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Droughts in Ohio: Shall We be Worried?
Tiao J. Chang
Department of Civil Engineering
Russ College of Engineering, Ohio University
Athens, Ohio 45701
Prepared for the WMAO 2009 Fall Conference
November 5, 2009
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Precipitations in OhioGeographic Distribution (World Book)
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Precipitations in OhioTemporal Distribution (ODNR)
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Streamflows in Ohio:Athens Gauging Station (USGS)
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Streamflows in Ohio:Delaware Gauging Station (USGS)
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Ohio - Blessed Land
As far as
water is concerned,
it is promised.
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Streamflows in Ohio:Athens Gauging Station (USGS)
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1988 Drought in the Midwest
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1988 Drought in the Midwest (Athens Messenger, 6-10-1988)
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1988 Drought in the Midwest (Athens Messenger, 6-9-1988)
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1988 Drought in the Midwest (Athens Messenger, 6-20-1988)
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1988 Drought in the Midwest (Athens Messenger, June 1988)
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How to Define Droughts(AWRA Journal, October 1990)
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A 100-year Drought?(AWRA Journal, October 1990)
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Truncation Level of Drought IndicatorsStreamflow, Precipitation, Reservoir Level
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Drought DefinitionTemperature and Groundwater Drawdown
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Levels of Drought Severity
• 70% Drought Severity
• 80% Drought Severity
• 90% Drought Severity
•95% Drought Severity
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A Drought Monitoring Method
• Operable under existing conditions– Palmer Drought Severity Index (Palmer, 1965)
• Technically effective
• Acceptable by all parties
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Drought Indicators
• Streamflow
• Precipitation
• Groundwater Level - drawdown
•Temperature -
•Reservoir Level -
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Scioto River Basin
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Streamflow
Gauging
Stations (18)
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Example of Truncation Levels: Daily Streamflow
• Olentangy River at Delaware
• Mean daily flow: 10.00 cms
• 70% Truncation Level: 0.911 cms
• 80% Truncation Level: 0.651 cms
• 90% Truncation Level: 0.453 cms
• 95% Truncation Level: 0.312 cms
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Precipitation
Gauging
Stations (21)
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Temperature
Gauging
Stations (13)
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Groundwater
Wells (14)
&
Reservoirs (4)
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Precipitation
Gauging
Stations (21)
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Mean Drought Durations
•
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Conditional Probabilityfrom 70% to 80%
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Severity Levels of Streamflow Drought
•Based on daily flow monitoring, a drought event is between two levels of severity
– Duration of current event ≥ Mean drought duration– Conditional probability ≥ 0.50
• Levels of Severity Selection– Gauging Stations– Indicator: majority of gauging stations
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Gauging Stations in the Basin
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Basinwide Drought Severity Levels
• Streamflow drought plus at least one other indicator exceeding the severity level of streamflow drought - Level of streamflow drought is selected.
• Streamflow drought plus at least one other indicator reaching 70% but not exceeding that of streamflow drought – 70% is selected
• Streamflow not reaching 70% but at least two other indicators are – 70% is selected
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Test for April 1988
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Test for May 1988
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Test for June 1988
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Summary: The monitoring method
• Groundwater drawdown indicated the drought event at the earliest stage.
• Precipitation is the most sensitive drought indicator.
• Based on the definition as stated, streamflow becomes the most critical basinwide drought indicator?
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Flood vs. Drought
• Reservoirs operated for flood control only
• Can that be for drought management?
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Four Reservoirs in the Basin
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Requirements for the Optimization Model
• Minimum release is required for each reservoir.
• Minimum streamflow at control stations according to demands at a given drought severity level.
• Mass conservation of a reservoir.
• Minimum reservoir elevation for a reservoir.
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Assumptions for the Optimization Model
•Maximum Release - the amount enclosed between the specified reservoir elevation and the 70% truncation level of the reservoir.
• Area Factor- contribution of a reservoir to a downstream control station is proportional to the drainage area of a reservoir.• Distance Factor - contribution of a reservoir to a
downstream control station is inversely proportional to the distance of the reservoir from the control station.
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Expression of Area Factor
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Expression of Distance Factor
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Objective Function of the Optimization Model
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Constraints for Minimum Flows at Control Stations
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Constraints for Mass Conservation of Involved Reservoirs
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Constraints for Minimum Releases from Involved Reservoirs
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Example of Constraints for 70% Drought Severity
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Example for Deer Creek- April 1988
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Example for Deer Creek-May 1988
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Example for Deer Creek-June 1988
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Example for Paint Creek-May 1988
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Example for Paint Creek-June 1988
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Example for Paint Creek-July1988
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Example Paint Creek-August 1988
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Paint Creek - September 1988
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Summary:The Optimization Method
•
• Daily monitoring of drought severity as defined enables an optimum model for management using flood-control reservoirs.
• The developed area factor and distance factor rationalize conflicting constraints for
competing uses under the stress of water shortage.
• The safe yield of a reservoir estimated based on drought severity levels eases the operation of the reservoir.
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Water in Ohio Yin: Shortage of water; Yang: Too much of water
Yin and yang are complementary
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Personal Reflections
• ConservationMass, Energy, and Momentum
• Equilibrium Water and Watershed