1. Global Reach of Dams and Reservoirs
David Rosenberg
CEE 6490 – Integrated River Basin / Watershed Planning & Management

2. Learning Objectives Inventory global and US distributions of dams
Recognize time periods when dam building occurred
Demonstrate hydrologic, economic, and human impacts of dams

3. Distribution of large reservoirs
633 large reservoirs (Vorosmarty et al., 2003)

4. Gross figures of existing dams on Earth
45,000 dams are at least 15 m tall
They retain > 6500 km3 of water
5.3 Billion AF
15% of total global runoff
300 giant dams (> 150 m tall; >15 x 106 m3 dam volume; or, > 25 km3 storage)
Three Gorges Dam is largest dam on Earth
181 m tall
Stores > 39 km3 of water (32 MAF)

5. Degree of flow regulation
Ratio = reservoir storage / mean annual flow
Greatest flow regulation -- Volta (Africa) = 4.28)
Other significant regulation
Manicougan > 2.50
Colorado > 2.50
Rio Negro (Argentina) = 1.40
Euphrates-Tigris = 1.24
Mae Khlong (Thailand) = 1.30
(Nilsson et al., 2005)

6. Dam Databases ICOLD and IWPDC (worldwide registers of dams)
All dams > 15 m but many incomplete parts
~746 reservoirs with >0.5 km3 storage
Worldwide geographic data bases
UNESCO discharge data and runoff models

8. What is in the NID? All dams Data collected by USACE and FEMA
> 6 ft (2 m) tall with > 50 af (61,700 m3) storage
> 25 ft (8 m) tall with >15 af (18,500 m3) storage
that pose a “significant downstream threat”
Data collected by USACE and FEMA
Errors up to 4%

9. NID Findings
75,187 dams in U.S.
All watersheds larger than 2000 km2 have dams
Most dams are small
A few large dams store most surface water
(Graf, 1999)

10. NID Findings (cont.)
Northeast has greatest dam density (0.015 dams/km2)
Texas Gulf has greatest watershed fragmentation
Rio Grande and Lower Colorado most disrupt water and sediment
fluxes
(Graf, 1999)

11. NID Results (cont.)
Rio Grande and Lower Colorado have highest cost to supply additional water
California and Lower Colorado have many people and few dams
Lower Colorado has large reservoirs in relation to population
(Graf, 1999)

12. Reservoir construction over time in the U.S.
18,833 dams with 230 MAF of storage built in 1960s
(Graf, 1999)

13. Capacity expansion by region
Gradual increases
Accelerated periods of construction
Hoover Dam
Glen Canyon Dam
(Graf, 1999)

14. Research Activity
Questions: Is a country’s economic productivity correlated to water storage capacity in dams? How has water storage capacity changed with time for different countries?

15. Research Activity
Question 1: Is a country’s economic productivity correlated to water storage capacity in dams?

16. Research Activity
Question 1: Is a country’s economic productivity correlated to water storage capacity in dams?
Part 1, Individual Tasks:
Choose country and enter name into GoogleSheet:
Visit FAO Aquastat:
Find the GDP per capita and Dam Capacity per capita for your country for the most recently available time
Enter values into GoogleSheet

17. Research Activity
Question 2: How has water storage capacity changed with time for different countries?
Part 2, Individual Tasks:
For same country as part 1, use data from FAO Aquastat:
Find the total Dam Capacity (km3) for your country for all times available
Enter values into GoogleSheet

18. Impacts Altered flow regimes Sediment trapping Watershed fragmentation
Flood frequency and duration
Mean annual flow
Base (minimum) flows
Sediment trapping
Watershed fragmentation
Economic
Human

19. Nile River Discharge below the High Aswan Dam, Egypt
(Vorosmarty and Sahagian, 2000)

20. Colorado River below Glen Canyon Dam

21. Flow-Duration below Glen Canyon Dam
Pre-Dam (1921 – 1963)
Post-Dam (1963 – 2000)

22. Lower Colorado River Flow at Yuma

23. Indicators of Hydrologic Alteration
Magnitude of monthly water conditions
Magnitude and duration of annual water conditions
Timing of annual extreme water conditions
Frequency and duration of high and low pulses
Rate and frequency of water condition changes
(Richter et al., 1996)

24. Sediment Trapping by Large Reservoirs
(Vorosmarty et al., 2003)

25. Watershed Fragmentation
292 large river systems (LRS)
Basins with a virgin mean annual discharge (VMAD) > 350 m3/s (~12,000 ft3/s)
VMAD = most water-rich channel section
Drain 54% of world’s land mass
Fragmentation index:
Mainstem: 5 classes ~ longest main channel length without dams / entire main channel length
Tributaries: 3 classes (no dams, dams only on minor tribs, dams on major tribs)
(Nilsson et al., 2005)

26. Un-impacted
Moderately impacted
Strongly impacted
(Nilsson et al., 2005)

27. Human impacts 40 – 80 million people displaced
Millions more downstream suffer serious harm
Disproportionate impacts on indigenous & tribal people & ethnic minorities
(WCD, 2000)

28. Conclusions Inventory global and US distributions of dams
Recognize time periods when dam building occurred
Demonstrate hydrologic, economic, and human impacts of dams

29. References
Dynesius, M., and Nilsson, C Fragmentation and flow regulation of river systems in the northern third of the world. Science 226:
Collier, M. J., Webb, R. H., and Schmidt, J. C., 1996, Dams and rivers, primer on the downstream effects of dams: U.S. Geological Survey Circular 1126, 94 p.
Rosenberg, D., McCully, P., Pringle, C Global-Scale Environmental Effects of Hydrological Alterations: Introduction BioScience 50(9):
Vorosmarty, C. J., Sharma, K. P., Fekete, B. M., Copeland, A. H., Holden, J., Marble, J., and Lough, J. A The storage and aging of continental runoff in large reservoir systems of the world. Ambio 26 (4):

30. References (cont.)
Vorosmarty, C. J., and Sahagian, D., Anthropogenic Disturbance of the Terrestrial Water Cycle. BioScience 50(9):
Graf, W. L Dam nation: a geographic census of American dams and their large-scale hydrologic impacts. Water Resources Research 35 (4):
Vorosmarty, C. J., Meybeck, M., Fekete, B., Sharma, K., Green, P., and Syvitski, J. P. M Anthropogenic sediment retention: major global impact from registered river impoundments. Global and Planetary Change 39(1-2):
Nilsson, C., Reidy, C. A., Dynesius, M., and Revenga, C Fragmentation and flow regulation of the world’s large river systems. Science 308: