RAINWATER DISPOSITION IN THE BONITA BAY COMMUNITY (BBC); PART OF THE WATERSHED OF THE CITY OF BONITA SPRINGS
Introduction:
Rain is the result of precipitation from cloud water droplets which condense in the atmosphere. When these water droplets get too heavy to stay suspended in the cloud they fall to Earth. Management of this precipitation is critical to survival of individuals and communities in SWFL. The example presented here is similar to most of the west coast SWFL communities except for an interesting variant called a slough. The dominant measures used in this water control are nearly 70 retention ponds, strategic use of the marsh land, and proximity of the two rivers. This monograph provides a description of a typical residence (Fig 1) in the Bonita Bay Community. Rain on the roof flows through a mandated roof line gutter system down to an underground water diversion system and then to the neighborhood community retention pond at the back of the house. Street gutters also flow to sewers that are connected to the retention pond. The pond is a constructed extension of the central slough marsh. At the northern terminis of the pond there is a weir that controls overflow from the pond to the slough. The slough is a natural part of the otherwise engineered water system of the Bonita Bay Community. In this specific neighborhood, the water in the slough flows southward 450 ft through a volume-controlled water weir to the Imperial River. This river flows west to Fish Trap Bay which in turn is part of the Estero Bay on the Gulf of Mexico. The following maps show the property boundaries and water flow through the Bonita Bay community. Maps are from the EPA
The featured image is a view of a portion of the slough connecting the Imperial River and Spring creek. It is not picturesque however it is important. This is the status 10 months after the flood surge of hurricane Ian. The photo was made viewing south of the image shown in Fig 8 of this posting. It seems to show more damage than the opposite view. This may be the result of salt water standing longer in this area which is the water is very slow moving perhaps because it is trapped from flowing to the south at at the Imperial river and it is a long distance to flow to the north to Spring Creek.
Figure 1 Residence with roofline gutter system and downspouts
Cartography:
Fig 2 shows an overview of a portion of the city of Bonita Springs. This area is bounded by the Imperial River to the south, Spring creek to the north, highway 41 to the east and Estero Bay to the west.
In addition to the rivers bounding the property there are additional features which are part of the water flow as seen in Fig 3. Note the centrally located non-tidal marsh slough that is oriented north to south connecting the two rivers. This slow-moving marsh water is a naturally occurring body that is an often ignored but dominant and important feature in the community.
Figure 3 Water flow system of the Bonita Bay Community. The red square is the approximate property line.
The location of the residence relative to the nearby Imperial River is seen in Fig 4. The distance of the residence to the river is 450 feet. The house is directly on the east side of the water retention pond.
The water flow is shown in Fig 5 for this neighborhood portion of the BBC of the City of Bonita Springs. Note that the residence is not only near the Imperial River, but also the water retention pond. The pond is also part of the central, non-tidal, slough that transepts the whole Bonita Bay community.
The water retention pond with a weir on the northwest end is seen in Fig 6. Another weir is at the river. Water is normally lost from the retention pond through transevaporation. When water in the pond is high the overflow is directed to the slough through the overflow weir.
The slough is a marsh with reeds and sedges compromising most of the plant life and supports birds, reptiles and mammals. The entire slough and land close to the rivers and the Estero bay were completely covered by approximately 5 feet of oceanic sea water. All of the soil is still ladened with salt residue. There has been less than 6 inches of rainfall in the last 9 months. During that time there have been only three days of rain sufficient to cause some runoff through the local weir. Hopefully the seasonal rain water will dilute some of the salt every year and it will be carried back to the ocean.
The relative elevations of the Bonita Bay Community in Bonita Springs are seen in Fig 9. The legend indicates that most of the community is at 5 ft +MSL. Note the approximate watershed divide.
Discussion:
The water flow is generally toward the sea. The river and creek are tidal therefore it is bi-directional depending on the tides, rainfall, storm surges and other upstream water flow. The non-engineered mean elevation of the community is 5 ft +MSL. There are four water sources for the BBC that include, freshwater brought by the city to the community, grey water brought to the Community for irrigation, and rainwater during the rainy season and salt water during storm surge. The community looses water through three methods. these include transevaporation, runoff and sewage. Sewage water from residences exits through sanitary sewage lines to the central water treatment plant. The central high ground is the location of the club house. The purple line drawn horizontally through the high ground indicates the approximate north/south watershed divide. The average elevation of the property is less than two feet above the sea level where salt water begins to invade the low-level properties or displace the less dense freshwater. The property was designed more than 35 years ago and has worked well. Since then, hydraulic pressure from the rising waters of the sea have increased. Fresh rainwater is a valuable resource. Considering our changing sea water level perhaps some questions should be addressed. Do we need to rethink the water flow design? Should we consider an alternative method for disposition of rainwater through different conservation measures? Can we conserve fresh water and delay ingress of salt water?
Conclusion:
The rainwater may be distributed up-stream and down-stream once it meets the estuary/river, but generally it flows down to the Gulf of Mexico. The low elevation of the property and other weather factors determine the rate, volume and direction of flow.
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#slough #waterflow #watershed #marsh #creek #river #rain #transevaporation #seawater #
Little did I know. I thought they were small freshwater lakes.