Antecedent Precipitation Index (API) - An index to soil moisture in a drainage.
Attenuation - The process where the flood crest is reduced as it progresses downstream.
Bankfull Stage/Elevation - An established river stage/water surface elevation at a given location along a river which is intended to represent the maximum water level that will not overflow the river banks or cause any significant damages from flooding.
Baseflow - Streamflow resulting from precipitation infiltrating the soil and eventually moving through the soil to the stream channel.
Basin - The area contributing flow past a specified point.
Crest - The highest stage or water level of a flood wave as it passes a point.
Cubic Feet per Second (CFS) - The flow rate or discharge equal to one cubic foot (of water, usually) per second.
Data Collection Platform (DCP) - An electronic device that connects to a river or rainfall gage that records data from the gage and at pre-determined times transmits that data through a satellite to a remote computer.
Discharge - The rate at which water passes a given point, expressed in a volume per time with units of L3/T.
Flash Flood - A flood which follows within a few hours (usually 6 hours) of heavy or excessive rainfall, dam or levee failure, or the sudden release of water impounded by an ice jam.
Flood - Any high flow, overflow, or inundation by water, which causes or threatens damage.
Flood Routing - Process of determining progressively the timing, shape, and amplitude of a flood wave as it moves downstream to successive points along the river.
Flood Stage - An established gage height within a given river reach above which a rise in water surface level is defined as a flood.
Gage Datum - The arbitrary datum which all stage measurements are made from.
Headwaters - Streams at the source of a river.
Hydro Graph - A graph showing the water level (stage), discharge, or other property of a river with respect to time.
Impervious - The ability to repel water or not let water enter.
Infiltration - Movement of water through the soil surface into the soil.
Lag - The time it takes a flood wave to move downstream.
Main Stem - The reach of a river/stream formed by the tributaries that flow into it.
Mean Areal Precipitation (MAP) - The average rainfall over a given area, generally expressed as an average depth over the area.
Rating Curve - A graph showing the relationship between the stage, usually plotted vertically (Y-axis) and the discharge, usually plotted horizontally (X-axis).
Reach - The distance in the direction of flow between two specific points along a river, stream, or channel.
Runoff - That part of precipitation that flows toward the streams on the surface of the ground or within the ground. Runoff is composed of base flow and surface runoff.
Second-Day Feet - The volume of water represented by a flow of one cubic foot per second for 24 hours; equal to 86,400 cubic feet. This is used extensively as a unit of runoff volume.
Staff Gage - A vertical staff graduated in appropriate units which is placed so that a portion of the gage is in the water at all times. Observers read the river stage off the staff gage.
Stage - The level of the water surface above a given datum at a given location.
Streamflow - Water flowing in the stream channel. It is often used interchangeably with discharge.
Surface Runoff - That runoff that travels overland to the stream channel. Rain that falls on the stream channel is often lumped with this quantity.
Travel Time - The time required for a flood wave to travel from one location to a subsequent location downstream.
Unit Hydro Graph - The discharge hydrograph from one inch of surface runoff distributed uniformly over the entire basin for a given time period.
Unit Hydro Graph Duration - The time over which one inch of surface runoff is distributed for unit hydrograph theory.
Wire Weight Gage - A river gage which is a weight which is lowered to the water level. The weight is attached to a cable; and as the weight is lowered, a counter indicates the length of cable released. The stage is determined from the length of cable required to reach the water level.
1 cfs-day/mi2 = 0.03719 inches of runoff
1 inch of runoff/mi2 = 26.89 cfs-day = 2,323,200 ft3 = 53.33 acre-ft
1 acre = 43,560 ft2 = 4,047 m2 = 0.4047 ha
1 mi2 = 640 acres = 2.59 km2
1 cfs-day = 24 x 60 x 60 = 86,400 ft3
Please refer to a hydrology textbook if other hydrologic equivalents are required or needed.
What volume represents 1.43 inches of runoff from a basin of 254 square miles?
Below are the daily mean flows in cubic feet per second (cfs) at a gaging station for a period of 5 days.
Day |
1 |
2 |
3 |
4 |
5 |
Flow (cfs) |
700 |
4800 |
3100 |
2020 |
1310 |
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Updated 07/17/07