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UNC-Chapel Hill ENVR 104 - LECTURE NOTES

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ENVR 104Water Resource Management Module (Characklis)Lecture 1[REVIEW THESE NOTES WITH “ENVR 104 LECTURE 1 SLIDES.PDF”]COVER SLIDE- At its most basic, we are here to try to figure out how to effectively manage an increasinglyscarce water resource- Managing water resources has a number of technical challenges, but also has- Social- Economic- EnvironmentalAnd these can make it much more difficult to formulate management strategies- The objective of this module is to introduce students to basic methods of quantitativelyevaluating various management approaches, but also to make them aware of some of thebroader issues involved.- So, how do we manage our increasingly scarce water resources- I say increasingly, because there are many areas in the world where water isrelatively abundant.- However, the number of these places is declining. Why?- Because water is a finite resource, and this is particularly true for freshwaterSLIDE 2- What % age of world’s water is fresh? Not much ∼ 2.5%o Freshwater lakeso Riverso Groundwater (fresh) Remember that efficient pumps were not available prior to the1930s and 40s, so water supplies were mostly based on rivers andlakes up to that point Big impact on the way civilizations developed• Most cities that developed pre WWII did so on rivers/lakes• Only in the last 50-60 yrs did this begin to changeo Las Vegaso Los Angelesdimensions- So, water is everywhere, but only a relatively small fraction of it is usable without incurringsome considerable expense (i.e. desalination)- Nonetheless, we are still talking about 35⋅106 km3 of freshwater available globally- With 6⋅109 people in the world, this works out to about 0.006 km3/person ∼6,000,000 m3/person- Avg. person in developed world probably uses 0.3 – 0.5 m3/cap/day, 100-150m3/cap/yr (those in the developing world use much less)- Even if we assume 90% of this freshwater (or more) is totally inaccessible, it is still clear thatthere would be no scarcity if water were perfectly distributed (both temporally and spatially) tomeet human needsBut, that is clearly not the caseSLIDE 3(values are normalized such precipitation on land = 100)- We are largely dependent on the hydrologic cycle to determine when and wherewater is available.- In the end, it comes down to rainfall that runs off into rivers and lakes, orpercolates into aquifers.- Rainfall has cycles, both seasonal and climatic (drought), so in order to developthe reliable supplies that we need to keep society moving, we need to be able to“smooth out” our supply- We do this by storing excess water during periods of abundance and using thestored amount when water is scarce.o Nature does some of this for us ⇒ aquiferso We have learned to do this for ourselves ⇒ damsBut, there is a catchSLIDE 4- We have begun to exhaust the sustainable supply of groundwater, at least in theareas where it is most needed.o U.S. usage peaked in 70s-80s, and has hit a plateau. The rate of usage haseven declined slightly, suggesting that some aquifers have been pumped atlevels exceeding their recharge ratesSLIDE 5- A similar situation exists with respect to dams/reservoirs, as the United States hasdrastically slowed its development of these structures- 2 primary reasonso (1) Used up many of the most attractive sites deep, wide valleys, with narrow openings those that remain are increasingly expensive to developo (2) Growing awareness of the environmental impacts of dam building andincreasing public sentiment that these outweigh dam benefits inmany cases.- So, we are beginning to run up against limits in our ability to modify the temporal variations inwater availabilitySLIDE 6- But, we also have issues of spatial variability- Rain/snow does not fall equally in all places- Presumably, we could move water from where it is, to where it isn’t.- Nature does some of this for us by means of rivers (e.g., Colorado, Missouri,Snake, Columbia)- We also know how to do this ourselves,o pipelineo aqueducts- But, there are a couple problemso Expensive!! Water is heavy. Capital & O&M costs are high.o Environmental consequenceso Political implicationsSLIDE 7- Nonetheless, we have installed large conveyance networks in several areas of the U.S.o Southern California gets water from everywhere Northern CA ⇒ State water project Colorado River ⇒ Colorado Aqueduct Owens Valley ⇒ L.A. Aqueduct (“Chinatown”)o Denver, transfers from the West slope of the Rockies ⇒ East slope (e.g.,Colorado-Big Thompson project)o Phoenix/Tucson ⇒ Colorado River water conveyed via the CentralArizona Project- So, if it is becoming more expensive and more difficult to develop new sources of water, itmakes sense to begin to explore how we can use existing sources more efficiently.- If we are going to think about these issues we probably ought to know something about howwater is currently being used.SLIDE 8- Vast majority of consumptive water use in the U.S. is for irrigation- Most estimates indicate that less than half of the water diverted from rivers andstreams is actually put to productive use in crop growth, with the remainder beingattributable to:o Conveyance losseso Flood irrigation Runoff Seepage/evaporative losses- Most economists place the productive value of water in agriculture far below that of municipaland industrial uses- Presuming that we accept that the supply of water in U.S. is relatively fixed andpresuming that we want to continue to effectively support economic growth, wewould appear to have two optionso 1. Undertake conservation effortso 2. Transfer water to more highly valued activitiesSLIDE 9- While there is considerable anecdotal evidence that greater conservation efforts are being made,it is also clear that water is moving toward more highly valued activities (e.g., agricultural tourban transfers), a trend that is projected to continue.Texas1995 ⇒ 2050 Municipal and Industrial (M&I) use increases by half, even as the totalquantity of available water declines slightly.- This brings up policy-related questions as to how these transfers should take place,o 2 Extremes Government decides Turn water into private property and let people trade it like anyother commodity (i.e. market decides)- As with many things, the most practical solutions generally lay between these two extremes.- There is also the issue of society’s growing environmental awareness and the


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