The Georgia General Assembly is considering a bill that will greatly affect the health of streams across Georgia. Senate Bill 460, a bill dealing with the piping of streams and stream buffer variances, has passed the Senate and is currently being considered in the House.
University of Georgia scientists have researched watersheds and streams in Georgia and the Southeast for decades. Much of this research has focused on small streams, which are the systems that will be affected by this legislation.
Senate Bill 460 proposes to allow piping of small streams with less than 25 gallons per minute (gpm) average annual flow and establishes general criteria for buffer variances. The 25 gpm average annual flow is an arbitrary number without any scientific basis.
While 25 gpm probably sounds like a small number, it’s not. An average annual flow of 25 gpm translates to over 13 million gallons per year, which could meet the water needs of over 175 people.UGA scientists are working on a study which the legislature requested when it modified the trout stream buffer legislation several years ago. The report from that study will come out this summer.
Preliminary information from this research indicates:
- In the Blue Ridge, an average annual flow of 25 gpm is generated by a watershed of about 16 acres. This only applies to the Blue Ridge. The watershed area generating that flow is likely to be significantly larger in other parts of the state. We estimate that watersheds of 30 to 45 acres would be needed to generate this flow in other parts of the state. Rainfall, topography, soils and geology all influence the amount of area required to generate this flow. These streams drain significant areas and should not be viewed as “wet weather ditches.”
- In the Blue Ridge, a stream of this size would flow in a channel approximately six feet wide and three feet deep. This includes intermittent streams that would not have any flow at some times of the year but would fill the channel during the winter and also includes small streams that begin with a spring and flow year-round.
- Often organisms such as mayflies, stoneflies and caddis flies are used as indicators of good water quality and are also excellent food for fish. In a Blue Ridge stream with 25 gpm average annual flow, there were numerous individuals from five different species in these indicator groups while in a piped stream there was only one individual in these indicator groups. In addition the total number of insects being supplied to downstream ecosystems from this piped stream was only 16 percent of what was being supplied from the unpiped stream. These insects are a critical source of food for downstream fish and other aquatic organisms.
- We have already lost considerable mileage of small streams. For example, in the Upper Chattahoochee River, tributaries draining forest and pastures have about 2.2 miles of stream for every square mile of watershed. In urban and suburban watersheds where there has been considerable piping and filling, there are only about 1.5 miles of stream for every square mile of watershed. That means that 0.7 mile of stream per square mile has been lost in these watersheds. That is a one-third reduction in stream miles in these watersheds. If only a few small streams are piped in a watershed, that will not have dire consequences for downstream ecosystems. If, however, there is a general variance with no consideration of what has been done to other small streams in the watershed, the chances for widespread destruction of small streams is great, with significant consequences for downstream flooding, water supply, water quality and fisheries resources.
This is what we know about small streams:
- They improve water quality. Think of them as the first line of defense. Excess nutrients entering waterways enter small streams, which are extremely efficient at removing those nutrients. They are much more efficient at nutrient removal than are larger, deeper channels. By eliminating those small streams you remove protection for waters further downstream.
- They maintain water supplies. There are close connections between small streams and groundwater and they serve to recharge the shallow groundwater system. Our recent experiences with drought have shown water conservation to be a critical issue in Georgia, hence it is important to maintain these services of small streams.
- They provide natural flood control. Because they slow the downstream movement of water, allow infiltration through the channel bottom to groundwater, and have access to a floodplain, these small channels reduce downstream flooding. In watersheds where small streams have been eliminated, downstream flooding increases.
- Vegetated buffers around small streams trap sediment and other pollutants, slowing their rate of movement downstream and minimizing impact to water supplies.
- They maintain biological diversity because there is a unique assemblage of organisms living in these small streams.
- They sustain the food webs of downstream ecosystems. Small streams export material that serves as food for fish and other organisms living downstream.
(Mark Risse, Judy Meyer, David Radcliffe Liz Kramer Rhett Jackson and William Bumback are scientists with water-related responsibilities with the University of Georgia.)