HYDROMET FINALS

Runoff

-          Movement of precipitation across the land surface

Catchment

-          Land area which rain falls

Watershed

-          Land area that contributes surface runoff to any point of interest. Land area where all surface water drains into a common water body

Drainage Basin

-          Tract of land drained by a river and its tributaries

Surface Runoff

-          Rain falling on a watershed in quantities exceeding the soil or vegetation uptake

Divides

-          Lines separating the land surface into watersheds

Surface water

-          Any body of water found on the Earth’s surface

Weather Hydrology

-          Movement of water along the earth’s surface as a result of precipitation. Important for transportation, irrigation, water supply, hydropower, etc.

Surface Water Hydrology

-          Movement of water along the earth’s surface as a result of precipitation. This includes runoff and overland flow. Important for transportation, irrigation, water supply, hydropower, etc.

Surface Runoff

-          Draining or flowing off of precipitation from a catchment area through a surface channel enters into a stream channel. Represents the output form catchment in a given unit of time.

Overland flow

-          A thin sheet of water that flows over the land surface. Reaches first the stream channel

Interflow

-          Part of the precipitation that infilters, moves laterally through upper crusts of the soil and returns to the surface at some locations away from the point of entry into the soil. Also known as through flow, storm seepage, subsurface flow, or quick return flow

Ground water flow

-          When water percolates into the ground as deep seepage and builds up the ground water table (GWT)

Hortonian Overland Flow

-          Hypothesized that overland flow occurred when the rainfall rate was higher than the infiltration rate of a soil

Direct runoff

-          Part of runoff which enters the stream immediately after the rainfall. It includes surface runoff, prompt interflow and rainfall on the surface of the stream. Delay time is less

Base flow

-          Delayed flow that reaches a stream essentially as groundwater flow.

Runoff and Overland Flow

-          Its affecting factors are climate factors, catchment characteristics, human activities, and hydrological factors

Climate Factors

-          These are precipitation, temperature, and wind

Catchment Characteristics

-          These are topography, soil type, and vegetation

Human Activities

-          These are urbanization, agriculture, and deforestation

Hydrological Factors

-          These are antecedent moisture condition, and drainage networks

Streamflow

-          Also known as runoff water, at a particular outlet in a river is the total collection of water coming from its watershed or drainage basin. Composed of the overland flow or surface runoff, channel, interflow, and groundwater flow

Streamflow or Discharge, m3/sec, ha-m/day

-          volume of water that moves over a designated point over a fixed period of time

Streamflow measurements

-          show information on changes in discharge valuable for predicting flooding, estimating long-term trends in water and sediment discharges, and for distinguishing possible long-term climate change

Velocity and flow of river

-          affects food sources and migration of fish amongst other wildlife

Velocity-Area Method (Float Method)

-          Rough approximation of flow in a uniform and straight channel. Velocity of the float gives the surface or maximum velocity of water in the channel, and should be multiplied by about 0.85 to approximate the average velocity.

Pygmy meter

-          A wheel is rotated by water flow and the rate of the rotation signifies the water velocity. It is primarily used in measuring discharge

Vortex meter

-          Velocity is proportional to the downstream frequency of the vortex flow and is read on a digital readout. It used for measuring flow in pipes

Current meter

-          Electronic pulses determine water velocity. Can be used in large bodies of water like oceans to measure the current. Based on many field tests, for flow depths less than 0.5m, the average velocity of the stream vertical is at six-tenths depth below the surface. For depths of 0.5m or greater, the average of the velocities at two-tenths and eight-tenths depth below the surface, equals the mean velocity in the vertical

Q = 3.33 (L – 0.2H)H^3/2

-          Value of Q for a rectangular weir in terms of feet

Q = 1.84 (L – 0.2H)H^2/3

-          Value of Q for a rectangular weir in terms of meter

Q = 2.5 H^5/2

-          Value of Q for a 90° V-notch weir in terms of feet

Q = 1.379 H^5/2

-          Value of Q for a 90° V-notch weir in terms of meter

Slope-Area Method

-          Determining the discharge using Manning’s Flow equations

Hydrograph

-          of a river outlet is a graph of stage or discharge versus time.

Streamflow hydrograph

-          obtained from a recorder of water level or discharge installed at the gaging station of the river. A result of the runoff processes compromising overland flow, interflow, and base flow that are generated by precipitation storms

Base Flow

-          contributions from the delayed interflow and groundwater runoff

Direct runoff

-          contributions from surface runoff and quick interflow.

Unit hydrograph

-          analysis refers only to direct runoff.

Rising Limb

-          portion of the hydrograph, composed mostly of surface runoff

Crest

-          zone of the hydrograph around peak discharge

Recession or falling limb

-          zone of the hydrograph after the peak discharge. Duration to fall from peak to base flow

Time to peak (t_p)

-          duration from the start of direct runoff to peak flow.

Time of base (t_b)

-          duration that runoff is above the base flow

Time concentration (t_c)

-          duration of water from farthest point in the watershed to reach outlet

Time lag (t_t)

-          of the basin is the time between the center of mass of the runoff-producing rainfall to the peak rate of flow (q_p)

Groundwater

-          supplies more than 50% of the potable water supply and 85% of the piped water supply in the Philippines. In arid regions, it is often the only reliable source of water for irrigation

Aquifer

-          Water bearing geologic formation capable of transmitting water through its pores at a rate sufficient for economic extraction by wells

Aquitard

-          Rather impervious nature, which transmits water at a slow rate compared to an aquifer

Aquiclude

-          Can absorb water but cannot transmit significant amounts

Aquifuge

-          No interconnected pores; neither absorb nor transmit water

Porosity (n)

-          is a measure of the water-bearing capacity of the formation

Specific yield (S_y)

-          refers to the volume of water, expressed as a percentage of the total volume of the saturated aquifer, that will drain by gravity when the water table (Ground Water Table (GWT) drops due to pumping or drainage. Depends upon grain size, shape, and distribution of pores and compaction of the formation. The values of these for alluvial aquifers are in the range of 10-20% and for uniform sands about 30%

Specific retention (S_r)

-          percentage volume of water, which will not drain by gravity

Confined aquifer

-          known as artesian aquifer; where a porous formation underneath is sandwiched between two impervious strata (aquicludes) and is recharged by a natural source at a higher elevation so that the water is under pressure in the aquifer. T = Kb and is independent of the piezometric surface.

Piezometric surface

-          level where water rises from artesian aquifer in the well to its initial level at the recharge source.

Unconfined aquifer

-          known as the water table aquifer; where there is homogeneous porous formation extending from the ground surface up to an impervious bed underneath and rainwater percolating down in the soil saturates the formation and builds up the GWT. T = KH, where H is the saturated thickness. As the water table drops, H decreases, and the transmissibility is reduced.

Water table well

-          a well drilled into the unconfined aquifer

Storage coefficient

-          volume of water given out by a unit prism of aquifer (i.e., a column of aquifer standing on a unit horizontal area) when the piezometric surface (confined aquifers) or the water table (unconfined aquifers) drops by unit depth. Refers to the volume of water given out by a unit prism of aquifer when the piezometric surface (confined aquifers) or the water table (unconfined aquifers) drops by unit depth

Darcy’s law

-          states that ‘the velocity of flow in a porous medium is proportional to the hydraulic gradient

Transmissibility

-          is the flow capacity of an aquifer per unit width under unit hydraulic gradient and is equal to the product of permeability times the saturated thickness of the aquifer.

Wells

-          Form the most important mode of groundwater extraction from an aquifer.

Cone of depression

-          It is when the water table assumes a conical shape due to the radial flow into the well through the aquifer

Drawdown

-          drop in the water table elevation at any point from its previous static level.

Area of influence and its extent radius of influence

-          area extent of the cone of depression

Unsteady flow

-          the phase at constant rate of pumping where the drawdown curve develops gradually with time due to the withdrawal of water from storage as the water table elevation at a given location near the well changes with time

Steady flow conditions

-          the drawdown surface attains a constant position with respect to time when the well is known to operate under this condition

Recuperation or recovery

-          it is a stage and an unsteady phenomenon when the pumping is stopped and then the depleted storage in the cone of depression is made good by groundwater inflow into the zone influence. Then there is a gradual accumulation of storage until the original (static) level is reached

Ground water

-          is widely distributed under the ground and is a replenishable resource unlike other resources of the earth

Specific capacity

-          is the discharge per unit drawdown in the well