Hydrogeology

The bedrock of the Mud, Camp, and Spring Creek Watersheds consists of marine sedimentary rocks, including: sandstones, shales, mudstones, limestones, and dolomites. These rocks were deposited during the Carboniferous period, 354 to 290 million years ago. This period was further divided into two times periods: the Mississippian and the Pennsylvanian. Shallow seas covered the Midwest during the Mississippian and deposited clays, sands, and carbonate materials. The seas receded, allowing water and wind to erode the surfaces of the Mississippian rocks. The seas returned and again receded during the Pennsylvanian. For much of Polk County, Pennsylvanian bedrock is found (Polk County Comprehensive Plan, URS, February 2005).


According to an Iowa Department of Natural Resources (IDNR) geological survey completed in 2008, the depth to bedrock in Polk County ranges from less than 50 feet to over 200 feet to the bedrock.


Rainfall

Annual precipitation in the state of Iowa averages approximately 33 inches. However, precipitation is highly variable across the state and averages have been recorded in areas as little as 20 inches per year to as much as 47 inches per year. Figure 2-23 displays the variability of the average annual rainfall in Iowa.

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Ankeny, Iowa is located near the Mud, Camp, and Spring Creek Watersheds and averages 33.88 inches of rainfall per year. Figure 2-24 depicts the variability of annual rainfall totals at the Ankeny Regional Airport. The gage at the Ankeny Regional Airport recorded over 50 inches of annual rainfall in the years 1993, 2008, 2010, and 2012 with the largest yearly rainfall in 2012 recording 59.92 inches. Table 2-2 ranks the top ten recorded daily rainfalls at the Ankeny airport between January 1951 and December 2015.


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Ankeny Regional Airport Yearly Rainfall (1951-2015)


Top Ten Daily Rainfalls in Ankeny Recorded Between Jan. 1951 – Dec. 2015

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Des Moines, Iowa, which is also located in Polk County near the watersheds, averages approximately 105 days of measurable rainfall per year (defined as at least 0.01 inches). Most rainfall events are small, as demonstrated by information presented in the Iowa Stormwater Management Manual, Section 2C-2, Table 1 (IDNR, 2009). The data shows that 90.60% of the measurable rainfall events were 1.25 inches or less. On average, Des Moines has 20 days per year in which rainfall exceeds 0.5 inches and 7 days per year in which rainfall exceeds 1 inch. However, large localized rainfall events do occur, on occasion, and amounts in excess of 12 inches per day have been recorded. Table 2-3 includes a few of Iowa’s largest daily rainfall events.

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Streamflow Gage Data

No streamflow data for Mud, Camp, and Spring Creeks are available via United States Geological Survey (USGS) gages. There is an Iowa Flood Center bridge sensor on each of the creeks to monitor water levels for flooding concerns. Their locations are listed below and also shown in Figure 2-25.

  • Mud Creek: Highway 163/NE 12th Ave in Pleasant Hill
  • Camp Creek: Highway 163/NE 12th Ave in Mitchellville
  • Spring Creek: SE 32nd Ave in Pleasant Hill

Designated Use Classifications

Listed below are the definitions for the surface water classifications of designated use segments, according to Iowa Administrative Code 567, Chapter 61. The designated uses of each creek are as follows: Mud Creek – Classes A2 and B(WW-2); Camp Creek – Classes A2, A3, and B(WW-2); and Spring Creek – Classes A1 and B(WW-2).

  • Primary contact recreational use (Class “A1”): Waters in which recreational or other uses may result in prolonged and direct contact with the water, involving considerable risk of ingesting water in quantities sufficient to pose a health hazard, including swimming, diving, water skiing, and water contact recreational canoeing.
  • Secondary contact recreational use (Class “A2”): Waters in which recreational or other uses may result in contact with the water that is either incidental or accidental, including fishing, commercial and recreational boating.
  • Children’s recreational use (Class “A3”): Waters in which recreational uses by children are common, which would primarily occur in urban or residential areas.
  • Cold water aquatic life – Type 1 (Class “B(CW1)”): Waters in which the temperature and flow are suitable for the maintenance of a variety of cold water species.
  • Cold water aquatic life – Type 2 (Class “B(CW2)”): Waters that include small, channeled streams, headwaters, and spring runs that possess natural cold water attributes of temperature and flow.
  • Warm water – Type 1 (Class “B(WW-1)”): Waters in which temperature, flow and other habitat characteristics are suitable to maintain warm water game fish populations along with a resident aquatic community that includes a variety of native nongame fish and invertebrate species.
  • Warm water – Type 2 (Class “B(WW-2)”): Waters in which flow or other physical characteristics are capable of supporting a resident aquatic community that includes a variety of native nongame fish and invertebrate species.
  • Warm water – Type 3 (Class “B(WW-3)”): Waters in which flow persists during periods when antecedent soil moisture and groundwater discharge levels are adequate; however, aquatic habitat typically consists of nonflowing pools during dry periods of the year.
  • Lakes and wetlands (Class “B(LW)”): Waters that are artificial and natural impoundments with hydraulic retention times and other physical and have chemical characteristics suitable to maintain a balanced community normally associated with lake-like conditions.
  • Human health (Class “HH”): Waters in which fish are routinely harvested for human consumption or waters both designated as a drinking water supply and in which fish are routinely harvested for human consumption.
  • Drinking water supply (Class “C”): Waters which are used as a raw water source of potable water supply.
The Mud, Camp, and Spring Creek Watersheds encompass approximately 101 square miles