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August 2018 Hydrology Report

Posted September 6th, 2018

August 2018 Hydrology Report

Averaging the data from 8 precipitation gauges scattered across the City, the Winter Haven area grossed 7.41 inches of rainfall during the month of August. Since Winter Haven is a rainfall driven system, it is important to quantify the net rainfall gain (or loss) as this impacts aspects such as lake levels and aquifer recharge. Water loss through evaporation and plant uptake (evapotranspiration) is subtracted from the gross to calculate net rainfall for the area. Total evapotranspiration for August was 5.11 inches, which translates to 2.3 inches of net rainfall for the month. Tallying the monthly net rainfall totals in 2018, this is the second month this year with a net rainfall gain which raises the Year-to-Date surplus to 4.67 inches—see Figure 1.

Figure 1

Compared with historic records dating back to 1915, this month’s gross rainfall has been right at the monthly average for August—See Figure 2. In conclusion, the surplus rainfall this time of year should continue to contribute to aquifer recharge and maintenance of high lake levels.

Figure 2

Surface Level
The average stage of the Southern Chain of Lakes saw a considerable increase from 131.65 feet above sea level in July to 132.26 feet in August. Figure 3 shows that the average lake stage continues to rise at a similar rate to last month in response to heavy rainfall patterns. With a monthly average surface level above 132 feet, the Southern Chain is contributing substantial continuous flow to the Peace Creek.

Figure 3

Compared to historic data, this August’s average lake stage falls well above the upper limit of the normal range (131.78 feet) and has just about reached the maximum average lake stage in the period of record for the month of August (132.28 feet). With the lakes this elevated, the risk of flooding continues to rise as we move through peak hurricane season. The City will continue to monitor SLs and keep open communications with the Water Management District in the event that increased discharges are required from the Winter Haven Lakes.