Southwest Florida Feasibility Study Hydrologic Performance Measures

Mike Duever (19 May 2002)

1. Duration of Uninterrupted Inundation.

The mean duration of all inundation events during the xx-year period of record is the performance measure. This performance measure will be automated so that an inundation event is defined as the number of weeks from when water >0.0 ft until water < 0.0 ft, but it is not considered an inundation event unless water comes above 0.0 ft for 4 weeks or longer. The target would be to have the duration of uninterrupted inundation be within 10 percent (plus or minus) of NSM conditions. Other than NSM targets can be specified for individual indicator regions as appropriate.

2. Number of Dry Events.

Dry events are defined as times when the water level drops either to or below the ground surface. Two dry events that are separated by a flood event when the water level rises to less than 0.0 feet above the ground surface for less than 4 weeks are grouped as one dry event. In that case, the duration of the dry event is calculated as the sum of the two dry events and the intermittent flood event. This performance measure is the number of dry events during the xx-year period of record. The target would be to have the number of dry events be within 10 percent (plus or minus) of NSM conditions. Other than NSM targets can be specified for individual indicator regions as appropriate.

3. Hydroperiods.

Hydroperiods are defined as the average number of days per year when the water level is at or above the ground surface during the xx-year period of record. The target would be to have the hydroperiod be within 10 percent (plus or minus) of NSM conditions. Other than NSM targets can be specified for individual indicator regions as appropriate.

4. Duration of Water Level Deviation.

Three levels of deviation will be defined as follows: (1) the number of weeks when the NSM water table is below ground and is 1, 2, or 4 ft higher or lower than the proposed condition, divided by the number of weeks the NSM water table is below ground; (2) the number of weeks when the NSM water table is above ground and is 0.25, 0.50, and 1.00 ft higher or lower than the proposed condition, divided by the number of weeks the NSM water table is above ground. The target would be to have the duration of water level deviation for the lowest level of deviation be no more than 10 percent of the number of weeks in the period of record used in the model. Other than NSM targets can be specified for individual indicator regions as appropriate.

5. Seasonal Amplitude and Interannual Variability of Water Levels.

This performance measure uses weekly average water depths above and below ground to compare the seasonal fluctuation and year-to-year variation in water levels with NSM values. The target would be to have the seasonal amplitude and interannual variability be within 10 percent (plus or minus) of NSM conditions. Other than NSM targets can be specified for individual indicator regions as appropriate.

6. Water Levels and Timing.

Evaluate water levels relative to the ground surface and timing in each Indicator Region in southwest Florida. Format for the model output is monthly, wet season, dry season, and annual average water levels. The target would be to have the water levels be within 10 percent (plus or minus) of NSM conditions for each of the four time intervals. Other than NSM targets can be specified for individual indicator regions as appropriate.

7. Water Flows to Tide.

Evaluate amounts of water going to tide as point discharges in channels, as sheet flow across a transect, or as groundwater seepage through a vertical plane. Format for the model output is monthly, wet season, dry season, and annual average water flows. The target would be to have the total flows in any designated area be within 10 percent (plus or minus) of NSM conditions for each of the four time intervals. Other than NSM targets can be specified for individual areas as appropriate.

Performance measures 1-6 could be estimated for all of the southwest Florida indicator regions, or a representative selection of them, in terms of spatial distribution and habitat type.