Three sites were selected for this project (Fig. 7-1). These sites were selected to provide a range in water retention characteristics (Table 7-1). One site (Chiquita) was selected because of the presence of impoundments that were designed to retain water. These impoundments were constructed on a site that was primarily uplands. The second site (CPI) was selected because it did not hold water well. Although the site was primarily wetlands with emergent grasses, sawgrass and willows, the site does not apparently retain water according to the grove manager. The third site (GFC) was selected as intermediate between the two sites. It holds water but also has a large dynamic storage capacity due to the size and shape. Unlike the other two impoundments GFC is sited on shallow rock which affects long-term retention.

Gardinier Florida Citrus (GFC)

The GFC site contains one large impoundment that has been divided into two sections, east and west. The east section was selected for this project because of the ease of access and hydrologic features; the east section has the well-defined outlet structure. The impoundment was designed to provide drainage for 1390 ac of grove. The impoundment was constructed in two lobes along the north side of the property to contain three wetlands in the eastern lobe and a large wetland in the western lobe. The site also includes a large are of uplands. The eastern lobe near the outlet is connected to a section of an old slough that ran northwest-southeast through the property. This impoundment is constructed on shallow flatwoods soils that are underlain by limestone (Fig. 7-2). This limestone is combined in placed with clay. This material which is common in the area may provide a very leaky or tight foundation depending on the condition of the limestone.

The impoundment was constructed using typical methods.  A cast levee was constructed using available materials around the designated area. Along the grove-side of the impoundment there is a borrow ditch on the outside of the levee that serves as a drainage collector ditch. There is a small ditch along the inside of the levee that serves to distribute the water inside the impoundment. On the northside of the impoundment the borrow ditch is on the inside of the levee. The section of the impoundment that connects the two lobes consists of a borrow ditch that was used to build the levee on either side. This ditch provides the conveyance canal for flow between the two sections.

This impoundment has four inflows and one outflow. The east-section of the impoundment receives discharge from the west-section through a pair of 36-inch diameter culverts. The culverts are equipped with drop structures with flashboard risers to control the flow into the east-section. There are three throwout pumps that discharge stormwater runoff from the grove to the impoundment. These are axial flow pumps attached to a diesel engine and operated using flow switches. The flow switches are set to provide approximately a foot of water removal from the collector ditches. One pump is located on the western lob and two pumps are located on the western lobe. At the East Pump and the West pump there are return-flow structures that consist of a six-foot diameter culvert drop-structure with no flashboards. These structures are required by the surface water management permit to allow flow back onto the grove to prevent damage to the levee if water gets too deep in the impoundment. Water is discharged through a pair of culverts located at the northeast corner of the impoundment. The culverts have a fixed weir.

Cooperative Producers, Inc. (CPI)

The middle impoundment of the grove was selected at the CPI grove. The CPI grove has three impoundments. The north and the south impoundments are part of slough areas and appear to contain water much of the year. These impoundments occupy low lying areas that capture runoff from the surrounding area. Consequently the groves immediately surrounding these impoundments are low-lying and require almost constant drainage. The throwout pump on one arm of the south impoundment is commonly running during the dryseason. The hydrology of these impoundments is complex. It includes capture of baseflow from the surrounding land as well as detention and storage of storm water runoff. This is more difficult situation to simulate than a simple impoundment.

The middle impoundment is a simple impoundment facility. The impoundment is approximately 93 acres and provides detention for 620 acres of grove. The impoundment was constructed on land that was a combination of freshwater marsh and flatwoods. The soils indicate that it is a flatwoods site with some shallow rock (Fig. 7-3). This site has landscape typical ofimpoundments in the watershed the site includes a marsh that is wet most of the year and a flatwoods area that has a shorter period of inundation. The impoundment is surrounded on the outside by a borrow ditch. The levees were constructed from the material excavated from the borrow ditch. The material in the levee ranges from unconsolidated sand to clay. Where there was sandy surface soil the levees are expected to have high seepage rates. The borrow ditch serves as a conveyance ditch to move drainage water to the throwout pump. There is no substantial internal ditch network. There are locations where there were ditches inside the impoundment but they have overgrown with willow and other brush.

The impoundment has one inflow and two outflow. The inflow consists a pump station that has three pumps, two 36-inch diameter pumps and one 24-inch pump with a combined capacity of 15,000 GPM discharge. There are two outlets, an offsite discharge that consists of a 36-inch diameter culvert with a 72inch circular drop-structure that has a fixed elevation edge. This discharges to a ditch that drains to an perimeter ditch. The second discharge is a returnflow structure that has the same dimensions as the outflow structure. It discharges back into the grove. The maximum storage capacity is 280 acre-feet.

Chiquita Grove

The Chiquita Grove contains four impoundment systems that are used for stormwater detention and irrigation water supply. The grove is designed to use reservoirs for irrigation water. Each impoundment system is composed of 2 to 4 cells connected in series. The first one or two cells are used as water supply reservoirs. Irrigation water from the highly mineralized Floridan Aquifer is pumped into these reservoirs and mixed with surface water pumped from the grove. There is insufficient capacity to use ground water alone.

Reservoir 4 cell 1 was selected for this study (Fig.7-4). This cell was selected because it has the best configuration for monitoring. The reservoir 4 system is used more frequently for irrigation than reservoirs 2 and 3. There are four cells in this system, cells 1,2 and 4 are used for irrigation and cell 3 is a standard stormwater detention impoundment. Cell 1 receives storm runoff from the grove via two throw-out pumps. This cell also receives groundwater. The water is released for irrigation through a screw gate. The water can flow downhill through the ditches to pump 7 and used to irrigate section 7 or flash-boards can be placed in ditch2 and the water can be redirected to pump 8 for irrigating section 8 of the grove.

Excess water from cell 1 is discharged to cell 2 through a culvert with a flash-board riser. Cell 2 is operated in a manner similar to cell 1. When both cells are full and the grove requires drainage water is released to cell 3 which is a typical storm water detention impoundment.