hydrology and water management ed maurer dept. of civil and environmental engineering univ. of...
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HYDROLOGY AND WATER MANAGEMENT
Ed MaurerDept. of Civil and Environmental EngineeringUniv. of Washington
FUNDAMENTAL QUESTIONS(FROM AN ENGINEERING PERSPECTIVE AT
LEAST)
•How much water is there?•How much water is needed?•What are the effects of water development?
Hydrologic cycle
Quantifying Water Supply - 1
USGS Gauge network provides daily measurements
Problems: missing data, don’t account for upstream conditions, errors at high flows
Long Term Variability
Case: The Colorado River
•18 years of data (1904-1922) showed 16-18 MAF•Long term records: 13.5 MAF and highly variable
Source: U.S. Bureau of reclamation.
A history of the PDO
warm coolwarm
A history of ENSO
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Pacific Decadal Oscillation El Niño Southern Oscillation
150000
200000
250000
300000
350000
400000
450000
190
0
191
0
192
0
193
0
194
0
195
0
196
0
197
0
198
0
199
0
200
0
Ap
r-S
ept F
low
(cfs
)
Effects of the PDO and ENSO on Columbia River Summer Streamflows
Cool CoolWarm Warm
Climate Change: Changes to Snow Extent and Naturalized Streamflow at The Dalles
Current
~2045
April 1 Snow Extent
20th CenturyNatural Flows
Estimated Range of Natural FlowWith 2040’s Warming
Depletions and “Natural” Flow
Colorado River below Hoover Dam, 1934-1970
Variability and Flow ReducedAverage Natural: 20.2 kcfsAverage Historic: 13.6 kcfs
Determining Natural Flow from Gauge Observations
1. Begin with historic measurements2. Account for timing changes due to
impoundment in reservoirs3. Add in irrigation diversion4. Subtract return flows from irrigation5. Add in evaporation from reservoirs6. This requires cooperation from
historians, agricultural experts, hydrologists, and others.
Quantifying Water Supply - 2
Where gauges aren’t available: use models
This has advantages such as:•Examine effects of past development (logging, roads)•Hypothetical case of return to natural (undisturbed) state•Evaluate future trends
Quantifying Water Supply -- Summary
To describe water supply we need to understand:•Hydrologic interactions between climate/weather, soil moisture, vegetation, snow, and streamflow•Slowly-varying signals in climate•Effects of watershed diversions and impoundments
Quantifying water needs
•Domestic, Municipal, Industrial
•Instream Flow
•Irrigation
Effects of Water DevelopmentLong-term effects can be unanticipated
• Excessive pumping of individual wells locally lowers the water table and creates a cone of depression around the well
• Subsidence may occur when water is withdrawn from aquifers in unconsolidated materials causing pore spaces to collapse
• Groundwater pollution may come from single point sources or distributed non-point sources including agricultural fertilizers, landfills, oil wells, mines, septic tanks, road salt and underground
Long-Term Pumping Effects
Santa Cruz River, Arizona
Groundwater pumping near the coast
Inland pumping can result in contamination of water wells near the coast with salt water
Large-scale water development
Multi-use reservoir on Tohono O’odham reservation, ArizonaRecreation, fish, wildlife, irrigation, groundwater rechargeWon Corps of Engineers distinguished design award, 1974
Actual ProjectMax. possible water height: 75 ft.
Peak level, 1974-2000: 15 ft.
Only gauged since 1998.
Design based on downstream measurements from 1954
Ephemeral flow difficult to measure
Seepage is difficult to predict
Diversions and Stream FlowSkokomish R.Dams built 1926-30
Simple Interaction of Diversions and Downstream Uses
0
200
400
600
800
1000
1200
1400
1600
1 2 3 4 5 6 7 8 9 10 11 12
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016flow
agricultural
Semi-hypothetical example using the S.F. Skokomish
System ModelMore complicated interactions and feedbacks of diversions and benefits.
Evaluate consequences of decisions using economic values of uses
Source: S. Lansing, U. Arizona.
Conclusions
•An understanding of hydrology is essential for quantifying water supplies and determining water needs.
•To satisfy water needs (and put water rights to use), priorities of uses must be established (instream/agricultural)
•Careful study of the interaction of different uses is needed to avoid conflicts
•Even carefully studied projects can have unanticipated consequences.
Timing in Water Requirements
•Phase shift between crop water (evapotranspiration) and stream flow
•Water requirement not met by precipitation is fed by diversion
•If diversion is not available, storage is needed.
•Reliability determined by variability of flows and size of storage
Precip.Evap..
Flow.