Hydrograph and Flood Concepts

Hydrograph

• Falling Limb: Portion of a hydrograph showing a decrease in discharge from a peak.
• Flood Hydrograph: Graph showing the variation of hydrological data, like discharge or stage, over a time period.
• Rising Limb: Portion of a hydrograph showing an increase in discharge leading to a peak

Flood

• Flash Flood: Flood of short duration with a high peak discharge.
• Flood Control: Measures taken to protect land from overflow and minimize flood damage.
• Flood Crest: Highest point of water level during a flood.
• Flood Forecasting: Predicting flood characteristics like stage, discharge, duration, and time of occurrence.
• Flood Frequency: Number of floods exceeding a specific discharge or stage over a certain time period.
• Flood Marks: Natural marks on structures or objects indicating the maximum flood stage.
• Flood Plain: Flat land bordering a stream, only flooded when the stream exceeds its capacity.
• Flood Probability: Probability of a flood reaching or exceeding a certain stage or discharge in a year.
• Flood Protection: Measures taken to protect land from overflow and minimize flood damage.
• Flood Routing: Techniques used to calculate flood wave movement and shape changes through a river reach or reservoir.
• Flood Warning: Advance notice of potential floods.
• Flood Wave: Rise in streamflow to a maximum crest followed by recession, caused by precipitation, snowmelt, dam failure, or hydroelectric releases.
• Flooded Area: The area covered by water when streamflow exceeds channel capacity or due to downstream damming.
• Flooding: Overflow of water beyond normal stream boundaries or water accumulation in non-submerged areas.

Other Terms

• Backwater: A raised water level in a stream caused by an obstruction.
• Flow Duration Curve: A curve showing the percentage of time flow is equal to or greater than given amounts, irrespective of chronological order.
• Frequency Analysis: Analyzing past hydrological events to predict future probabilities of occurrence.
• Frequency Curve: A curve relating the possible values of a hydrological event to its occurrence frequency
• Frequency Distribution: A specification showing how the frequencies of a population are distributed according to their variable values.
• Probable Maximum Precipitation (PMP): The statistical upper limit of precipitation for a given duration in a particular basin.
• Rate of Flow: The volume of water flowing through a river cross-section in a unit of time.
• Rating Curve: A curve showing the relationship between stage and discharge in a stream.
• Recession: Period of declining discharge following a peak, shown on the falling limb of a hydrograph
• Return Flow: Flow returning to a stream or groundwater after use.
• Return Period: The average time period for an event to be equalled or exceeded.
• Risk: The potential realization of unwanted consequences of an event, a combination of probability and consequence value.
• River: A large stream acting as the drainage channel for a basin.
• River Basin: An area with a common outlet for surface runoff.
• River Bed: The lowest part of a river valley, shaped by water flow and where sediment and runoff primarily move during interflood periods.
• Runoff: The portion of precipitation that becomes streamflow.
• Runoff Coefficient: Ratio of runoff depth to precipitation depth.
• S-curve: A hydrograph resulting from an infinite series of sequential excess rainfall increments.
• Sediment Concentration: The ratio of dry solid weight to water/sediment sample weight.
• Sediment Discharge: Discharge of sediments from a stream at a specific cross-section.
• Serial Correlation: Correlation between members of a time series and those lagging or leading by a fixed interval.
• Significance: An effect is statistically significant if the hypothesis that the effect is absent is rejected.