GEOL 108Lg 1st Edition Lecture 14Outline of Last Lecture- Hurricanesa. Mass wasting phenomena, causes- WavesOutline of Current Lecture- Hydrologic Cycle, Concept of Residence Time- Climate and Rain- Dams and Rivers/Water UsageCurrent LectureW ater a n d Ene r gyGeology meets PoliticsWhat resources are essential for life (think agriculture), are in short supply and are most likely to lead to conflict among nations (or states)?1. Water2. EnergyThese are often intertwined, as water can be a source of energy and energy development often requires waterHyrdologic CycleWhere does water come from?Rain comes from clouds, clouds get water vapor from atmosphere, which comes from the ocean.Concept of Residence TimeIf a dynamic system is gaining and losing material at equal rates, the mass of the system is in steady state (this means that it does NOT change over time)dM/dt=Input - output=0the rate of input in steady state=the rate of outputresidence time= (system mass)/(input or output)Where does water sit?-Reservoirs of water-Most of the water we have (97%) is in the ocean-The rest of it mostly is in the polar ice caps-(the rest, groundwater, rivers/lakes/atmosphere)Note that the atmosphere can accumulate water quickly to produce a new storm, and also that groundwater has a long residence time and is not quickly replacedThinking about residence time, we can say ‘alright, how long does water stay in the ocean?’1 meter evaporated per year from oceanAverage water molecule spends about 4,000 years in the oceanVapor Pressure of WaterTo create rain, we need to move air into a saturated regionTHis requires cooling, or mixing 2 air masses (A+B) with different T Warm Air Mass + Cool Air Mass = RAINThe air is THINNER in the mountains, meaning that the atmospheric pressure issmaller at higher altitudes which allows the air to expandWhy does it rain?1. Two air masses near saturation, but with different temperatures, are mixed. 2. Air rises, causing it to coolClimate BandsLower and Higher Latitudes experience different climates, obviously. Hottest air rising at the ITZ.Rai n fa l l P at t e r n in c ali f o rn iaSources of Water in So CAlOrographic Rainfall:Los Angeles served by the Los Angeles Aqueduct and the Colorado River & State WaterProject (taking water from sierras, sending it to LA)Process that uses 10x more water than municipal uses? AgricultureDams:Cost benefit AnalysisBe n efi t s1. Flood Control2. Hydroelectric power3. Water storage for dry timesCo s ts1. Loss of water through evaporation and infiltration2. Loss of land and some recreational opportunities3. Seismicity4. Downstream impacts: less water, salinization, erosion5. Siltation in reservoirs6. Barrier to fish migration for spawningVelocity Profiles in StreamStrem Cross Section of Channel-Braided Rivers (look up a photo on google)-Madison River Terraces (“”)-Mosaic Canyon (“”) - note old terracesT e rr a c esBedforms and Flow VelocityBedforms develop in response to flow, types depend on velocity (can be used to deduce past high velocities). Ripple spacing also depends on v (water