Geography 102 week 9 notes
Geography 102 week 9 notes GY 102
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This 5 page Class Notes was uploaded by Elle Notetaker on Friday October 14, 2016. The Class Notes belongs to GY 102 at University of Alabama - Tuscaloosa taught by Lisa Davis in Fall 2016. Since its upload, it has received 5 views. For similar materials see Earth Surface Processes in Geography at University of Alabama - Tuscaloosa.
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Date Created: 10/14/16
GY 102 week 8 10/11/16 Components of the hydrologic cycle include surface and subsurface processes including infiltration, runoff, and related factors; watershed, and how spatial scale and drainage divides determine watershed boundaries. River basics. a. definition: Fluvial water- actively flowing, channelized water. It can connect to lakes. Water quantity and Tectonic processes can change long-term- they change elevations. Human activities can also cause fluctuations in rivers- compacting ground, removing vegetation, etc. change the amount of sediment, timing of water deliveries and the amount of sediment in the river. Rivers… i. Transport water, ii. sediment (from hills, river bank) also stores sediment in flood banks, iii. shape the landscape- valleys, floodplain. II. Basic components of River Systems a. Watershed- rivers in the US are managed based on watersheds, or the area that catches precipitation and drains it to a river. What happens to the land happens to the river. Drainage divides are topographic barriers that separate water going to different rivers. Stream water flows across the ground to find a river- this is runoff and is important. The dendritic water pattern, in which the water flow looks like a tree, is very common in wet climates. Drainage patterns develop according to geography. Drainage divides can be hills or mountains, and water follows the slope. Watersheds are scalable- you can look at the water that goes into just a stream or the entire river. th MARS: Mobile-Alabama River Systhm is the 4 biggest watershed in the US by flow volume and the 6 biggest river system in the US b. Channel- where the water’s flowing. Characterized by size & shape. Width & avg. depth are measured to determine how much water the channel holds. i. Shape- helps to determine the discharge (the amount and rate of flow at a place ex. 550 ft^3/s). Also the sediment load is measured, which affects the shape. Gradient, or longitudinal profile, is the elevation of the channel bed. ii. Watershed management and characterizing discharge. rate and volume of water moving past a point are measured in ft^3/s or cm^3/s. Continuity equation: Q=WDV. Q is discharge. Width, depth, velocity. WD grouped as A(cross sectional area) to make q=av. Stage is the height of the water above the channel bed. As flow goes up, so does the stage. Bank-full stage is when the stage is the highest it can get before the channel floods. iii. Rating curve- relates stage water to discharge. Lets you estimate the discharge using past records. If the water is at a height that hasn’t been measured before, you can estimate the discharge using the curve. Flood prediction involves predicting the timing and amount of discharge and the frequency based on probability theory. Frequency of flooding in the past can indicate the amount of flooding in the future. Flood recurrence interval is the chance a flood of particular size will occur in a given year; also expresses the avg frequency of flood of a certain size. Use the flood history to predict it. Uses the history of discharge change at one location/cross section and is based on the rating curve there (10 yr min for rating curve). Ri(recurrence interval)=(N+1)/R n=# years of discharge data, r = Rank of flood size. 100 yr flood, 50 yr flood, etc. 100yr flood- this place floods on avg every 100 years. Could be 10ft^3/s or 50,000ft^3/s. recurrence interval doesn’t indicate size of flood, just the frequency. 100yr flood = 1% flood: risk is the same every year even if it happened last year. There’s a relationship between the frequency and magnitude of floods. Greater frequency = smaller magnitude. Less frequent= larger magnitude. Randomness is a problem- probability doesn’t deal with the change. Flood prediction: probabilities. Probability (any given year)=1/Ri Randomness creates error in flood prediction. There’s virtually no data on extreme floods- equipment is wiped out. This can cause issues like 500/100 yr flood happening in the same place in successive years. Extreme events are poorly represented in stage/discharge and meteorological records. Oldest records are probably 50 yrs in most places. Management issues: FEMA uses the recurrence issues, which is why we use RI. Create floodplain maps and make people buy flood insurance. 10/13/16 thurs. Gy1012 Storm Hydrographs are used when flooding is imminent. Meteorologists predict how much water will be produced, hydrologists find out what will happen to the flow- where will it go, how fast, where will the discharge rise, and how fast? Hydrographs show the change in discharge/stage over x time. Hydrographs can be for various time periods. Parts of a hydrograph: -rising limb (when discharge increases due to increased runoff. Precipitation has been happening) -falling limb (discharge begins to decrease because precipitation has stopped.) -Lag time (time between the precipitation beginning and the peak, or highest, discharge. Lag time varies a lot.) Climate can affect when an area has peak discharge seasonally. a) Shape of hydrograph is determined by a. Storm characteristics, including intensity and duration. If there is high intensity, the runoff will increase quickly, as will discharge. With high duration events, it can be a slow, steady rise in discharge with high lag time. b. Watershed characteristics, including the size, shape, and land use. The time it takes for water to move to the river is important, as is the distance the water has to move. If the watershed is elongated, water has to move farther than if the watershed is compact- topography plays a big role. Infiltration and impervious surfaces are very important. Impervious surfaces can increase flood risk- every developed country has this as an issue. The runoff happens faster and in larger amounts. Groundwater Groundwater is water in the subsurface. Most places can store at least some water for some time. A. Zones of water a. Surface-infiltration b. Unsaturated zone-soil moisture. There is water, but not all the pore space is filled. c. Saturated zone-groundwater/water table- between the soil layers, it can be in rock bodies, limestone, and other carbonate rocks (carbonate rocks are prone to dissolution, which creates cavities for water to stay in. The water table is the boundary between the saturated and unsaturated zones. Water table is not always totally flat; it can change based on soil characteristics and saturation. B. Aquifer Systems- Saturated Zones. a. Aquifer: a rock body that can hold or transport water and is permeable; there are different types. Unconfined Aquifer is exposed to the surface by sediment. They replenish easily. The water going into an aquifer is recharge. Confined Aquifers or artesian wells/aquifers have an impermeable layer above (sometimes below as well) where water can’t get through. Mineral clay often forms an impermeable layer. Confined aquifers are less prone to contamination, but the recharge zone is limited and smaller than an unconfined aquifer. The Ugalala aquifer was once one of the biggest aquifers in the US, and was one of the largest naturally occurring aquifers, created by melting glaciers. C. Surface Water and Groundwater Connections a. Gaining streams, like the Black Warrior and Cahaba rivers get some flow from groundwater. Baseflow is what comes from groundwater. Frequent in temperate or warm, wet climates. b. Losing streams provide water to the groundwater system. These are more typical in arid and semi arid climates and frequently don’t have much water/flow. D. Groundwater Quantity Issues a. Reduction in recharge- climates growing dryer or people start taking out more water b. Accelerated withdrawal- if people take more than goes in c. Aquifer mining d. Exhaustion of fossil water- it can’t be replaced under current climate conditions. Water you use is used. Ex: ogalala aquifer. e. Decrease in GW quantity causes: drawdown- use lowers the water table, which increases the price to get the water. Cone of depression- over time, the water table in that area lowers and you have to relocate the well. The cone of depression also causes surface subsidence, making the ground surface sink in on itself. The space that had been occupied by water is no longer there. E. Quality issues a. Contamination- chemical spills or radioactive materials that come in contact with water are divided into point and nonpoint sources. i. Point sources are where the origin point is easily identified- if there is cadmium (unusual in nature, but a major battery ingredient) in water, it might be traced to a battery factory. These are fairly easily dealt with. ii. Non-Point sources have many potential sources. Ex. E. coli can get in through birds hanging out in a lake, people not picking up after pets, or farms. Nutrients (primarily Nitrogen and Phosphorus) are 2 of the 3 major pollutants of the U.S.’s rivers, used as fertilizers for agriculture and cause algae blooms and dead zones. Sediments ruin habitats for some organisms. They run into rivers. *On the test: The opposite of an aquifer is an Aquaclude- a rock body that won’t hold water because it has low permeability. Discharge: Q=AV. Calculate Q, calculate & interpret flood recurrence interval, read & interpret parts of a storm hydrograph, determine the shape of a hydrograph.
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