December 2018 Hydrology Report

Precipitation

The City of Winter Haven received an average of 6.71 inches of rainfall during the month of December. Roughly half of this total fell during a single storm event on December 20th. Compared to historic records, this was a wet month. Figure 1 illustrates how this month’s total was well above the average and about 2.5 inches above the normal range or standard deviation. Still this was far from the wettest December on record. In 1997, Winter Haven received approximately 13.5 inches of rain!

Figure 1

Since Winter Haven is a purely rainfall driven system, the net gain or loss of water can have far-reaching impacts on the lakes and water supply. One of the measurable components used to calculate the net rainfall is evapotranpiration (ET)–the loss of surface water and soil moisture through evaporation and plant uptake. Due to the cooler weather during the Winter season, ET is relatively low. Therefore, any substantial rainfall received usually equates to a net gain this time of year. With the above-average rainfall this month, the City gained 5.02 inches of water (see Figure 2). Also demonstrated in this chart is the City’s overall rainfall budget for 2018. 2017 was a dry year–which equated to a starting deficit. Despite a dry first few months, Winter Haven received a significant influx of rain during the Summer–placing the annual total at 6.59 inches.

Figure 2

Surface Level

As was mentioned above, the gain or loss of water via precipitation impacts multiple factors such as lake surface levels and groundwater recharge. The lakes in this town are such an integral component that Winter Haven was dubbed the Chain of Lakes City. By virtue of this, monitoring lake surface levels can provide insights into their overall health. Components like water quality, navigability, and wetland habitat are often directly related to surface level.

The surface level (SL) of the Southern Chain of Lakes ended the year at an average of 131.56 ft above sea level. Because this is an average over the course of the month, it may not represent the highest the lakes have risen since December 1st. As seen in Figure 3, the Southern Chain is situated between the top of the normal range (131.9 ft) and the long-term average (130.9 ft). Comparisons with rainfall during the year, there’s generally a one month lag between a substantial rainfall event and a rise in lake stage. Due to this, we can expect the average lake level to rise even higher in January of 2019.

Figure 3

Groundwater

The Upper Floridan Aquifer (UFA) is the source of Winter Haven’s municipal water supply. The level of this aquifer also impacts and is impacted by other hydrologic components such as lake levels and rainfall. The UFA under the City is monitored via a SWFWMD well located downtown. Though the actual position of the aquifer differs based on topography and underlying geology, this monitoring site is a good reference point. The average UFA level for December sits at 118.06 ft above sea level–roughly 50 ft below the surface. Figure 4 shows that the current level is just above the high end of the normal range (117.8 ft). Since there is usually a lengthy lag time between a net rainfall gain and an impact on the aquifer, we can expect this level to increase somewhat into January of 2019. Ultimately, this is a good place to end the year at from a water conservation standpoint.

Figure 4

Streamflow

The Winter Haven lakes contribute a great deal to the Peace River flows. Monitoring of the water flow it receives from the Peace Creek allows us to determine if we are effectively holding water in this region for aquifer recharge or if water needs to be discharged to meet the mandated flows and levels. The daily flow rates recorded for the Peace Creek (measured in million gallons per day) as well as daily rainfall totals for 2018 are displayed in Figure 5. During the early part of the year, flow was minimal–obviously due to the lack of rainfall during this period. However, flow peaked at the beginning of August and remained high until early October. The shaded part of the graph indicates the total volume of water during the month of August which equaled 9.7 billion gallons. Based on the City’s average annual water consumption of 2.7 billion gallons per year, this volume could supply Winter Haven’s water needs for over three and a half years! Retaining just a fraction of this volume could have far-reaching benefits for the municipal water supply. This is why the City is actively looking into long-term storage and recharge areas to capture this “well spring” during wetter months.

Figure 5