Global
Reservoir and Dam (GRanD) Database
Project Summary, July 2008
B. Lehner, B. Fekete, C. Reidy, C. Vörösmarty
Reservoirs play an important role in the capacity
to control and manage global water resources. Dams and impoundments
have been built by humans for hundreds or even thousands of years
and for various purposes, including flood control, water supply,
irrigation, recreation, navigation, fisheries, and the generation
of hydropower (WCD 2000). Yet it was only in the last few decades
that the number of dams has significantly increased, reaching an
estimated 50000 large dams in operation worldwide (ICOLD 2007; large
dams defined as being higher than 15 m). These reservoirs have a
cumulative storage capacity of more than 7000 km3 (ICOLD 2007; updated
to 8300 km3 by Chao et al. 2008) representing approximately one-fifth
of the total annual runoff from land (Hanasaki et al. 2006). Smaller
impoundments are not taken into account in these estimates as there
are no reliable global figures available. Estimates and extrapolations,
however, suggest that several million smaller impoundments have
been built in the US alone (Renwick et al. 2005), with a cumulative
storage capacity that may be in the same order of magnitude as that
of large reservoirs.
Intrinsically, dams and reservoirs alter the hydrologic
conditions of a river system, including changes in the flow regime,
in water quality, and sediment transport. These alterations may
impair the hydro-ecological integrity of the affected river systems
(Poff et al. 2007), fragment aquatic habitats (Nilsson et al. 2005),
increase the aging of water (Vörösmarty et al. 1997),
cause the emission of greenhouse gases (St. Louis et al. 2000) and
reduce the sediment and nutrient transport to the world’s
oceans (Syvitski et al. 2005). Effects of reservoirs are often far
reaching; both downstream and upstream (e.g., when impeding fish
migration).
Despite their importance, global data sets describing
the characteristics and geographical distribution of reservoirs
and dams worldwide are notoriously incomplete. The most comprehensive
database, the World Register of Dams, is compiled by the International
Commission on Large Dams (ICOLD) and provides approximately 50000
records of large dams (ICOLD 2007) and their attributes. Unfortunately,
this inventory does not include the geographical location of the
dams, which renders it of limited use for many scientific applications.
Studies on water resources management typically need to allocate
reservoirs to sub-basins, link them to the drainage network, or
relate them to population centers and irrigated areas, both on local
and global scales.
For this reason hydrological modelers and water resources
planners have begun to develop their own data sets of the global
distribution of dams and reservoirs, mostly by identifying the largest
of them on paper maps and compiling attribute information from various
sources including national archives and the internet. In tedious
manual processes they have created several global and regional data
sets. Unfortunately, these databases are typically limited in their
number of records, their spatial resolution, and their general reliability
of attribute data. Geographically, the dams have been referenced
to basins, sub-basins or within coarse grids, while only two data
sets include the actual polygons of the reservoirs. The most extensive
publicly available compilation contains approximately 1500 large
reservoirs.
In 2006, the Global Water System Project (GWSP) initiated
an international effort to collate the existing dam and reservoir
data sets with the aim to provide a single, reliable database for
the scientific community. Coordinated by GWSP, experts from twelve
institutions collaborated in the project (Table 1). Protocols were
designed in a series of workshops to combine and clean the original
data sets and to spatially reference the entries in a Geographic
Information System (GIS). The final consolidation of a new database
was led by McGill University and the University of New Hampshire,
resulting in a new product: the Global Reservoir and Dam (GRanD)
Database.
The development of the GRanD Database primarily aimed
at compiling all reservoirs with a storage capacity of more than
0.1 km3. Yet in the actual work flow, many smaller reservoirs in
the range between 0.1 and 0.01 km3 were included. In the process
of cleaning and consolidating the various data sets, many errors
were corrected and lacking data was completed, either by comparing
and merging attributes from different databases, or by consulting
and adding independent sources of information. A major issue was
the identification of duplicates. Duplicate entries can occur when
multiple dams form one reservoir; a dam is updated in time at the
same location; or the same dam or reservoir is erroneously listed
several times in one or more databases, often with inconsistent
names and attributes.
Within a GIS environment, the dams were geo-referenced
guided by paper and digital maps, atlases and visual inspections
of remote sensing imagery (foremost Google Earth). As a key characteristic
of GRanD, nearly all dams could be referenced to corresponding polygons.
Most polygons were depicted from the Surface Water Body Database,
a near-global mapping product created at 30 m resolution (NASA/NGA
2003). Some additional polygons were added from various alternative
sources, or digitized from scratch. Finally, the coordinates of
the dam locations enable a direct linkage to HydroSHEDS, a near-global
digital river network at 90 m resolution (Lehner et al. 2008), which
provides up- and downstream topology to the reservoirs.
The GIS implementation led to various important advantages.
It related dams to reservoirs, thus eliminating the confusion of
duplicates; it supported additional error checking as attributes
could be evaluated regarding their physical feasibility (e.g., recorded
reservoir surface area vs. polygon area); and it allowed for the
derivation of additional attributes by overlaying the dam and reservoir
locations with auxiliary geospatial data. For example, the elevation
of the lake surface or the contributing watershed area can be derived
from HydroSHEDS data. More sophisticated attributes are conceivable
in the future, such as modeled river inflow for each reservoir.
Version 1 of the GRanD Database contains approximately
7000 records of reservoirs and their dams, with a cumulative storage
capacity of approximately 5500 km3. The attribute data include (in
most cases) the dam and reservoir name, country, coordinates, reservoir
surface area (recorded; and derived from polygon), storage capacity,
dam height, main purpose of the reservoir, elevation (m.a.s.l.),
and derived watershed area (based on HydroSHEDS). Currently, the
beta version is verified by the contributing researchers. After
final clarification of remaining copyright issues it is aimed to
offer the GRanD Database to the scientific community by the end
of 2008.
Table 1: Institutions that participated in the development of the
GRanD Database, their provided data sets, and the particular regions
they focused on within the project.
Institution Provided data Focus of contribution
University of Frankfurt, Germany Global China
University of Greifswald, Germany Global Europe
University of Kassel, Germany Global
University of New Hampshire, USA Global North America
University of Umea, Sweden Global
University of Yamanashi, Japan Global Japan
World Wildlife Fund (WWF), USA Global Asia
The Nature Conservancy (TNC), USA South America South America
Food and Agriculture Organization (FAO) Africa
European Environmental Agency, Denmark Europe
King’s College London, UK Tropical regions Caribbean
McGill University, Canada Global
References
Chao, B.F., Wu, Y.H., Li, Y.S., 2008. Impact of artificial
reservoir water impoundment on global sea level. Science 320, 212–214.
Hanasaki, N., Kanae, S., Oki, T., 2006. A reservoir operation scheme
for global river routing models. Journal of Hydrology 327, 22–41.
ICOLD (International Commission on Large Dams), 2007. World Register
of Dams. ICOLD, Paris. Available at www.icold-cigb.net
Lehner, B., Verdin, K., Jarvis, A., 2008. New global hydrography
derived from spaceborne elevation data. Eos Transactions 89(10),
93–94.
Nilsson, C., Reidy, C.A., Dynesius, M., Revenga, C., 2005. Fragmentation
and flow regulation of the world’s large river systems. Science
308, 405–408.
NASA/NGA, 2003. SRTM Water Body Data Product Specific Guidance,
Version 2.0. 4pp. Available at http://edc.usgs.gov/products/elevation/swbdguide.doc
Poff, N.L., Olden, J.D., Merritt, D.M., Pepin, D.M., 2007. Homogenization
of regional river dynamics by dams and global biodiversity implications.
Proc. Natl. Acad. Sci. USA 104, 5732–5737.
Renwick, W.H., Smith, S.V., Bartley, J.D., Buddemeier, R.W., 2005.
The role of impoundments in the sediment budget of the conterminous
United States. Geomorphology 71, 99–111.
Syvitski, J.P.M., Vörösmarty, C.J., Kettner, A.J., Green,
P., 2005. Impact of humans on the flux of terrestrial sediment to
the global coastal ocean. Science 308, 376–380.
St. Louis, V.L., Kelly, C.A., Duchemin, E., Rudd, J.W.M., Rosenberg,
D.M., 2000. Reservoir surfaces as sources of greenhouse gases to
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Vörösmarty, C.J., Sharma, K.P., Fekete, B.M., Copeland,
A.H., Holden, J., Marble, J., Lough, J.A., 1997. The storage and
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WCD (World Commission on Dams), 2000. Dams and development: A framework
for decision making. Earthscan, London, UK, 404pp.
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