quiz 1_ streams and river+calc.pdf

Quiz 1: Rivers and streams + calculations Objectives: 1. How are the boundaries of a watershed determined on a map? Identify them, too. 2. What are the factors that impact how a river transports water and sediment? 3. How do stream and river f...

Quiz 1: Rivers and streams + calculations Objectives: 1. How are the boundaries of a watershed determined on a map? Identify them, too. 2. What are the factors that impact how a river transports water and sediment? 3. How do stream and river features form? How do they change over time? 4. Using dimensional analysis, calculate discharge, area and velocity, and convert unites Basic: - River system: a river and all it’s tributaries - Tributaries: a stream/river that feeds into a larger stream/river How are the boundaries of a watershed determined on a map? - Watershed/drainage basin: a geographic area area where all the water—whether from rainfall, snowmelt, or streams—drains into a common outlet such as a river, lake, reservoir, or ocean.The boundaries are established by identifying the highest points of elevation, such as ridgelines, hills, mountains - Watersheds are natural boundaries that separate river systems - For example, water that falls on one side of a watershed divide might flow into the Mississippi River, while water on the other side could flow into the Colorado River - The high points (divides) create a natural boundary where water flows downhill into different directions, ultimately defining the area in which all precipitation drains into a common outlet, such as a river, lake, or ocean. 2. What are the factors that impact how a river transports water and sediment? - Stream gradient: steepness/slope of stream 1. High gradient → more kinetic energy → higher velocity: directly tied to stream competence and capacity 2. Weathering - Physical weathering (typically abrasion):  The breaking down of rocks into smaller pieces without changing their chemical composition High gradient sterams→ increased rate of physical abrasion - Chemical weathering: Alters the chemical composition of rocks (dissolving) Low gradient streams → increased rate of chemical weathering, because rocks have prolonged contact with water - Erosion - The process by which materials are worn away and transported by natural forces such as wind and water - Creates cut banks: steep eroded bank on outside of river meander because of the fast flowing water. The eroded material is carried down stream and deposited, creating point bars and possibly deltas Largely affected by stream gradient. In general, faster streams=more intense erosion. Faster moving streams erode vertically, low gradient streams erode laterally, making the river channel wider. Base level: the lowest point of erosion. As a river approaches base level, gradient decreases. Major in the creation of oxbow lakes: U shaped body of water formed when a meandering body of water creates a cutoff, and overtime the meander can be completely separate forming a lake. - Deposition Opposite of erosion (putting down and building up the sediment) Occurs when rivers and streams lose energy Typically occurs on the inside of the meander, where water moves slower, which can form point bars: a curved ridge of sand along the inner bank of a streams meander Influenced by grain size: largest particles are deposited first because they are too big to remain suspended Creates deltas. Velocity slows down a lot as rivers/streams feed into larger bodies. Larger materials deposited first, then smaller materials which creates the layered structure of deltas (very fertile land and great for farming)  Creates floodplains. When rivers overflow out of their banks, velocity slows down, meaning sediment is deposited. Larger particles are deposited closer to river banks, while smaller particles are deposited further. Repeated flooding builds thick layers of sediment and fertile floodplains. Creates natural levees (basically walls of sediment): raised banks of sediment formed along river channel as a result of multiple floods. Blocks water from going where we don’t want it to go. How do stream and river features form? And how they change over time Characteristics of youthful streams: - Steep, high gradient - Vertical erosion dominates over lateral erosion - Because of their powerful vertical erosion, they carve out steep and narrow V shaped valleys - The dominant vertical erosion is referred to as downcutting - Little → no meander because they are still downcutting. As streams age the erode more laterally and meanders begin to form. - Little to no floodplain, because their is barely any flat land surrounding youthful streams Characteristics of old age/mature streams: - Lateral erosion dominates over downcutting, creating wide meanders and low gradient streams - As old age streams meander, they create floodplains, or wide flat areas surrounding the streams - Focused on deposition rather than eroision Calculations Velocity: distance/time (typically m/s or ft/s) never cubed Discharge (Q): Q=A/V 1. Discharge is volume (whatever unit cubed) 2. Can be used to find velocity: Q/A = VxA/A (you must include this before simply writing velocity=Q/A) !!!! 3. Dimensional analysis