Water
Forms
by Jean Cutler Prior
With the puddling of raindrops, water gathers for
its innumerable journeys throughout Iowa. As it moves along,
water may become part of a kettlehole, a marsh, a farm pond, a
river, a flood, an aquifer, a fen, a cave, a spring, or a
waterfall. In all of its aspects, water adds fluid beauty to the
landscape. Both above and below ground, water is an ever-present
geologic force as well as a vital natural resource, and the focus
of environmental protection and natural resource issues.
Thousands of years ago, water in its crystalline form of ice carried the raw building materials of much of Iowa’s present landscape into the state within the grasp of massive glaciers. In turn, the melting of these glaciers laid the course of most rivers seen on today’s maps of Iowa. Even the state’s bedrock foundation, whose picturesque ledges and bluffs outcrop along some of these river valleys, originated as layers of sediment settling out of water on ancient sea floors, along coastlines, and in stream channels millions of years ago.
Iowa’s past geological environments supplied the earth materials that contain our present surface and groundwater resources. These materials shape the forms that water takes on the land surface, and they also determine how fast and how far water moves underground and where it can be tapped for wells. They affect groundwater’s natural quality, as well as its vulnerability to contamination introduced from the land surface.
Photo by Photographic Services, The University of Iowa.
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Water circulates through our environment
in a process known as the hydrologic cycle.
Precipitation from clouds falls to the ground where it
may be taken up by plant roots, flow as surface runoff to
streams, or slowly percolate deeper into the earth to
become groundwater. Water returns as vapor to the
atmosphere primarily by evaporation from lakes and
streams, and by plant transpiration. Photo by Photographic Services, The University of Iowa. |
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This shallow marsh,
with its lush aquatic vegetation, lies along the Iowa
River floodplain at Otter Creek Marsh State Wildlife
Refuge in Tama County. The sluggish backwaters persist in
broadly curved lowland sloughs that were scoured by
earlier meander channels of the river. They tend to fill
slowly with silt and clay, and are periodically disturbed
by returning floodwaters. Photo by Roger A. Hill. |
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| Photo by Dick Baker. | Photo by Roger A. Hill. |
The water in these poorly drained kettleholes accumulates from rainfall and snowmelt as well as groundwater seepage. The wetland features are a legacy of melting glacial ice 13,000 to 11,000 years ago. (Left) Freda Haffner Kettlehole State Preserve, Dickinson County. (Right) Bjorkboda Marsh, Hamilton County.
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This historic milldam was
constructed on the Winnebago River at Fertile, in Worth
County, to put the river’s flow to work. The dam
raised the river level so the force of falling water
could be used to turn wheels and stones within the mill
to grind grain into flour. Photo by Lowell Washburn. |
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A berm built across a drainageway
captures the runoff from rainfall, storing it for
livestock use. Farm ponds are
particularly abundant in the southern half of Iowa where
the rolling topography favors their construction, and the
lack of abundant groundwater resources makes these
impoundments a valuable water supply. Story County. Photo by Roger A. Hill. |
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The consistent flow of groundwater from
this column of concrete and steel at Osage Spring
Municipal Park (Mitchell County), resembles a flowing
artesian well. The site has yielded a year-round
water supply for wildlife, livestock, and people for at
least 100 years. Upwelling of groundwater can occur where
a water source, confined under pressure by overlying
impermeable rock, finds a natural opening to the land
surface or is tapped by a drilled well. This groundwater
source contains noticeable amounts of dissolved iron
(note rust-colored buildup on the column) and
hydrogen-sulfide gas. Photo by Lynette Seigley. |
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Springs occur where
groundwater flows from rock or soil material to the land
surface. This spring tumbles from crevice openings in
limestone near the entrance to Spook Cave in Clayton
County. In northeastern Iowa, springs often flow near the
base of steep-sided valleys, where water moving downward
through permeable limestone or dolomite encounters
less-permeable shale and moves laterally, finding an
opening to the land surface along a valley wall. Photo by Carol Thompson. |
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Caverns form as
groundwater moves through subterranean crevices in
limestone over long periods of geologic time. In this
scenic chamber, water seeps in along the ceiling and
slowly adds more calcium carbonate (lime) to the
glistening formations that decorate the cavern walls.
Groundwater continues to flow by gravity along the cavern
floor and down through other openings in the limestone
formation. Cold Water Cave, Winneshiek County. Photo by Michael Bounk. |
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A river is a volume of
water flowing along a well-defined channel toward some
larger (and lower) body of water. Also, in a river
channel the local groundwater table is visible as surface
water. Springs and seeps are significant contributors to
northeast Iowa rivers. Along the Upper Iowa River in
Winneshiek County, limestone bluffs overlook the channel
and provide scenic views around each bend. Photo by Greg Ludvigson. |
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During low-flow conditions along a river
channel, it is possible to see the sediments
carried by water. These rounded cobbles and
boulders are part of the load that is moved during high
flood flows along the Skunk River in Story County.
Smaller grains of sand, silt and clay can travel farther
and gradually settle as the flow volume decreases. The
capacity of flowing water to erode and deposit earth
materials makes it the most effective geological process
shaping the Iowa landscape today. Photo by Roger A. Hill. |
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The reservoir of water
in Lake Macbride (right) is separated from the Iowa River
(left) by a dam near the center of this aerial view.
Shown during flood, the muddy Iowa River is moving a
greater load of suspended silt and clay compared to the
clearer water in Lake Macbride. This reflects the greater
land area draining to the Iowa River (its watershed) and
the effects of runoff from cultivated land. Photo by Photographic Services, The University of Iowa. |
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A flood occurs when a
river overflows its banks and spreads out to cover land
not normally under water. When these Cedar River
floodwaters over Seminole Valley Park in Cedar Rapids
recede, cleanup crews will find deposits of sand and silt
as well as scoured out areas. Photo by Peter M. Schulmeyer, USGS. |
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A fen is a spongy mound
of peat fed by mineralized groundwater and supporting a
unique wetland flora. In Iowa, these "mound
springs" are typically found on hillsides. Note the
rust color as groundwater flow comes in contact with the
air, causing dissolved iron to oxidize. Silver Lake Fen
State Preserve, Dickinson County. Photo by Carol Thompson. |
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A waterfall is an
abrupt step down along a stream’s channel, usually
caused as the water drops vertically over an outcropping
ledge of resistant bedrock onto softer, more easily
eroded rock. A series of five waterfalls breaks the flow
of this Story County brook before it reaches the Skunk
River. Photo by Roger A. Hill. |