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Base flow keeps some water in the river

September 14, 2013
By GARRY BRANDENBURG , Times-Republican

WATER is precious. All living things, plant or animal, need it. Without it we die. Without water plants also become stressed to the point where some may not live through it. The saving grace for native grasses, forest lands and agricultural crops is the water the soil can hold within its profile, even if deep down and hard to acquire. Plants have roots and special tap roots that will grow to almost any level to find moisture. It is not ideal, but life hangs onto this thin thread. Many plants are adapted to dry conditions by turning off their functions via a term we call dormancy. Area lawns are just one example of dormancy, a survival technique to retain plant life within the root system instead of above ground. Given enough new rain, the surface leaves will respond with a new burst of photosynthesis.

BASE FLOW is the name adopted to what we see in area streams and river. The water in the river is flowing even if it is a mere trickle compared to "normal" or certainly compared to the maximums of flood time crests. Think of it this way. Take a sponge and soak it thoroughly with water. This is equivalent to the soil profile being saturated, i.e. all the pores are full of water. Lay the sponge outside on a hard surface where wind and sunlight have access to the sponge. Water will leak out of the bottom of the sponge as it dries from the top. If the top surface is dry, pick it up and note that the bottom is still moist. Give it more time and it will completely dry out.

One can prolong the drying process by adding a thin cover over the top of the sponge. That cover is representative of crops growing on ag lands, forested areas, and grasses of pastures or native prairie lands. Drying will take longer, but there still remains transpiration of water out of the plant's leaves via evaporation. Plants adapt to hot dry weather as best they can by rolling leaves to reduce surface area. Trees that are well established hunker down for the long haul in their quest to survive.

Article Photos

T-R PHOTO BY GARRY BRANDENBURG 
Sandbars help define the river bed of the Iowa River in this segment downstream from the Highway 330 bridge near Timmons Grove. West is at the top of this image, east is at the bottom. Since we have had virtually no rain for more than two months, there is no surface runoff of water into the river. The small amount of water that is flowing comes from base flow, the geological term for the slow yet steady seepage of water out of the surrounding land’s water table. At this point, canoes or kayaks might not be able to find enough water to float the river. This image was made Thursday.

River base flow, or groundwater discharge into streams, is maintained when groundwater levels are still a tad higher than the stream bed itself. Small streams may actually stop flowing or appear to dry up entirely. Add a bit of rain, or the approach of fall seasons when plant water needs diminish, and visible flows of water will return. The amount of base flow a stream receives is closely linked to the permeability of rack or soil in the watershed. As an example, the Floyd River in northwest Iowa moves through a watershed composed of clayey glacial till and silty loess. Based on a 12 year record of stream gauging from 1987-1999, each square mile of land in this watershed produced an average of 3.7 inches of base flow discharge.

Contrast this to a northeast Iowa stream, the Upper Iowa River, which flows through a watershed of fractured limestone and dolomite. Flow rates here averaged 8 inches per square mile during this 1987-1999 time frame. Our Iowa River in Marshall County is somewhere between these research data figures. Right now the Iowa River is flowing at 8.93 feet of stage, or 862.03 feet above sea level. On Aug. 1, it was at 10.71 on the measuring gauge or the equivalent of 863.81 feet above sea level.

Such low flow rates do have an effect upon the health of living organisms within the stream. Aquatic organisms are part of the food chain that feeds everything from the smallest of fishes to the larger predator fish or other predators above the water. Base flow water does tend to be rather uniform year-round thus adding temperature stability to stream waters. The relationship between surface water and groundwater during base flow periods helps define water quality issues, a pertinent topic in a state like Iowa that is so highly agriculturally oriented. Base flow water samples do help scientists understand and identify local sources of pollution. Policies to address common sense solutions to pollution sources will be an ongoing situation in Iowa.

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Last week, low water inside the lake at the GREEN CASTLE Recreation Area was the setting for a youth fishing event. Kids under 16 were encouraged to attend and be available for prizes. In spite of the heat of the day, 32 kids did turn out to try their hand. The largest fish was a bass measuring 12 3/4 inches long hooked by Braylee Kimberly. Caleb Reece landed the smallest fish, a 3 7/8 inch long crappie. The most fish taken was 15 by Braylee Kimberly. Random drawings during the event went to any youth that registered, fish taken or not. It was fun. While at Green Castle, ongoing shoreline and fish habitat structures were visible for inspection. The thing to remember about working with Mother Nature at a lake such as this is her time factor. Dry weather is the ideal time to do the work with heavy equipment. Wet weather will return soon enough and when it does, the hard work of fish management is already in the books.

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Iowa's first YOUTH DEER HUNTING SEASONS begin next Saturday, Sept. 21. That day also marks the start of DISABLED HUNTER times. Youth deer season is open statewide for anyone age 15 or less in the company of a mentor to provide one-on-one advice. In 2012, nearly 9,700 youths and 290 disabled hunters took more than 3,900 deer. A disadvantage of early seasons is temperature. A cool down in air temps is expected but late September is still a late summer mode concerning the weather. If a deer is taken, it must be quickly cleaned and cooled to preserve the meat. Arrange for an early taken deer to get to a locker plant as soon as possible. State Center's Locker is just one local business to take deer to. Remember that all deer must be registered with the Iowa DNR via a simple to use confirmation system of phone or computer.

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The Marshalltown CITY URBAN DEER BOW HUNT also begins Sept. 21. More than a dozen archers are qualified to hunt somewhere within the city limits. Terry Gray at the Parks and Recreation office can try to match a hunter's need for access with a hunter's desire to assist in the deer population control effort. Property owners that wish to cooperate in this endeavor may contact the Park and Rec office at 754-5715. Marshalltown's urban deer control program is one of 56 special city, suburb or state or county park areas where special hunts for deer are allowed. These are in addition to the regular early muzzle loader, shotgun, archery and late muzzle loader seasons throughout the state.

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OCTOBER is not that far away sportsmen and ladies. Mark your calendars now for Sporting Clay Shoot at the Marshall County Ikes on Oct. 6. The proceeds of this shoot will be a fundraiser for Iowa River Hospice. Ten stations, 100 birds for a fee of $35 will apply. Food will be provided by Mr. G's for modest costs.

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Oct. 19 will be the date for this year's PHEASANTS FOREVER banquet. It is hosted by the combined chapters of Tama and Marshall counties. The activity and fundraising will be held at the Marshall County Fairgrounds. Doors open at 5 p.m. Advanced ticket sales are the way to go. Call Steve Armstrong at 641-751-1668. A single adult ticket includes the banquet meal and a one year membership in PF for $60. At the door tickets will cost $75 after Oct. 14.

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Biological factoid: Research shows that a healthy white-tailed deer herd, reasonably sized to make the most of available habitat, can be reduced by as much as 40 percent with no ill effect on the future population. Left alone, a deer herd with no hunting at all, will double in two years. Two years later it would double again, striping available food sources of all kinds. Proper management is required through well regulated hunting seasons. Hunting is conservation.

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Garry Brandenburg is a graduate of Iowa State University with BS degree in Fish & Wildlife Biology. He is the retired director of the Marshall County Conservation Board. Contact him at PO Box 96, Albion, IA 50005.

 
 

 

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