EARTH SCIENCE Geology, the Environment and the Universe Chapter 9: Surface Water

Surface Water Movement SECTION9.1 Surface Water Movement Running water is an agent of erosion, carrying sediments in streams and rivers and depositing them downstream.

Surface Water Movement SECTION9.1 Surface Water Movement New Vocabulary runoff watershed divide suspension bed load discharge flood floodplain

Surface Water Movement SECTION9.1 Surface Water Movement The Water Cycle The water cycle, also referred to as the hydrologic cycle, is a never-ending, natural circulation of water through Earth’s systems.

Surface Water Movement SECTION9.1 Surface Water Movement The Water Cycle

Surface Water Movement SECTION9.1 Surface Water Movement Runoff Water flowing downslope along Earth’s surface is called runoff.

Surface Water Movement SECTION9.1 Surface Water Movement Runoff Soil composition Soil that has open surface pores allows water to infiltrate. The particle size that makes up a soil helps determine the pore space of the soil. Large grain size Fine grain size Mixed grain size

Surface Water Movement SECTION9.1 Surface Water Movement Runoff Rate of precipitation If the rate of precipitation (e.g. rainfall) exceeds the rate of infiltration, the water will become runoff.

Surface Water Movement SECTION9.1 Surface Water Movement Runoff Vegetation Vegetation can slow the rate of runoff of surface water. Raindrops are slowed when they strike the leaves of trees or blades of grass, and they trickle down slowly.

Surface Water Movement SECTION9.1 Surface Water Movement Runoff Slope Water from precipitation falling on slopes flows to areas of lower elevation. The steeper the slope, the faster the water flows.

Surface Water Movement SECTION9.1 Surface Water Movement Stream Systems Tributaries Rivers that flow into other streams are called tributaries.

Surface Water Movement SECTION9.1 Surface Water Movement Stream Systems Watersheds and divides All of the land area whose water drains into a stream system is called the system’s watershed. A divide is an elevated land area that separates one watershed from another.

Surface Water Movement SECTION9.1 Surface Water Movement Stream Systems Watersheds and divides The watershed of the Mississippi River includes many stream systems, including the Mississippi, Missouri, and Ohio Rivers. The Continental Divide marks the western boundary of the watershed.

Stream Carrying Capacity SECTION9.1 Surface Water Movement Stream Carrying Capacity The ability of a stream to transport material, referred to as its carrying capacity, depends on both the velocity and the amount of water moving in the stream.

Stream Carrying Capacity SECTION9.1 Surface Water Movement Stream Carrying Capacity Discharge is the measure of the volume of stream water that flows past a particular location within a given period of time (measured in cu.ft./s or m3/s).

Stream Carrying Capacity SECTION9.1 Surface Water Movement Stream Carrying Capacity Stream discharge is the product of a stream’s average width, average depth, and the velocity of the water.

Surface Water Movement SECTION9.1 Surface Water Movement Floods A flood occurs when water spills over the sides of a stream’s banks onto the adjacent land.

Surface Water Movement SECTION9.1 Surface Water Movement Floods The broad, flat area that extends out from a stream’s bank and is covered by excess water during times of flooding is known as the stream’s floodplain.

Surface Water Movement SECTION9.1 Surface Water Movement Floods When rivers overflow their banks, the floodwater deposits sediment. Over time, sediment accumulates along the edges of a river, resulting in natural levees.

Flood Monitoring and Warning Systems SECTION9.1 Surface Water Movement Flood Monitoring and Warning Systems In areas that are prone to severe flooding, warning systems, such as those established by the National Weather Service and the U.S. Geological Survey, are the first step in implementing emergency management plans.

SECTION9.2 Stream Development Streams erode paths through sediment and rock, forming V-shaped stream valleys.

Stream Development New Vocabulary stream channel stream bank SECTION9.2 Stream Development New Vocabulary stream channel stream bank base level meander delta rejuvenation

Stream Development Supply of Water Stream channels SECTION9.2 Stream Development Supply of Water Stream channels The region where water first accumulates to supply a stream is called the headwaters.

Stream Development Supply of Water Stream channels SECTION9.2 Stream Development Supply of Water Stream channels The headward erosion of Stream A cuts into Stream B and draws away from its water into one stream, in a process called stream capture.

Formation of Stream Valleys SECTION9.2 Stream Development Formation of Stream Valleys The height of a stream above its base level determines how much downcutting energy the stream will have.

Formation of Stream Valleys SECTION9.2 Stream Development Formation of Stream Valleys Meanders A bend or curve in a stream channel caused by moving water is called a meander.

Formation of Stream Valleys SECTION9.2 Stream Development Formation of Stream Valleys Meanders Water moving along the outside of a meander curve has the greatest velocity erodes the side of the streambed. Along the inside of a meander, the water moves more slowly and deposition is dominant.

Formation of Stream Valleys SECTION9.2 Stream Development Formation of Stream Valleys Meanders

Formation of Stream Valleys SECTION9.2 Stream Development Formation of Stream Valleys Meanders A winding stream may cut off a meander and once again flow along a straighter path. The blocked-off meander becomes an oxbow lake, which eventually dries up.

Deposition of Sediment SECTION9.2 Stream Development Deposition of Sediment When streams lose velocity, they lose some of the energy needed to transport sediment, and deposition of sediment occurs.

Deposition of Sediment SECTION9.2 Stream Development Deposition of Sediment Alluvial fans Alluvial fans are fan-shaped, sloping depositional features that form when water flows down steep slopes onto flat plains.

Deposition of Sediment SECTION9.2 Stream Development Deposition of Sediment Deltas The triangular deposit that forms where a stream enters a large body of water is called a delta.

Stream Development Rejuvenation SECTION9.2 Stream Development Rejuvenation During rejuvenation, a stream resumes the process of downcutting toward its base level. This causes an increase in the stream’s velocity, and the stream’s channel once again cuts downward into the existing meanders.

SECTION9.2 Section Check How could a mature river near its base level be rejuvenated and start eroding downward again? Answer: A river can be rejuvenated when the land the river flows over is uplifted. A drop in sea level can also increase the vertical distance between the river channel and base level and cause the river to erode downward.

Lakes and Freshwater Wetlands SECTION9.3 Lakes and Freshwater Wetlands As the amount of water changes and the amount of sediments increases, lakes can be transformed into wetlands and eventually into dry land.

Lakes and Freshwater Wetlands SECTION9.3 Lakes and Freshwater Wetlands New Vocabulary lake eutrophication wetland

Lakes and Freshwater Wetlands SECTION9.3 Lakes and Freshwater Wetlands Origins of Lakes Natural lakes, bodies of water surrounded by land, form in different ways in surface depressions and in low areas.

Lakes and Freshwater Wetlands SECTION9.3 Lakes and Freshwater Wetlands Origins of Lakes Some lakes form when stream flow becomes blocked by sediment from landslides or other sources. Other lakes, such as moraine-dammed lakes, cirque lakes, and kettle lakes, have glacial origins.

Lakes and Freshwater Wetlands SECTION9.3 Lakes and Freshwater Wetlands Lakes Undergo Change A depression that receives more water than it loses to evaporation or use by humans will exist as a lake for a long period of time. However, over geologic time, most lakes are temporary features.

Lakes and Freshwater Wetlands SECTION9.3 Lakes and Freshwater Wetlands Lakes Undergo Change Eutrophication The process by which bodies of water become rich in nutrients that stimulate excessive plant growth is called eutrophication.

Lakes and Freshwater Wetlands SECTION9.3 Lakes and Freshwater Wetlands Lakes Undergo Change Eutrophication Although eutrophication is a natural process, it can be sped up with the addition of nutrients, such as fertilizers, that contain nitrogen and phosphorus.

Lakes and Freshwater Wetlands SECTION9.3 Lakes and Freshwater Wetlands Lakes Undergo Change A wetland is any land area that is covered with water for a part of the year.

Lakes and Freshwater Wetlands SECTION9.3 Lakes and Freshwater Wetlands Lakes Undergo Change Freshwater wetlands Wetlands play a valuable role in improving water quality.

Lakes and Freshwater Wetlands SECTION9.3 Lakes and Freshwater Wetlands The area of wetlands in the United States was drastically reduced until the 1980s. Since then, efforts have been made to preserve wetlands.

Surface Water How do wetlands improve water quality? CHAPTER9 Surface Water Chapter Assessment How do wetlands improve water quality? Answer: Wetlands trap sediment that might otherwise enter a stream or lake. Wetland plants reduce the concentration of nutrients in runoff. Some pollutants are trapped in wetland vegetation or by wetland sediment.