Hydrologic Report for November

12/21/2017

Hydrology is the study of water and how it interacts with the environment. This field of science is important to understand where water comes from, how it affects the Winter Haven area as well as how we, as a society, impact water resources. Hydrological changes can influence other aspects of natural resources such as water quality and local ecology in our lakes and wetlands. That is why the City Natural Resources Division (NRD) monitors hydrology as part of its overall management strategy.

November Rainfall Report

November is typically one of the driest months of the year in terms of rainfall. As Winter sets in, cooler temperatures and dry northern air limit atmospheric moisture accumulation and reduce the chances for precipitation. Consequently, it’s not unusual to see little or no rainfall during the month of November. This year Winter Haven has received 0.36 inches of gross rainfall and lost 2.19 inches due to evapotranspiration (evaporation + plant use). This deficit totaled -1.83 inches of net rainfall, bringing the Year-To-Date total down to -2.70 inches [Figure 1]. Unless Winter Haven has an unseasonably wet December, we can expect an overall rainfall deficit for 2017.

While minimal rainfall during the month of November is not out of the ordinary, the total this month did fall below the long-term average of 1.75 inches [Figure 2]. The meager amount of precipitation this month was within the normal range, however. While the lowest average rainfall for November was recorded in 1960 with a mere 0.02 inches, last year came close at 0.03 inches. In fact, it was at this point last year that we started seeing the first signs of drought-like conditions in the Winter Haven area.

November Surface Level Report

Average surface level (SL) for the Southern Chain of Lakes was recorded at 131.9 feet above sea level for the month of November [Figure 3]. This slight drop from last month shows that the lack of rainfall is beginning to have an impact on SLs in the Winter Haven lakes. Despite this, lake levels still remain near the top of the long-term normal range and capable of withstanding extended dry conditions without compromising navigability. This last year has been a bit of a roller coaster ride in terms of lake levels and the NRD is monitoring the effects these fluctuations have on water quality and vegetative communities.

Streamflow

The lakes of the Winter Haven area make up part of the headwaters to the Peace River—in association with Lake Hancock and some waterbodies in southeast Lakeland. Many of the lakes, especially those in the Chain of Lakes have connections which flow to the Peace River via the Peace Creek. Figure 4 (on the next page) depicts these connections and flow ways as well as the path this water takes as it makes its way to the Peace River and eventually to the Gulf of Mexico.

Hydrologically, Winter Haven is a rainfall driven system—meaning that it relies on precipitation as opposed to rivers or streams for water inflow to the area. The challenge in managing this system is to allow enough water downstream to prevent negative impacts to the Peace River and Charlotte Harbor while simultaneously preserving enough water in the area to replenish the aquifers from which we extract drinking water. Control structures at Lake Hamilton and Lake Lulu regulate the amount of water that leaves the area. Flow to the Peace Creek is monitored using flow meters (shown in Figure 4) and is regulated by adjusting the control structures mentioned above.

November Streamflow Report

Since streamflow (SF) hasn’t been covered in this report before, this month’s section will be looking at the overall trends in flow throughout 2017. Flow data is taken from a hydrologic sensor on Peace Creek (near Bartow) which represents aggregate SF from all of Winter Haven’s lakes. Minor, sporadic rainfall events in the first half of the year correspond with a slight decline in flow from January until June (Figure 5). The SF begins to pick up after the first major storm events in June and eventually peak at over 500 million gallons/day (MGD) after Hurricane Irma—roughly the volume of Lake Shipp.

To further put this amount of flow into perspective: the shaded area on the graph equates to about 15 billion gallons over a 60 day period. At current municipal consumption rates of ~10 MGD, that volume of water could supply the City for 1500 days or just over 4 years! If the City can strategize holding more water from these events in the area and allow it to recharge the aquifers, it could help solve future supply issues.

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