By Paul N. Gray, Ph.D., Manager
Updated on 5-17-01, adapted from an oral presentation.
The REAL problem with water levels in Lake Okeechobee, even with WSE in operation, is we do not have enough places in South Florida to store water. Until storage is fixed, no schedule for the Lake will meet all our goals.
Overhead______________________________________________________________
the average annual inflow: 7.5 feet
the average annual evaporation 5 feet
the average annual outflow 2.5 feet
Over the past 31 years, the average uses of the outflow have been
agriculture 1.5 foot
urban and LEC water supply 0-6 inches
estuaries/other ~1 foot
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*Assume the Lake area is 470,000 acres. Inflow data set from Trimble, Santee, and
Neidrauer 1997. “Including the effects
of solar activity for more efficient water management: an application of neural networks.” proceedings of the Second International
workshop on artificial intelligence applications in solar-terrestrial physics)
(over a 66 year period).
*Outflow data for agriculture and urban uses are estimated from the “Lake O Regulation Schedule Study” Appendix B, page B-5 “Total EAA/LOSA Irrigation Demands and Demands Not Met for the 1965-1995 simulation period.”
*Evaporation figure from William Walker’s DRAFT model of Lake O phosphorus dynamics—LOTAC committee
Narration: so, 7.5 feet flow in, 5 evaporate back out, and we have to get rid of 2.5 feet—in an average year.
One and a half feet goes to agriculture, 0-6 inches to LEC, and there is about one foot that has to go to the estuaries (these are very rough estimates and depend on how much rain falls, where it falls, and when). That one foot is the water we can work with. If we run water down the St. Lucie at 1600 cfs, which is the supposed threshhold between a safe release and a harmful one, and run water down the Caloosahatchee at 2,800 cfs, which is the safe threshhold for that estuary, then it takes about 54 days to get rid of this one foot of water. In practice, these estuaries also drain water between the Lake and the outlet—so we could not do “54 days of full releases,” but rather would release more gradually.
Therefore, with “operational flexibility” we can manage in the manner described above and get rid of this water without problems by arranging these “54 days worth of flow” in an appropriate matter.
Conclusion: In a “normal year” we can manage the lake fine:
But Florida is a land of extremes.
the average annual inflow: >10 feet
the average annual evaporation 5 feet
this year’s outflow >5 feet
Over the past 31 years, the average uses of the outflow have been
agriculture 1.5 foot
urban and LEC water supply 0-6 inches
estuaries/other 3.5 foot (or more)
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In one-fifth of the years (from Trimble’s 66year data set), the Lake received more than 10 feet of inflow. If we assume the same evaporation/ag/urban/LEC use, we need to get 3.5 feet of water down the estuaries, instead of the one foot in normal years. If it takes 54 days to get rid of 1 foot of water, it will take 188 days to get rid of 3.5 feet. In these years, so much other water would be flowing through these canals we can not find 188 “open” days to release this water and estuary harm occurs. (for example, in the Indian River Lagoon area—their estuary flows now are about 140% of natural—because of drainage—so in wet years, they harm their estuary before any Okeechobee water is released, i.e., there are not any days to release Okeechobee water, let alone 188 days).
SO, in at least one in five years, we get damage to the Lake, or estuaries, or both—no matter how much operational flexibility we use. We just don’t have anywhere else to put that water.
We can see this same effect in predictions from the CORP’s “Water Supply and Environment” (WSE) Lake level management plan.
overhead______________________________________________________________
-the Caloosahatchee River will have damaging releases (>2800 cfs) 27 times
-the St. Lucie River will have 31 damaging releases (>1600 cfs)
-Lake Okeechobee will have prolonged deep water events 4 times
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(The data for this table taken from “Lake O Regulation Schedule Study” presentation to SFWMD Governing Board April 15, 1998)
This is NOT the fault of WSE, any operation schedule would have similar problems because we just don’t have anywhere to put extra water during wet events.
What about DRY years?
the average annual inflow: 3.4 feet
the average annual evaporation 5 feet
this year’s outflow none (deficit)
Over the past 31 years, the average uses of the outflow have been
agriculture 1.5 foot
urban and LEC water supply 0-6 inches
estuaries/other minus 3.2 feet (or more)
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We get major shortfalls in water, and without system-wide storage, there is no way to accommodate all water interests.
And this is what the Comprehensive Everglades Restoration Plan (CERP) is about.
Overhead___________________________________________________________
Surface Reservoirs (>200,000 acres proposed of deep water storage)
ASR (>300 wells with 5 million gallons per day capacity)
enhance storage on private property
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The CERP proposes 3 ways to get more storage. (not only does CERP try to get more storage—but we are trying to redirect most of the Lake Okeechobee water back toward the Everglades instead of the estuaries)
Surface reservoirs: Compared with the other 2 options, reservoirs are quick, predictable, and certain. CERP calls for more than 200,000 acres. We have Talisman bought (50,000 acres in the EAA) and the Berry Groves (several thousand acres along the Caloosahatchee River). Talisman could hold 6 inches of Lake Okeechobee water. We need to do these reservoirs ASAP.
ASR: CERP plans to build about 300 of these and they have an unknown effectiveness—and unknown potential problems. Let’s fully fund the pilot projects to find out as soon as possible whether we can rely on these for storage (if not we need to make other plans).
Basin-wide storage: We still are LOSING wetlands. South Florida has a lot of storage potential that we are not fully utilizing. We need to increase wetland protection, increase storage through landowner incentives (easements, nutrient control). Indeed, CERP notes that the Everglades have lost 3 very important ecosystem attributes that must be restored: spatial extent of wetlands, habitat heterogeneity, and connectedness of habitats. If we build reservoirs, STAs, and ASR wells north of Lake Okeechobee, the 3,500 square mile Okeechobee drainage basin will get NONE of the 3 important attributes restored. RESTORING WETLANDS THOUGHOUT THE OKEECHOBEE BASIN IS THE MISSING INGREDIENT IN CERP. We need more wetland restoration.
In conclusion:
--we cannot solve water management problems with Lake O, or the estuaries, or water supply, until we get more storage.
--Reservoirs are reliable and controllable and should be built as quickly as possible.
--ASR experiments should be expedited
--wetland protection and increase in acreage needed (*key missing ingredient)