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

Precipitations in OhioGeographic Distribution (World Book)

Precipitations in OhioTemporal Distribution (ODNR)

Streamflows in Ohio:Athens Gauging Station (USGS)

Streamflows in Ohio:Delaware Gauging Station (USGS)

Ohio - Blessed Land

As far as

water is concerned,

it is promised.

Streamflows in Ohio:Athens Gauging Station (USGS)

1988 Drought in the Midwest

1988 Drought in the Midwest (Athens Messenger, 6-10-1988)

1988 Drought in the Midwest (Athens Messenger, 6-9-1988)

1988 Drought in the Midwest (Athens Messenger, 6-20-1988)

1988 Drought in the Midwest (Athens Messenger, June 1988)

How to Define Droughts(AWRA Journal, October 1990)

A 100-year Drought?(AWRA Journal, October 1990)

Truncation Level of Drought IndicatorsStreamflow, Precipitation, Reservoir Level

Drought DefinitionTemperature and Groundwater Drawdown

Levels of Drought Severity

• 70% Drought Severity

• 80% Drought Severity

• 90% Drought Severity

•95% Drought Severity

A Drought Monitoring Method

• Operable under existing conditions– Palmer Drought Severity Index (Palmer, 1965)

• Technically effective

• Acceptable by all parties

Drought Indicators

• Streamflow

• Precipitation

• Groundwater Level - drawdown

•Temperature -

•Reservoir Level -

Scioto River Basin

Streamflow

Gauging

Stations (18)

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

Precipitation

Gauging

Stations (21)

Temperature

Gauging

Stations (13)

Groundwater

Wells (14)

&

Reservoirs (4)

Precipitation

Gauging

Stations (21)

Mean Drought Durations

•

Conditional Probabilityfrom 70% to 80%

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

Gauging Stations in the Basin

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

Test for April 1988

Test for May 1988

Test for June 1988

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?

Flood vs. Drought

• Reservoirs operated for flood control only

• Can that be for drought management?

Four Reservoirs in the Basin

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.

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.

Expression of Area Factor

Expression of Distance Factor

Objective Function of the Optimization Model

Constraints for Minimum Flows at Control Stations

Constraints for Mass Conservation of Involved Reservoirs

Constraints for Minimum Releases from Involved Reservoirs

Example of Constraints for 70% Drought Severity

Example for Deer Creek- April 1988

Example for Deer Creek-May 1988

Example for Deer Creek-June 1988

Example for Paint Creek-May 1988

Example for Paint Creek-June 1988

Example for Paint Creek-July1988

Example Paint Creek-August 1988

Paint Creek - September 1988

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.

Water in Ohio Yin: Shortage of water; Yang: Too much of water

Yin and yang are complementary

Personal Reflections

• ConservationMass, Energy, and Momentum

• Equilibrium Water and Watershed