Watershed facts and figures
By GARRY BRANDENBURG
WATERSHEDS are defined as the land area where water all drains toward a central point or at a place where it ends at the junction with another drainage system. All rainfall events add water to the watershed. Not all water that falls runs off. Most of the precipitation will soak into the soil profile if the rain falls slowly enough and the soil column is dry enough to take it in. Heavy rains, sometimes described as over two inches per hour, overwhelm natural waterways, small un-named creeks and larger named creeks and it is those large rainfall events happening in short time frames that cause problems and flooding.
The Iowa River joins the Mississippi River on the eastern side of the state near Oakville. The total drainage area of the Iowa River watershed is 12,637 square miles. Its beginning encompasses land in north central Hancock County where the East Fork and the West Fork of the Iowa River remain separate systems. They join into one stream in northeast Wright County as the river flows southeasterly into southwest segments of Franklin County, then through Hardin and into Marshall.
Minerva Creek’s mouth, or point of entry, into the Iowa River is the end point for Minerva’s watershed. Land area draining into all of Minerva’s smaller streams contains 164 square miles. Stream names are not surprising with these identifiers: Minerva, Middle Minerva, Little Minerva and Little Minerva Branch. The first three join in the general area about one mile northeast of Clemons. And for a long time, for Clemons area residents and farm land owners, a big rainfall event can be cause for concern. Flash flooding has happened in the past. Only Mother Nature knows when she will pull that ace out of her sleeve and cause big time flooding again. Luckily most of the time Minerva Creek is a well behaved system. But like any stream, big or small, it will react to too much water falling too quickly within the watershed.
Water has a beginning for the Minerva watershed in northeast Story County on lands generally quite flat to slightly rolling. It is the shape of that landscape, specifically the geologic manner in which the last glacial system shaped the landscape as ice from the Wisconsinan time frame of about 20,000 years ago was at its maximum. Ice penetrated into central Iowa and went as far as present day Des Moines before an unsteady thousands of years long retreat of the ice began as the climate naturally began to re-warm.
The eastern edge of this ice mass boundary has been extensively and accurately mapped. For Marshall County, that ice margin runs north to south near the western edge of Marshall County just a few miles from the Story County line. And at two points along this ‘glacial ridge’ are the two highest points of elevation in Marshall County, separate sites, each at 1,150 feet above sea level. Because the land form slopes gently in a easterly direction, over geological time, water began to cut channels to drain the water off the land surface. Once Minerva Creek waters join the Iowa River, the landscape of all of eastern Iowa dominates as all the major rivers tend to flow in a southeast direction.
Did you know?: Iowa’s highest point of elevation is in Osceola County at 1,675 feet above sea level. Iowa’s lowest elevation is near Keokuk at just 480 feet above sea level. It is about 1,000 miles south to get to sea level in southern Louisiana. Now imagine a triangle drawn on a piece of paper in which the base is 1,000 miles long and the height of one side is just 0.09 of one mile. The angle of this slope is almost but not quite flat. But water still runs downhill, coming off every watershed.
BIRDS continue to be one of the early detectors of an advancing spring season. Mid week I observed my first of the year Red-winged Blackbird. A typical historical arrival date for this species is March 12, plus or minus. They normally depart central Iowa in mid November. Other birds to look for soon will be Sandhill Cranes. Marshall County will have a few pairs using the wetland complex of private lands northwest of Marshalltown along the Iowa River bottom lands toward Albion. Their distinctive twittering raspy call is unique. They are often heard before they are seen. Sandhill Cranes are famous for arriving in central Nebraska along the Platte River from mid March to mid April. Over 1.5 million sandhills will spend the time to rest, feed and gain the energy reserves to eventually migrate further north into Canada and Alaska. Keep watching our local Sand Lake for migrating geese of all species, ducks of all species and more Trumpeter Swans. Enjoy.
IOWA STATE PARKS will celebrate a 100 year anniversary during 2020. Iowa Public television has aired a program highlighting this anniversary. Re-broadcasts of the show will also be offered to viewers so try to become informed about these natural treasures on Iowa’s landscape. The first State Park was named Backbone because of tall limestone cliffs and scenic vistas located in northeast Delaware County. It was dedicated on May 28, 1920.
Locally it was 62 years ago when the Marshall County Conservation Board was officially begun. Three Bridges County Park was the first acquisition to provide access to the Iowa River. The name Three Bridges, as it was locally known, was because there were two small wooden overflow bridges north of the big steel frame bridge over the river. Since that time, those two small bridges have been removed due to frequent flood damage. The steel frame river bridge is now a pedestrian access for fishing. However, the park itself while only 13 acres, has its own scenic views if one hikes the trail to the bluff top. Enjoy a new Spring season soon to arrive.
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.