The Flow of the Wekiva River
Current Stream Flow In Wekiva River Ben Franklin once said, “When the well’s dry, we know the worth of water.” In my opinion, this quotation illustrates the importance of studying and understanding a river’s flow. Many do not realize that the ecology of a river depends completely on the level of the river. Also, extremely high or extremely low levels may affect the health of humans, such as in the case of nitrate poisoning. The St. Johns River Water Management District has effectively implemented ways of measuring flow and levels of the Wekiva River as a form of conservation as well as prevention from illness. It is important to remember that most of the Earth’s water is in the oceans and seas, leaving only about three percent left for the hydrologic cycle. Almost eighty-eight percent of the available fresh water is in the form of ice caps and glaciers. Only a fraction of one-percent of the Earth’s water is liquid. This is just another reason why we should understand the importance of monitoring all aspects of out limited fresh water supplies, especially here in Florida.
The Hydrologic Cycle
Before we are able to understand flow and its importance, it is essential to understand a bigger flow cycle. The hydrologic cycle is a closed system of water. Water cycles through its different phases, from liquid to gas and back to liquid. The cycle is powered by the sun and is responsible for initiating evaporation. Once evaporated, the water exists in the atmosphere as clouds and vapor. When the right conditions are present, the water changes state and falls as precipitation. Precipitation that reaches the land has a variety of different pathways it may followl. Some will flow on the surface as runoff and end up in a body of water. Some will seep into the ground and, through a process known as infiltration, will percolate down through the soil. Moisture that is not absorbed by plants and soil continues to seep down into the water table. Water that accumulates below the water table is more commonly known as ground water. Most ground water flows beneath the land surface until it reaches a point of discharge, such as a spring. The hydrologic cycle, however, doesn’t account for the water that is added to the cycle.
One source of this additional water is volcanic eruptions within the earth. These eruptions add very small amounts of water to the hydrologic cycle each year. This added water that is removed from the cycle balances water. The hydrologic budget is a quantitative description of the total water gained or lost from an area in a specific period. In other words, the water budget balances water gained from different sources with water lost, P(t) + I(f) = E(t) + O(f) + C(u). The water gained in an area would come from precipitation (P(t)), and any inflow (I(f)) from adjacent areas. Water is lost through evaporation from land and the surface of bodies of water and through evapotranspiration , that is, water that plants absorb from the soil through their root system and release as water vapor (E(t)). In addition to evapotranspiration, scientists account for outflow from other areas, (O(f)), and consumptive use, (C(u)), the water withdrawn by humans for activity and is not returned to the cycle. Also accounted for in the equation, but not represented in this formula is the addition or subtraction from outflow to show the losses or gains in total amount of water stored in the system as surface water or ground water.The global version of the hydrologic cycle may also be applied to the cycle in Florida; however, Florida’s system is not a closed system. Florida’s hydrologic cycle includes the inflow of surface and ground water from Georgia and Alabama into northern and northwestern Florida. However, in central and southern Florida, rainfall is the only ultimate source of fresh water. Much of the water that is precipitated in Florida is recycled directly back into the atmosphere by evapotranspiration. In Florida, daily average evapotranspiration is estimated to be about 110 billion gallons. Stream flow variation in Florida is unusual for a couple of reasons. First, month-to-month variation is relatively small. Another reason lies in the fact that the seasonal variations of streams in different sections in the state are different. This variation may be attributed to four factors: the relatively low variability of average monthly rainfall, the high rate of evapotranspiration in summer, the large volume of slowly released natural storage in Florida’s numerous lakes, and the large and stable inflow of ground water to streams from the extensive and unique aquifer system.
The Floridian Aquifer
The state of Florida is underlain by one of the most fertile aquifer systems in the United States. Our aquifer also extends into portions of Georgia, Alabama, and South Carolina. Discharge from the aquifers in Florida occurs in many ways. Water flows from shallower aquifers to the Floridian and vice versa, depending on the hydrologic conditions. Aquifers discharge to surface water through springs and seeps to areas such as the Gulf of Mexico and the Atlantic Ocean. A Florida specific water balance equation was derived from studying annual inflow and outflow of water. Scientists used an average rainfall figure of five inches, which is equal to one hundred fifty billion gallons of water per day when measured over the entire state. They estimated inflow of surface and subsurface water from Georgia and Alabama at an additional twenty-five billion gallons a day, for a total inflow of one hundred seventy-five billion gallons a day. Their estimated outflow figures are sixty-five billion gallons a day for outflow of surface and subsurface water and thirty-eight inches per year average evapotranspiration for the state, giving approximately one-hundred seven billion gallons a day. Their equation is, in billion of gallons a day, 150 + 25 = 110 + 65, where inflow equals outflow.
Surface Water
Surface water is one of the most familiar and accessible supplies of fresh water. The water leaving a drainage basin in the form of surface water is called runoff and comes from groundwater and precipitation. The groundwater contribution to runoff can come from springs or seepage into a stream channel. This contribution to stream flow is known as base flow and is the reason some streams continue to flow even though the drainage basin may be experiencing an extended period of low rainfall. Precipitation falling on a drainage basin contributes to runoff through several pathways. Water reaching the ground can form puddles, flow overland as a thin sheet of water, infiltrate the soil, or fall onto the surface of lakes and streams. Water in puddles eventually evaporates or infiltrates the soil. Overland flow occurs when the precipitation rate exceeds the rate at which water can infiltrate the soil or when the soil layer becomes saturated. The flow record of a stream will reflect the discharge contributed by direct precipitation, interflow, and overland flow. Variations in stream flow resulting from changes in base flow occur more gradually than short-term variations caused by precipitation inflow.
Water is a river’s most obvious and essential component. Instream flow refers to the water in a river’s channel. In a healthy river, water levels fluctuate naturally. Flow is cyclical varying greatly on a time scale of hours, days, years, decades and longer. Flow also varies from place to place, depending on regional differences in climate, geology, and vegetation. It shapes the river, defining the size, location, and course.
All native plant and animal lives, in and around a river, are adjusted to and dependent upon, the normal, seasonal, and year-to-year changes in the flow and level of the stream. Without a certain amount of water flow or a particular level of water, at the right time and for a sufficient duration, reproduction and growth of fish and other water-dependent animals or plants could be inhibited. Flows in a river are measured in cubic feet per second (cfs) and levels are measured as feet above mean sea level (ft, msl). According to state law, minimum flow levels (MFLs) are the flow or level at which further withdrawals of water would be significantly harmful to the water resource itself or ecology of the area. MFLs are set as a guide for water resource and water supply development to guarantee water resource sustainability for people and environment.
Measuring Flow
The flow and level of the Wekiva River are measured in various locations along the river by gauging stations. These stations are responsible for making the systematic observations and collecting the hydrologic data. The gauges in a river measure the stage of a river at a specific location. Using the equation, Q = VA, where Q is flow, V is velocity, and A is area, the gauging stations and engineers are able to come up with specific measurements. A control is set up downstream from the gauging station to help develop standards that can be used as a comparison to the data collected by the gauging station. This control determines the stage-discharge, the relation between stage (gauge-height) and the volume of water per unit of time (discharge) flowing in a channel at the gauge.
Establishing Minimum Flow Levels
Florida’s Water Resource Act is somewhat based on a Model Water Code. This code was written with the purpose of developing a water management system at the state level that accounted for the hydrologic relationships between all water resources and allowed an integrated approach to water quality and quantity issues to be implemented. Among its requirements, left up to the state board, are minimum flows for all surface watercourses. The minimum flow should be based on the limit at which further withdrawals would be harmful to the water resources and ecology of the area.
The St. Johns River Water Management District (SJRWMD) has completed their adoption of minimum flows and levels for the Wekiva River Basin, which also includes the Upper Floridian Aquifer. SJRWMD recognizes that water levels and flows fluctuate seasonally and overtime in all systems. High, low, and average flows or levels serve important functions; therefore, the district compensates for this in the setting of the levels. They establish the minimum level as including a water level, and a minimum hydrologic statistic for that level, such as frequency or duration. SJRWMD technical staff assesses each water body or surface watercourse by examining any hydrologic records as well as examining in the field, soils, geomorphology, and biology, associated with the system. After their analyses, the staff performs a scientific evaluation to determine appropriate minimum levels and/or flows, with the goal of defining the minimum hydrologic regime that must be maintained to prevent significant harm to the watercourse. Each of these standards is represented by a level (in feet), a flow (in cubic feet per second), duration (in days, and a return interval (in years). The multiple levels form a minimum stage-duration curve, which defines the percent of time a waterbody meets or exceeds a range of water levels.
Reasons for MFLs
One reason minimum flow levels have been established is to prevent humans as well as animals from suffering from serious health problems. Nitrate poisoning is one such cause of health problems as a result of low flow levels. Nitrate is an organic form of nitrogen found in soil. It is essential for all life and large quantities of nitrogen are essential for crops to produce high yields. The formation of nitrates is an integral part of the nitrogen cycle in our environment. In moderate amounts, nitrate is a harmless constituent of food and water. Plants use nitrates from the soil to satisfy nutrient requirements and may accumulate nitrate in their leaves and stems. Due to its high solubility, nitrate also can seep into groundwater. Nitrates form when microorganisms break down fertilizers, decaying plants, and manure. Plants usually absorb these nitrates, but rain and irrigation water can also move them into groundwater. Nitrate occurs naturally and is commonly found in some groundwater; however, higher levels may be attributed to human activities. High nitrate levels in water can cause methemoglobinemia or baby blue syndrome, a condition found mostly in infants less than six months. The stomach acid of an infant is not as strong as that of an adult and can therefore cause an increase in bacteria that converts the nitrate to nitrite. It is recommended that infants do not consume water with nitrate levels that exceed 10mg/l. Nitrite is absorbed in the blood and the oxygen carrying component of blood, hemoglobin, is converted to methemoglobin. Methemoglobin does not carry oxygen efficiently and results in reduced oxygen supply to vital tissues, such as the brain. Severe methemoglobinemia can result in brain damage and death.
High levels of nitrate in groundwater can also affect the health of animals. Unlike for humans, there is not an enforceable drinking standard for livestock. Animals should not consume water with nitrate levels more than 100mg/l. This is especially important for young animals because they are affected in the same manner as human babies. In addition to groundwater, nitrate also exists in animal feeds. Plants affected by drought commonly have high nitrate levels. These feeds can have an additive effect when consumed with high nitrate drinking water.
Ben Franklin once said, “When the well’s dry, we know the worth of water.” In my opinion, this quote illustrates the importance of studying and understanding a river’s flow. Many do not realize that the ecology of a river depends completely on the level of the river. Also, extremely high or extremely low levels may affect the health of humans, such
Problems in Wekiva River and it’s Branches
Heavy rains cause stormwater to flow through ditches and canals and into the Little Wekiva River. With it, it brings pollutants and sediment that erode the banks and bottom channel of the river. The buildup of sediments has caused frequent flooding and deterioration of water quality in the Little Wekiva and Wekiva Rivers. The Little Wekiva River has a history of problems including: an increase in the rate of flow and velocities as a result of the area’s urbanization, minimal upstream stormwater storage and treatment due to much development occurring before current stormwater conditions, erosion and flooding which cause public safety concerns, and adverse environmental and water quality impacts from the movement and deposit of sediments. The St. John’s River Water Management District is working with the Florida Department of Environmental Protection, the Florida Department of Transportation, the city of Altamonte Springs, Seminole and Orange counties, and environmental interest groups and residents of the area to develop a basinwide approach to these problems. Among the goals for the project are creating and building structures to protect river banks and beds, widening and revegetating channel sections, installing grade controls to stabilize river bed slopes, and monitor and evaluate needs based on the dynamics of the river system.
Conclusion
It is important that this type of action by the State of Florida is starting to take place. It illustrates that the government as well as public is becoming aware of the importance of monitoring the Wekiva River. Keeping track of flow levels allows experts to know when the river is at a dangerous level and they can then inform the public. However, that information to the public does not do any good unless they understand the terminology and how they may in turn be affected by it. I hope the public learns to appreciate the Wekiva as Bill Belleville has put it on one of his many accounts of the river: “By night, the Wekiva seems as if it has reclaimed its historic territory once again, becoming a jungle where one can truly lose him- or herself, can even, in fact, get wonderfully lost. In appreciation, we put our paddles on our laps and drift wordlessly in the gentle current, like a very large leaf on a rill, letting the whims of the nocturnal river carry us into the subtle romance of the river night.” (River of Lakes, pp. 74-75)