Presentation on theme: "Introduction to Hydrology: Floodplains & Drainage Basins Lessons 21 & 22 Introduction to hydrology Introduction to hydrology Stream types, orders,"— Presentation transcript:
Introduction to Hydrology: Floodplains & Drainage Basins Lessons 21 & 22 Introduction to hydrology Introduction to hydrology Stream types, orders, and gradient Floodplains and landforms
Stream Systems Streams are bodies of water that are confined to a small region such as within stream banks Streams produce erosion, known as fluvial erosion Streams are also important for groundwater recharge and wildlife A stream may also be called a branch, brook, creek, crick, lick, bayou, wash, run, etc.
Stream Systems, cont. Usually, a stream begins at a location known as the headwaters This source location can be a spring or seep or a low area in a valley where water drains to Recall, water flows from high to low elevation Small streams flow downhill and converge into larger streams The point at which two streams merge is called the confluence The opposite of confluence is bifurcation, where one stream splits into two separate streams
Stream Systems, cont. As streams converge and diverge, they create a hierarchy of streams with different gradients, lengths, drainage areas, and total volume of water
Types of Streams Perennial streams are those that have flowing water 90% of the year in a well-defined channel Intermittent streams are those that have flowing water only during the wet season ( ≤ 50% of the year) Ephemeral streams generally have flowing water only after heavy rainfall events (e.g. thunderstorms) Winterbourne streams flow only during the winter months
Stream Characteristics Streams located on gentle slopes with low water velocities will flow back and forth, finding the lowest elevation to flow to This shift in the streams course is known as meandering Over time, a stream will meander back and forth across the flat valley floor, known as a floodplain Lateral erosion, shifts the course of the stream over time
Stream Characteristics, cont. This lateral erosion is concentrated along the outside bank of the meandering stream Primarily due to higher water velocity However, on the inner bank (slower moving water), soil and silt is being deposited Known as fluvial deposition Over time, lateral erosion and fluvial deposition gradually shift the course of the stream back and forth across the floodplain This results in the newer stream course being steeper, generally in a more straight direction with a faster flow
Stream Characteristics, cont. Erosion along the outer bank eats away at the soil (1) Further erosion forms a cut-off meander and a new stream/river channel (2) Eventually an ox-bow lake is created that is separate from the stream/river (3)
Stream Characteristics, cont.
Fast current = erosion
Stream Characteristics, cont. Slow current = deposition
Stream Characteristics, cont. Oxbow lakes may eventually become swamps, known as oxbow swamps If precipitation is low, these swamps may dry up and form small streams or dry stream beds known as meander scars
Floodplain Landforms Several types of landforms are associated with larger streams and rivers and the floodplains they produce
Floodplain Landforms, cont. Hills or ridges along each side of a major stream or river are known as bluffs If river flooding occurs, it generally does not reach this level Undercut banks or natural levees are formed from silt/soil deposits along the outer edge of the stream/river
Floodplain Landforms, cont. Streams that flow parallel to the main stream or river are called yazoo streams Yazoo streams are cutoff from the main stream due to natural levees When a stream/river meanders and cuts into itself it is called a cutoff meander This allows for the stream/river to take a shorter course
Floodplain Landforms, cont. A cutoff meander will initially become an isolated lake known as an oxbow lake When cutoff meanders fill with sediment and dry up, the become what’s known as meander scars
Floodplain Landforms, cont. As a stream/river cuts across the narrow neck of a meander (a), the cutoff river bend becomes an oxbow lake (b), which over time becomes an oxbow swamp (c), which in turn becomes a meander scar (d). From McKnight and Hess.
Drainage Basins A drainage basin or watershed is an area within which all water flows toward a single stream Watersheds are separated by what’s known as a drainage divide This is usually a ridge or some sort of man-made divide
Stream Orders Looking at an entire watershed we can see many streams which have various lengths, sizes, and patterns These streams can be analyzed through stream ordering A 1 st order stream is the smallest stream in a watershed or system of streams They do not have tributaries flowing into them Where two 1 st order streams meet, a 2 nd order stream is formed Where two 2 nd order streams meet, a 3 rd order stream is created However; when a 1 st order and 2 nd order stream meet, a 3 rd order stream isn’t formed Two 2 nd order streams are required to form a 3 rd order stream, etc, etc.
Stream Orders, cont.
Notice that the elevation gradient changes much faster between 1 st and 2 nd order streams than it does between 3 rd and 4 th order streams downstream
Quick Review Homework problems ask that you evaluate several topographic profiles. I highly suggest you refresh your memory and revisit lessons 5 and 6, which can be found online at: 2012/lectures/GEOG101L_Lessons_5-6.pptx
Quick Review, cont. Furthermore, recall that contour lines in the shape of a “V” indicate a stream or creek…with the apex of the “V” pointing uphill There are 63,360 inches in one mile There are 5,280 feet in one mile Page 139: Problem 2a-2d, bonus worth 1pt. If you need help at all, please me to setup an appointment or come see me during office hours…
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