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Geosciences LibreTexts

5: Water

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  • Learning Objectives

    After completing this chapter, you should be able to:

    • Understand how streams erode, transport, and deposit sediment
    • Know the different stream drainage patterns and understand what they indicate about the underlying rock
    • Explain the changes that happen from the head to the mouth of a stream
    • Understand the human hazards associated with floods
    • Know the properties of groundwater and aquifers
    • Understand the distribution of groundwater, including the water table
    • Learn the main features associated with karst topography
    • Understand the challenges posed by karst topography

    • 5.1: Introduction
      Think how many times a day you take water for granted – you assume the tap will be flowing when you turn on your faucet, you expect rainfall to water your lawn, and you may count on water for your recreation. Not only is water necessary for many of life’s functions but it is also a considerable geologic agent. Water can sculpt the landscape dramatically over time both by carving canyons as well as depositing thick layers of sediment.
    • 5.2: Streamflow and Parts of a Stream
      The running water in a stream will erode (wear away) and move material within its channel, including dissolved substances (materials taken into solution during chemical weathering). The solid sediments may range in size from tiny clay and silt particles too small for the naked eye to view up to sand and gravel-sized sediments. The smaller particles kept in suspension by the water’s flow are called suspended load. Larger particles typically travel as bedload, stumbling along the stream bed.
    • 5.3: Stream Gradient and the Cycle of Stream Erosion
      Stream gradient refers to the slope of the stream’s channel, or rise over run. It is the vertical drop of the stream over a horizontal distance. Stream gradients tend to be higher in a stream’s headwaters (where it originates) and lower at their mouth, where they discharge into another body of water (such as the ocean). Discharge measures streamflow at a given time and location and specifically is a measure of the volume of water passing a particular point in a given period of time.
    • 5.4: Lab Exercise (Part A)
      This page contains the lab exercise regarding the drainage patterns.
    • 5.5: Flooding
      Flooding is a common and serious problem in our nation’s waterways. Flood stage is reached when the water level in a stream overflows its banks. Floodplains are popular sites for development, with nice water views, but are best left for playgrounds, golf courses, and the like. Have you ever heard someone say that a flood was a 1-in-100-year flood? Does that mean that a flood of similar magnitude will occur every 100 years?
    • 5.6: Lab Exercise (Part B)
      Data from the chart below was collected at the USGS site and includes the 20 largest discharge events for Sweetwater Creek at station 02337000 from January 1, 2008 – May 1, 2015, excluding the dramatic 2009 flood (we will learn more about it later). In order to create a flood frequency graph, the recurrence interval must first be calculated. A recurrence interval refers to the average time period within which a given flood event will be equaled or exceeded once.
    • 5.7: Groundwater
      It is best not to envision groundwater as underground lakes and streams (which only occasionally exist in caves). Instead, think of groundwater slowly seeping from one minuscule pore in the rock to another. Have you ever been to the beach and dug a hole, only to have it filled with water from the base? If so, you had reached the water table, the boundary between the unsaturated and saturated zones.
    • 5.8: Lab Exercise (Part C)
      Many gas stations use underground storage tanks (UST) to store fuel below the ground (you have likely seen a tanker truck at a gas station filling up the UST). These UST’s could leak, and gasoline could possibly reach the water table. In the diagram below, a business using a well has detected gasoline in their groundwater. To detect the source of the potential leak, contour the water table’s surface and determine its flow path.
    • 5.9: Karst Topography
      The sedimentary rock limestone is composed of the mineral calcite, which is water-soluble, meaning it will dissolve in water that is weakly acidic. In humid areas where limestone is found, water dissolves away the rock, forming large cavities and depressions which vary in size and shape. As more dissolution occurs, the caves become unstable and collapse, creating sinkholes. These broad, crater-like depressions are typical of karst topography, named after the Karst region in Slovenia.
    • 5.10: Lab Exercise (Part D and E)
      Use the Mammoth Cave, Kentucky map (Map 5.4 located at the end of this chapter) to answer the following questions. Though it is old (1922), the general geology and landforms in this area have not changed.
    • 5.11: Student Responses
      The following is a summary of the questions in this lab for ease in submitting answers online.