In 1922, Florida began construction on what is now called the Melbourne-Tillman Water Control District (MTWCD). They constructed levees to protect the area from flooding by the Upper St. Johns River (USJR), and a canal network was excavated to improve drainage. The C-1 canal, the main canal for this drainage network, directed the runoff from the MTWCD into Turkey Creek toward the Indian River Lagoon (IRL).
This historic project created an interbasin diversion of approximately 100 square miles that reduced freshwater runoff west into the USJR basin and increased the undesirable freshwater flow east into the IRL via Turkey Creek. The reduced freshwater flow from the USJR reduced the water supply available for downstream users. The increased storm-related freshwater discharge periodically depressed salinity below desirable levels for prolonged periods, producing increased stress on the IRL estuary ecosystem. The associated pollution attenuated light penetration into the water column and limited the coverage and density of sea grass habitat.
In 1972 the Florida legislature passed several key natural resource bills, one of which created regional water management districts. These districts became stewards of the environment, and were able to begin addressing impacts such as this historic freshwater diversion.
In 2010, the St. Johns River Water Management District (SJRWMD) of northeast Florida sponsored drainage modifications for the MTWCD in efforts to reduce the runoff from their fresh water drainage system into the IRL. However, a major modification to their historic operations and gate system, known as MS-1, was necessary. The modifications included altering the method by which the MTWCD had historically discharged this fresh water. In exchange for the MTWCD adopting these revised discharge protocols, the SJRWMD replaced the aged gate system. The objective of the new discharge protocols is to divert some water that used to go east into Turkey Creek and send it west to be pumped toward the USJR.
The historic MS-1 structure housed a navigation lock, along with four flood control gates. Two of the gates at MS-1 were radial gates and two were AMIL gates. Those four gates and decommissioned lock were replaced with six overshot gates. All six new gates are fully automated, and controlled by a bank of four Campbell Scientific CR1000 dataloggers. Using LoggerNet software, the dataloggers are programmed to measure twin water-level sensors upstream and a single sensor downstream of the gates. The software is installed on computers in the MTWCD and SJRWMD office, and is also installed on a SJRWMD laptop computer, giving managers the flexibility to control the gates from any location. Two cameras are positioned to view the gates, and they interface with the dataloggers and software to enable remote viewing of the site.
The Campbell Scientific equipment runs in automatic mode for most flow and flood control situations, with minimal need for staff intervention. All operations of the gates are monitored by the equipment: every water level, all six gate positions, rainfall, and others. In addition to this, the Loggernet program continuously calculates the discharges flowing over the gates, and reports these values to the operators. Two basic operational regimes have been programmed into the controlling dataloggers: gate control and flow control. With gate control, an operator can set any of the six gates at any elevation, where they will stay until moved again. In flow control, the operator will specify any flow value, say 575 cubic feet per second (cfs). Because the Loggernet system constantly calculates the gate flows, this operational regime allows the dataloggers to physically move the gates based upon the desired flows. As water levels rise or fall upstream of the gates, the flows calculated will become higher or lower than the desired example of 575 cfs. Once Loggernet detects that the flow it calculates has moved out of the range, or tolerance, of between 570 and 580 cfs, the system will adjust the gates until these flows are again within that tolerance. This mode will constantly monitor and move the gates as needed until an operator modifies the operational regime. The option to override and go into manual operation is available whenever managers need it.
With these flow controls, the system limits discharges from the C-1 canal into Turkey Creek, no matter what the upstream water levels are. Emergency conditions are accounted for and the system is programmed to handle tropical storm and hurricane conditions when initiated by an operator. In these modes the gates are incrementally opened through any countdown desired (typically 72 hours) to allow more flow through as a tropical storm or hurricane advances to the area. After the storm threat has passed, or at any point in the countdown, the system can be switched back to automatic flood-control mode.
The main advantages of all the gate and operational modifications include the ability to raise the level of the upstream canal to divert water as needed, and the discharging waters that pass over the gates are more advantageous upper-level water that has a higher oxygen content than the lower-level water the other styles of gates discharged (for better water quality in Turkey Creek). These overshot gates also reduce sediment transport and turbidity in the discharge water. All these improvements obtain the ultimate goal of reducing fresh water discharge into the IRL estuary, resulting in the reduction of nutrients and other pollution into the Indian River Lagoon.