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Weathering Leads to sediment source Rocks must be broken down into smaller components Sediment generated from rocks termed clastic sediment Clastic refers to fragments of rocks Sediment generated transported to oceans Coarser sediment forms beaches or other depostional features Deltas Or transported to deep ocean Fine grained sediment transported to shelf, slope, deep ocean Weathering •Weathering: the disintegration, or breakdown of rock material 2 Types of Weathering Mechanical Weathering: no change in chemical composition--just disintegration into smaller pieces Chemical Weathering: breakdown as a result of chemical reactions Mechanical Weathering Physical breakup • pressure release • water: freeze - thaw cycles • crystallization of salt in cracks • thermal expansion and contraction All this increases the total surface area exposed to weathering processes. Mechanical Weathering Exfoliation: Rock breaks apart in layers that are parallel to the earth's surface; as rock is uncovered, it expands (due to the lower confining pressure) resulting in exfoliation. Weathering Mechanical Weathering Sheet Joints (Exfoliation) Stone Mountain, GA Half Dome, Yosemite, CA Exfoliated Domes, Yosemite Stone Mountain, Georgia, showing the product of exfoliation due to unloading Stone Mountain, GA Frost Wedging: rock breakdown caused by expansion of ice in cracks and joints Shattered rocks are common in cold and alpine environments where repeated freeze-thaw cycles gradually pry rocks apart. Weathering Thermal expansion due to the extreme range of temperatures can shatter rocks in desert environments. Repeated swelling and shrinking of minerals with different expansion rates will also shatter rocks. Role of Physical Weathering 1) Reduces rock material to smaller fragments that are easier to transport 2) Increases the exposed surface area of rock, making it more vulnerable to further physical and chemical weathering Chemical Weathering Definition: transformation/decomposition of one mineral into another Mineral breakdown • carbonate dissolves • primary minerals --> secondary (mostly clays) minerals Net loss of elements retained in the soil. Dissolution H2O + CO2 + CaCO3 --> Ca+2 + 2HCO3- water + carbon dioxide + calcite dissolve into calcium ion and bicarbonate ion Biological activity in soils generates substantial CO2 Bicarbonate is the dominant ion in surface runoff. Erosion Sediments produced by weathering are then removed by erosion Erosion - the incorporation and transportation of weathering products by a mobile agent such as wind, water, ice. Rivers Introduction • Rivers and streams are dynamic systems that continually adjust to natural and human-caused changes • Running water is the most important geologic agent modifying Earth’s land surface and is a source of fresh water for industry, agriculture, and domestic use • Management of erosion and flooding requires considerable effort and cost http://www.co.monterey.ca.us/OES/floods_files/Salinas_River_Floods.jpg Salinas River, CA Hydrologic Cycle • Water is cycled from oceans, through atmosphere, to continents, and back to the oceans • Powered by solar radiation and occurs because water changes readily from liquid to a gas on surface Evaporation, condensation, precipitation, and runoff characterize the movement of water, though some is stored in lakes, groundwater, and ice Moving Water Sheet flow Sheet Flow water moves in a continuous sheet of shallow watermoving over the surface www.duluthstreams.org/.../ impact_impervious.html Channel Flow water is confined to long trough-like depressions LA River Channel http://upload.wikimedia.org/wikipedia/commons/0/07/Los_Angeles_River_Glendale.jpg A Drainage Basin A drainage basin is extent of land where water from rain and melting snow or ice drains downhill into a body of water, such as a river, lake, reservoir, estuary, wetland, sea or ocean. The drainage basin includes both the streams and rivers that convey the water as well as the land surfaces from which water drains into those channels Drainage BasinsSouthern California http://www.urbanedpartnership.org/target/units/river/drainage_map.gif OC Public Works Important River Parameters Gradient, Velocity, and Discharge Gradient is the average slope of the channel bed Velocity is the distance water travels in a given amount of time Discharge is the volume of water passing a point in a given amount of time Ability to transport sediment depends on velocity which also depends on gradient River Sediment Transport Sediment transported as: Bedload Suspended loads such as clays Saltation, traction, rolling of grains—e.g. sand, pebbles, boulders Most comes from slopes Most comes from soils Solution load from dissolved minerals Deposition by Running Water Braided Streams network of connecting dividing channels, separated by sand and gravel bars develop when sediment supply exceeds transport capacity of running water Deposition by Running Water Meandering Streams defined by a single channel with broadly looping curves cutbanks are found on the outside of meanders, point bars on the inside unequal flow velocities in channels accounts for deposition and erosion in predictable patterns Incised Meanders Develop where an older meandering pattern is cut into underlying bedrock as tectonics uplift the region Channel Width and Depth Width mostly controlled by silt & clay in banks More cl & slt = wider channel The wider the channel the shallower the depth. The Significance of Base Level Base level is the lowest level to which any stream can erode River cannot cut below its mouth Sea level is taken to be the ultimate base level, but the rising of the sea or subsidence of land over geologic time make this concept a relative one Local base levels may control erosion and deposition Graded Streams Graded streams develop over time as a balance between gradient, discharge, flow velocity, channel shape, and sediment load is reached • The concept is an ideal, but gives us a model to understand responses to changes in these parameters Think about dams on our LA, San Gabriel and Santa Ana Rivers Predictions of Adjustment to Base Level Changes Malibu, Bolsa Chica, Bolinas Describe how these creeks would change and the impacts that these changes will have on the sediment supply to beaches and other regions of the coast if : Sea Level Dropped due to global cooling Tectonic uplift of coastal area Sea Level drops and tectonic uplift of coast occurred together Sea Level rises due to global warming Tectonic down dropping of coast A dam is placed on the mid-point of the creeks A resistant outcrop occurs in the mid-point of the creek Excavation of the creek bottom in the mid-point of the creek occurs because of gold mining Deltas Flow velocity decreases as water flows into lakes or oceans deposition occurs and may lead to the origin of a delta, which can prograde as sediment is continually supplied by the stream topset, foreset, and bottomset beds Sacramento River Delta NASA Ganges River Nile River Mississippi Delta Santa Clara River Nasa Malibu Creek www.santamonicabay.org/.../ tabid/77/Default.aspx LA River scmi.us/.../ ci-core/la-river San Gabriel River Nasa Meandering Streams Oxbow lakes form when meanders become so sinuous that the thin neck of land between them is cutoff during floods How Do Valleys Form and Evolve? Valleys usually have rivers running their length, with tributaries draining highlands on either side downcutting occurs when a stream has excess energy to deepen its course Flooding Rating Floodplain Risk Streamflow Measurement Most common practices are dams and levees both require large capital investments and constant maintenance they are constructed to control finite amounts of water and sediment; if that is exceeded the water will end up in the floodplain anyway Estuaries Where the Rivers meet the Sea Semi- enclosed body of water where there is a mix of river and seawater, and mix of fluvial and marine processes Mouths of many rivers flooded at last sea level high (last interglacial) Boundary between fluvial and marine processes Influenced by tides Tectonic San Francisco Bay Fjord Chesapeake Bay: Drowned Shoreline ESTUARY The Netherlands Barrier Island Wetlands – lands covered with water all or part of a year Wetlands purify water, act as flood control, & help stabilize shoreline. Are biologically diverse Wetland Conditions Hydric (saturated) soils – formed under conditions of saturation, flooding, or ponding long enough during growing season to produce anaerobic conditions in upper Hydrophytic plants – adapted to thrive in wetlands despite the stresses of an anaerobic and flooded environment Hydrologic regime – dynamic or dominant presence of water Wetland Classification Chart Major Categories General Location Wetland types Marine (undiluted salt water) Open coast Shrub wetland, salt marsh, mangrove swamp Estuarine (salt/freshwater mix) Estuaries (deltas, lagoons) Brackish marsh, shrub wetland, salt marsh, mangrove swamp Riverine (associated w/ rivers and streams) River channels and floodplains Bottomlands, freshwater marsh, delta marsh Lacustrine (associated w/ lakes) Lakes and deltas Freshwater marsh, shrub and forest wetlands Coastal Wetlands: Inland Wetlands: Palustrine (shallow ponds, Ponds, peatlands, misc. freshwater wetlands) uplands, ground water seeps Ephemeral ponds, tundra peatland, ground water spring oasis, bogs Physical/Hydrological Functions of Wetlands Flood Control Correlation between wetland loss and downstream flooding can capture, store, and slowly release water over a period of time Coastal Protection Serve as storm buffers Ground Water Recharge Water has more time to percolate through the soil Sediment Traps Wetland plants help to remove sediment from flowing water Atmospheric Equilibrium Can act as ‘sinks’ for excess carbon and sulfur Can return N back to the atmosphere (denitrification) Chemical Functions of Wetlands Pollution Interception Nutrient uptake by plants Settle in anaerobic soil and become reduced Processed by bacterial action Toxic Residue Processing Buried and neutralized in soils, taken up by plants, reduced through ion exchange Large-scale / long-term additions can exceed a wetland’s capacity Some chemicals can become more dangerous in wetlands (Mercury) Value of Estuaries Greatly influenced by river discharge and tidal mixing. Environmental conditions fluctuate widely. Biomass is high because estuaries have high nutrient levels. Species diversity is low because fewer species can cope with the wide fluctuations in temperature, salinity etc. “nursery grounds” young stages develop in the estuary (abundant food; low predation may move offshore to adult habitats Riparian System What is a Riparian Area? Riparian zones or areas have been defined in several ways, but they are essentially the narrow strips of land that border creeks, rivers or other bodies of water. Because of their proximity to water, plant species and topography of riparian zones differ considerably from those of adjacent uplands. Although riparian areas may occupy only a small percentage of the area of a watershed, they represent an extremely important component of the overall landscape. This is especially true for arid-land watersheds, such as those in Eastern Oregon. Functions of a Healthy Riparian System: 1. Sediment Filtering 2. Bank Stablilization 3. Water Storage and Release 4. Aquifer Recharge 5. Wildlife Habitat Riparian System A healthy system would have some or all these characteristics: 1.) High water table & increased storage capacity, 2.) High forage production, 3.) Good shade-Cool water, 4.) Good fish habitat-Good water quality, 5.) High wildlife habitat diversity, 6.) Vegetation & roots present to protect & stabilize banks, 7.) Higher late summer stream flows. •Denton Creek