Chapter 9

1. Chapter 9 Surface Water

2. Chapter - 9 • Section – 9.1 Surface Water Movement (Water Cycle) • Section – 9.1 Stream Development • Section – 9.1 Lakes & Freshwater Wetlands

3. SECTION 9.1Surface Water Movement Objectives Describe how surface water can move surface materials. Explain how a stream carries its load. Describe how a floodplain develops.

4. Section 8.1 Running water is an agent of erosion, carrying sediments in streams and rivers and depositing them downstream. Review Vocabulary solution: A homogeneous mixture in which the component particles can not be distinguished.

5. New Vocabulary • runoff • watershed • divide • suspension • bed load • Discharge • Flood • floodplain

6. The Hydrologic Cycle The water cycle also referred to as the hydrologic cycle, is a never – ending, natural circulation of water through Earth’s systems.

7. Runoff • Water flowing downslope along Earth’s surface is called runoff. Runoff might reach a stream, river, or lake. It might evaporate, or accumulate as puddles in small depressions and infiltrate the ground. • Factors that determine how much precipitation becomes runoff • Soil composition • Rate of precipitation • Vegetation • Slope

8. Runoff: Soil Composition • If the porosity of a soil is greater, then more precipitation will soak into the ground instead of becoming runoff. • Coarse grained soils (sands and gravels) have high porosity - allowing more water to soak in. • Fine grained soils (silt and clay) have low porosity and cause more water to become runoff.

9. Runoff: Rate of Precipitation • There is a limit to how fast water can soak into the ground – called the rate of infiltration. • If precipitation falls at a faster rate than it can soak into the ground, it will generate more runoff.

10. Runoff: Vegetation & Slope • Vegetation will slow down the rate of runoff. • Water flowing through grass will move at a slower rate than water flowing across a parking lot. • If the slope is steeper, then the runoff will be faster.

11. Streams • Runoff generally begins as water flowing across the ground in thin sheets. • Eventually it finds its way to a channel • Channel can be a rill, gully, curbside gutter, or other low spot • Water flowing in a channel is a stream. • Streams organize themselves into systems

12. Stream Systems • A stream system is a network of streams that takes water out of an area. • Streams usually begin small and gradually merge with other streams as they flow down hill. • A stream that flows into another stream is called a tributary. • The further downhill a stream goes, the more tributaries it collects and the larger it gets. • Eventually the stream ends when it empties into a large lake or the ocean.

13. Stream Systems • Watershed – The land area drained by a stream system • Divide – The high land area that separates one watershed from another • Streams start - headwaters • Discharge point - mouth

14. Watersheds • Your local watershed is the Blackstone River • There are also “sub watersheds” in the Blackstone River Valley • West River • Mill River • Mumford River

15. Watersheds The watershed of the Mississippi River includes many stream systems. Approximately one third of the continental United States eventually drains into the Mississippi River.

16. Stream Load • Sediment carried by streams is called the stream load. • Stream load can be carried in one of 3 ways: • Suspension – smaller particles “float” along because of turbulent water • Bed Load – heavier particles (sand, gravel, cobbles, boulders) that “roll” along the stream’s bed • Solution – materials with soluble minerals dissolved in the stream’s water

17. Stream Carrying Capacity • The ability to transport the sediments by stream depends on how fast it flows (velocity) and on the volume (discharge) of water flowing. • The slope, depth, and width of the channel of the stream affect the speed and direction of the water moves within it. • A stream’s water moves more quickly with less friction. • A smooth - sided channels with great slope and depth allow water to move most rapidly.

18. Stream Discharge • Discharge is the measure of volume of stream water that flows past a particular locationover a givenperiod of time • Discharge can be found by multiplying (depth) (width) (velocity) • Its units are gallons / minute cubic feet / second cubic meter / second

19. Floods • Floods occur when water levels in a stream rise and flow over the stream banks onto the adjacent land. • At this point the stream is in flood stage • Floodplains are broad, flat areas adjacent to stream channels that get submerged during flooding. • During a flood, water flowing over the floodplain flows slower than it would in the channel. This causes sediment to be deposited on the floodplain.

20. Floods • The sediments deposited on a floodplain are often very fertile – good crop land. • Over time a river that floods often will build up natural levees that help reduce the frequency of floods by raising the height of the river banks.

21. Floods • Areas prone to floods may have flood warning systems established. • Dams and artificial levees can also help control flooding. • This picture is when a hurricanecaused massive floods inarea during 1955. • Floods like this promptedthe construction of WestHill Dam.

22. Flood Monitoring and Warning Systems • Government agencies like National Weather Service and Earth – orbiting weather satellites collect and transmit information about weather conditions, storms, and streams. • USGS has 7300 gaging stations in the United States to provide a continuous record of the water level in each stream. • In areas that are prone to severe flooding, warning systems are the first step in implementing emergency management plan.

23. SUMMARY • Running water is an agent of erosion, carrying sediments in streams and rivers and depositing them downstream. • Infiltration of water into the ground depends on the number of open pores. • All the land area that drains into a stream system is the system’s watershed. • Elevated land areas called divides separate one watershed from another. • A stream’s load is the materials that it carries. • Flooding occurs in small, localized areas as upstream floods or in large downstream floods.