2020 Summer Newsletter Rainwater-Our Valuable Resource! Have you ever noticed the soothing feeling that you get when you look out the window at the rain and hear the the sound of the raindrops falling gently on the leaves? There is a current clip on TV that features rain falling on leaves with the words “do nothing for fifteen seconds” that produces the same effect. The calming effect of rainfall is just one small way that rainfall is valuable. Rainfall is also valuable as an important part of the hydrological cycle of the earth’s water and replenishes our surface and groundwaters. There are 326 million-trillion gallons of water on our planet. Less than 0.03 percent of that water is fresh water and two-thirds of that is tied up in ice and glaciers. This means that our freshwater resources are extremely limited and should be used wisely. We need to try and reduce our water footprint, which is the amount of fresh water used to produce or supply the goods and services we use. If you want to get an idea of what your water footprint is, read the article below and go to www.watercalculator.org and click on the water calculator. Not only do we need to conserve our use of freshwater but we also need to understand and respect rainwater in its role as stormwater and the devastating effects it can produce with flooding and the pollution it carries into our streams and rivers. Different regions receive varying amounts of rainfall annually. For instance, about 39.6 inches of rain fall on Akron yearly and it rains an average of 157.6 days in the City. Did you know that six gallons of water fall into one square foot of land during a one-inch rainfall? A one-acre plot of land would receive 27,154 gallons in that same one-inch rainfall. If the acre of land is in a forest, that rainwater would be absorbed and soak into the forest floor where it fell. The forest soaks up nine times more stormwater than suburban and urban areas can with their paved surfaces, roofs, and turfgrass lawns. What happens to all that excess stormwater in a place like Akron with all the impermeable surface area? The answer is that it becomes stormwater runoff and goes directly to the stream or river, via the storm drain, carrying with it all the pollutants that it picks up on the way. When the stormdrains and underground infrastructure can’t handle any more stormwater, we have flooding and the destruction that it causes. In a city like Akron with its combined sewer system, we have sewer overflows and raw sewage ends up in the Cuyahoga River. Akron Waterways Renewed is currently working on a massive project to rectify flooding and sewer overflows. We don’t have to have flooding and disasters if we plan wise management of our stormwater. Do you know how many inches of rain are in a 10-year rainstorm event, or if a 10-year rainstorm event will cause local flooding? Most of us rely on our local Summit County stormwater professionals to keep track of this information and use it to design practices which improve water quality and reduce flooding in our county and region. Now is a good time to focus on rain and explore some of the rainwater statistics that we often hear about but may not understand fully. Well-informed individuals make better decisions regarding the incorporation of measures that affect our communities’ stormwater infrastructures. Storm events are measured in the amount of rain falling during a period lasting a prescribed number of hours and relate to the probability of the event occurring again in a certain time span, say for instance, 10, 25, or 100 years. For estimating rainfall events, hydrologists, (scientists who study the movement, distribution, and quality of the water on earth and other planets,) use “return periods.” A return period is an estimate of how long it will be between rainfall events of a given magnitude in any given location. For example, the return period for a 3-hour rainfall with a total of 4.25 inches in a certain city is 25 years. This means that, on the average, a 4.25-inch rainfall lasting three hours occurs in that city once every 25 years. Of course, this information is based on statistics and there is no guarantee that once you have had this much rain, you won’t get it again for another 25 years. If you had 100 years of records, there should be four such rainfall events (an average of one every 25 years.) These events could be in consecutive years or even multiple events in a single year, and there is also no guarantee that a nearby location will not experience such an event. Each county in Ohio has a slightly different amount of rain in a 10, 25, and 100-year storm event. Generally, the farther south you travel, the more rain you can expect to receive. In Summit County, a 10-year storm event would produce approximately 3.4 inches of rain, a 25-year event would yield 4 inches, and a 100-year event would have a 4.4-inch rainfall, all in a 24-hour period. Storm events are different from flood events. A 100-year storm will not necessarily create a 100-year flood. A rainstorm event is more localized and a flood event is more regionalized. The size of the area involved makes a great deal of difference. For instance, a 100-year storm in a small drainage basin or watershed of about one square mile would have a much greater effect on streamflow than the same storm in a 50 square mile basin. The term “100-year flood” is misleading because it leads people to believe that the flood happens only once every 100 years. A huge flood can happen in any year, even though it is less likely to. The term “100-year flood” is also a statistical designation and it means that there is a 1 in 100 chance that a flood this size will happen during any year. The actual number of years between floods of any given size varies a lot and big floods happen irregularly because the climate naturally varies over many years. A general rule-of–thumb for stream flooding is that a 3-hour rainfall total exceeding the 10-year return period is likely to cause some flooding. Whether or not a stream floods from the given rainfall amount (or less) is dependent upon factors other than rainfall amount. Some of these factors are surrounding soil moisture, prior stream stage, (bank-full or floodplain spreading,) whether tributaries are already near flooding, amount of urbanization (impervious area), and basin and channel characteristics. Floods are part of the natural cycle of every river and stream and benefit stream habitats by moving material downstream and renewing streambeds. As floods get bigger and spread farther, flood waters slow and deposit sediment on the floodplain. This natural process had created many fertile farmlands over the years. Remember the “Fertile Crescent” of the Tigris and Euphrates Rivers in our history books! But the character of Ohio’s rivers, streams and ground water has changed greatly over the last 200 years due to human activities. Forests and prairie lands once kept our streams narrow and deep by holding the banks intact, and stream water was cooler and cleaner with a great diversity of species depending on it for life. The changes we make to each watershed or drainage basin’s land use, changes the character of our streams. Agricultural fields and suburban lawns are often planted right up to the edge of the stream banks. This eliminates buffer or riparian zones which would slow down and filter the water. The loss of trees and their streambank root structures allow streams to run wider and shallower, causing sediment to be deposited and silt-over important biological habitat in the stream. Sediments and pollutants must be filtered from the water before it is used for drinking and other uses. Millions of dollars are spent each year for dredging sediment from channels, harbors, and reservoirs. Urbanization increases impermeable surfaces, streets, roofs, and parking lots. Our streams receive greater amounts of runoff and the pollution that is carried with it over these land surfaces. Many streams have been straightened to allow water to flow faster. The increased runoff results in streambanks and beds being scoured with resulting erosion and sediment loss. Downstream flood damage also increases as streams carry more water at a faster rate. The importance of watershed-based land use practices cannot be overestimated if we hope to restore our streams and rivers to some of their former health. Our stormwater professionals use rainstorm statistics to help them design practices which will reverse some of the damage to our streams as a result of urbanization. These engineers and other stormwater specialists will also be using these facts to help them design practices that will prevent future damage to our streams and rivers. We as residents of Summit County can aid these efforts by remembering that our land use activities affect our stream environments and by making a conscious effort to engage in responsible watershed stewardship. For more information on healthy watershed practices, call Summit Soil and Water Conservation District at 330-926-2452, or go to the District website, http://sswcd.summitoh.net References: ODNR, USGS, Oklahoma Climatological Survey, USDA/NRCS, OSU Extension Service, Muskingum SWCD, Hamilton SWCD, Clermont SWCD, Medina SWCD, National Groundwater Association, BBC Future Now.