emergent, floating, and submerged aquatic vegetation.

Limnetic Zone

The well-lit, open-water surface layer of a lake located away from the shoreline.

Profundal Zone

The deep, lightless bottom zone of a lake below the euphotic depth where rooted aquatic plants cannot grow.

Epilimnion

The warm, less dense, circulating upper layer of water in a thermally stratified lake during the warm season.

Hypolimnion

The dense, cold, undisturbed bottom layer of water in a thermally stratified lake situated beneath the thermocline.

Thermocline (Metalimnion)

The intermediate layer in a stratified lake characterized by a rapid and steep decrease in water temperature with increasing depth.

Lake Turnover

The convective mixing of a lake that occurs in spring and autumn when surface waters cool to $4\,^\circ\text{C}$, become dense, and sink to displace bottom waters, homogenizing nutrients and dissolved oxygen.

Seiche

A periodic oscillation or standing wave in the water level of a lake or enclosed bay triggered by persistent winds or abrupt barometric pressure changes.

Hjulstrom Curve

A logarithmic graph illustrating the critical flow velocities required to erode, transport, or deposit sediment particles of varying grain diameters.

Sorting

The hydraulic process by which flowing water segregates and deposits sediment grains based on differences in particle size, density, and settling velocity.

Alluvial Fan

A cone- or fan-shaped deposit of river-borne sediment built where a steep, confined mountain stream debouches onto a broad, low-gradient plain.

Delta

A depositional landform formed at the mouth of a river where it enters a quiet standing body of water, such as an ocean, sea, or lake.

Rational Formula

An empirical equation ($Q = C \times I \times A$) used to estimate peak surface runoff discharge ($Q$ in $\text{cfs}$) from runoff coefficient ($C$), rainfall intensity ($I$ in $\text{in/hr}$), and watershed area ($A$ in $\text{acres}$).

Staff Gage

A graduated metal scale or ruler permanently installed in a stream, reservoir, or lake to permit direct visual reading of stage height.

Stilling Well

A vertical chamber connected to a stream via submerged intake pipes that dampens channel wave action and turbulence to enable accurate stage recording.

Stage-Capacity Curve

A graph plotting the relationship between the water-surface elevation (stage) of a lake or reservoir and its total accumulated storage volume.

Flood Recurrence Interval ($T$)

The average time interval in years between flood events that equal or exceed a specified discharge magnitude, related to annual probability by $P = \frac{1}{T}$.

Probable Maximum Precipitation (PMP)

The theoretically greatest depth of precipitation physically possible over a specific geographic area for a given storm duration.

Moisture Maximization

A numerical technique that applies the highest plausible atmospheric moisture content for a region to recorded rainfall from a historical storm to estimate maximum potential storm depths.

Nilometer

An ancient stone graduated column or well installed along the Nile River used to record annual flood stages for calculating agricultural land taxes and regulating canal gates.