Section 1 The Active River

The Water Cycle Is the continuous movement of water Water moves from the ocean to atmosphere to land Is driven by the sun’s energy

River Systems Network of streams and rivers that join together Tributary – a stream that flows into a lake or larger stream Example: Rocky River is a tributary of the Yadkin-Pee Dee River Divided into regions called watersheds (aka: drainage basin or river basin) River systems help drain watersheds

Watersheds Area of land drained by a water system Land surrounding a water system Largest watershed in U.S. is the Mississippi River watershed Other major watersheds Columbia River Rio Grande Colorado

NC Watershed Map

Divide Separates watersheds Area of higher ground In U.S., Continental Divide runs through Rocky Mountains and separates watersheds that flow into the Atlantic from those that flow into the Pacific

Stream Erosion As a stream forms, it erodes soil and rock to make a channel Channel is the path a stream follows When stream first forms, channel is narrow and steep Over time, channel gets wider and deeper Eventually a stream becomes a river Stream’s ability to erode is influenced by 3 factors Gradient Discharge Load

Gradient Is the measure of change in elevation over a certain distance High gradient = more erosive energy Low gradient = less energy for erosion

Discharge Is the amount of water a stream or river carries in a given time Discharge increases Storm occurs (lots of rain) Rapid snow melt As discharge increases, erosive energy, speed, and amount of materials the stream can carry increases

Load Materials carried by a stream Size of load is affected by stream’s speed (Fast can carry larger particles) Three types of materials carried by a stream: Bed Load: large materials like pebbles and boulders Suspended Load: Small rocks and soil that float in water; makes water look muddy Dissolved Load: material carried in solution (dissolved in water); ex. – calcium and sodium

Stages of a River Youthful Channel is deeper instead of wider Narrow and Straight Steep Gradient Fast Flowing Rapids and Waterfalls Few Tributaries

Stages of a River Mature Channel is wider instead of deeper Gradient not as steep Fewer falls and rapids Many tributaries More discharge

Stages of a River Old Low gradient Little erosive energy Deposits rock and soil in channel Wide, flat floodplain Many bends (meanders) Fewer tributaries (because smaller tributaries have joined) Photo from textbook pg. 46

Stages of River Rejuvenated Found where land is raised by tectonic activity Increased gradient Faster flow Terraces - step like formations form on sides of river Photo from textbook pg. 46