Central Florida, encompassing the area between Daytona and Tampa, contains numerous lakes—and many sink holes, which occur due to the weakening and collapse of the supporting layer of limestone beneath the ground surface. In fact, it is understood that a majority of the lakes in this area (“sink hole alley”) were formed as sink holes appeared and filled with ground water from the large underlying aquifers.
In April of 1986, a sinkhole appeared at the edge of a small lake known as Grace Lake, located next to Interstate 4 about 20 miles north of Orlando. The initial depression and opening was around 10 ft. in diameter, and it was able to reduce the 14 acre lake to a small pond in a matter of days. As described here, it would then take 31 years for the sink hole to naturally plug itself, but, in the interim, lake residents would spend countless hours trying to find ways to restore the lake, and learned much about urban planning and the importance of community involvement in the process.
Early view of Grace Lake Sink Hole. Photo Credit: Mark Kamrath
In the beginning, in the immediate aftermath of the sinkhole’s appearance, residents did everything from using a shovel and dumping yard debris to fill the sinkhole (then, 10 feet in diameter) to contacting the local home owners’ associations and the county government. Residents held meetings and tried to come up with a solution, but no one could come up with a structured approach to filling the sinkhole and restoring the lake.
For a couple of years, the lake did fill and there was hope that the sink hole had repaired itself. However, in 1988, the sinkhole reopened and grew in size, causing the lake to again disappear. This time, and for nearly three decades, only the heavy annual rains associated with the rainy season (June through October) would cause the lake to partially fill, only to drain again as the level of the Floridan aquifer went through its annual cycle.
During this period, there was stepped-up levels of grass-roots activity aimed at getting the attention of the local government (Seminole County) authorities to address the situation. Not only were the residents disturbed by the loss of their lovely lakeside environment, and property values, but there was, fortunately, much more to it on a larger scale.
Since Grace Lake is part of the Seminole County storm water drainage system, and receives considerable runoff from the Interstate, the continuous drainage of the lake directly into the aquifer, a primary source of drinking water, was felt to be a serious concern. This environmental and public health issue was to become the main driving force behind the effort to restore the lake. (Note: In Florida, drainage of ground water into the aquifer is not that uncommon, and is part of the aquifer recharging process, but allowing a large sink hole to act as a “drainage well” in a drainage basin next to a busy interstate highway, as was the case here, was believed to be a violation of the relevant water management regulations.)
In 2001, local residents contacted the Seminole County Department of Public Works and the St Johns River Water Management District to learn more about the lake’s health and to inquire about a way to restore it. Contact was also made with the Department of Environmental Protection and the Florida Department of Transportation. During this process, residents met with engineers, hydrologists, and other experts and came to the conclusion that more study of the lake was needed.
In 2004, after much discussion, about 30 residents of the North Ridge and North Cove subdivisions, which are located around the lake, raised enough money to commission a geotechnical study that would assess the lake’s hydrology and propose an engineering solution to remediate the sinkhole and restore the lake. That study was conducted by Devo Engineering of Orlando. It concluded that the repair of the sink hole was technically and economically feasible, and recommended a rather straightforward method to plug it.
Armed with their engineering study, residents returned to both Seminole County and the St. Johns River Water Management District asking for them to act. For one reason or another, the county engineers did not feel that it was their responsibility. The Water Management District told us that the first step in the process of implementing the engineers’ recommendations, whoever was going to do it, was to file an application for an “Environment Resource Permit”. So, as instructed, the necessary paperwork was obtained, and the application process was started, making use of the talents of a recently retired engineer in the local group. However, it was not long before it became clear that the type of data and analysis, including computer modeling of the local drainage basin, as was required to complete the application, would be out of reach for the small group of local residents involved.
It also became evident that, one way or the other, the local group would have to find a way to effectively apply pressure on the county officials so that they would accept the sink hole, and the drainage of raw untreated runoff from the lake into the aquifer, as their responsibility. It was then that one of the home owners, who was well-connected to local political circles, was able to get the attention of key county officials. This, in turn, cleared the way for a contingent of residents to appear before the Board of County Commissioners to present their case, and, at the end, obtain some indication that the county would take over the permitting process, and take on the job of repairing the sink hole and restoring the lake.
After some delay, and regular “reminding” by local residents, the county hired their own engineering consultants to conduct the necessary modeling and come up with a design for the repair. Initially, the county’s approach was much more complicated and expensive than originally recommended by the residents’ engineer. It provided for concrete structure with an overflow gate that was intended to maintain a maximum lake level to avoid downstream flooding. But, after further analysis and several design iterations, the county engineers finally adopted the original relatively simple and cheaper approach to plugging the sinkhole, and finally budgeted the funds to implement the fix.
Overall, this process took approximately 10 years to complete, due to numerous delays, an economic recession, budget cuts, and other factors, including, it is believed, reluctance on the part of the county storm water engineers to lose a substantial amount of storm water storage volume, which the sink hole had provided by causing the lake to empty in the first place. It turns out that such reticence to giving up that much valuable storage volume was well founded.
During the period of 2013-2015, the county legal department put an additional hurdle in the way of progress by requiring signed easements from each home owner located on the one side of the lake where there didn’t already exist a county “drainage easement”. Unfortunately, the process of obtaining these easements became totally bogged down, and, even with a door-to-door campaign to convince reluctant home owners to sign, again caused a long delay in the project.
However, an unexpected change in project management at the county level resulted in a rethinking on this legal requirement, and the need for the easements was finally rescinded in the fall of 2015.
At the same time, in October-December, 2015, as Grace Lake was expected to recede (as it had been doing regularly for some 27 years prior), so that the work could commence, it was surprisingly observed that the level of the lake hardly went down at all. In fact, as some unusual heavy fall rains fell, Grace Lake even reached its historical outfall level, where it overflows though a conduit under the Interstate roadway. This conduit leads to a portion of the lake that was cut off from the main body of the lake when the interstate was built in the 1960s. This, in turn, caused flooding of a local church school’s soccer field, which happened to be installed in this cut-off part of Grace Lake. As might be expected, a consequence of this was that much blame was placed on the county for “fixing the sink hole and causing the flooding”. Of course, this happened in spite of the fact that the work to repair the sink hole never started.
At this point, the county, with the help of lake residents, began to monitor lake levels closely, and, since the lake water level hardly fell in spite of the return of the dry season, it was determined at the start of the summer, 2016, that the sinkhole had naturally plugged itself, and the project was removed from the list of active county capital improvement projects.
At the end of the summer of 2016, and near the official end of the hurricane season in Florida, Hurricane Matthew arrived dumping 9 inches of rainfall over night, and, with Grace Lake being nearly full at the time, it again caused threats of downstream flooding. Once again, complaints arose that the county was at fault for not preparing adequately for such an event. The loss of storm water storage volume that Grace Lake once provided caused all downstream retention ponds to reach unprecedented levels, and near flooding conditions.
Then, during the summer of 2017, continuous heavy summer rains caused Grace Lake to reach its outflow level by the end of July. So, the lake offered no help to the storm water drainage system when, on September 10, Hurricane Irma arrived with its record levels of rainfall. Grace Lake water levels peaked at more than 4 ft. above its outflow level, flooding many yards around the lake and causing flooding to downstream retention ponds, yards and streets. In one downstream neighborhood, residents had to drive through a foot or more of water flowing across the road to get to their homes. And once again, the county was called upon to help, and pumps were use to move water from one pond to the next in an attempt to alleviate the flooding.
All of this because the Grace Lake sink hole had repaired itself, and removed many acre-feet of storage for the storm water.
Not only that, but the return of Grace Lake has led to a new set of problems for residents and various agencies to grapple with, especially in regard to the appearance of hydrilla and other noxious aquatic weeds that would eventually choke the lake if left untreated. Debate among residents occurred in regard to the best way to treat Grace Lake following various environmental guidelines. The most heated debates concerned the degree to which the recommended herbicides should be used safely, combined with the introduction of a limited population of sterile “grass carp” to control the weeds. Eventually, enough resident support was obtained to form an MSBU (Municipal Services Benefit Unit) to pay for the Seminole County Lake Management Program to treat the lake, but only after much effort to educate residents about its benefits and the County Commissioners voted to approve the MSBU.
So, 30-plus years after the appearance of the Grace Lake sink hole, and the beginning of a decades-long saga of ground-roots involvement with local government agencies to repair it, Grace Lake is currently near full, under treatment for aquatic weeds, and is part of the Florida Lake Watch program at the University of Florida.
Sunset over Grace Lake. Photo Credit: Harry Jaeger
About the Authors: Harry Jaeger and Mark Kamrath