Section 2: MAP for the Large Scale Area

2. SIGNIFICANT CHARACTERISTICS OF THE LSA-NW

This section presents a brief summary about the LSA-NW which encompasses the Missouri River basin. The material was extracted from a more detailed description entitled "GCIP Studies in the LSA-NW" - A Discussion Paper which was compiled by David Meyer based on material provided by 25 contributors. A final draft of this document is being prepared and will be available through the GCIP Home Page when completed.

2.1 The LSA-NW Region

The LSA-NW, shown in Figure 2-1, encompasses the Missouri River basin which covers an area of more than one-half million square miles. The significant features of the LSA-NW include large year-to-year variability in water cycle components, significant regulation of stream flow through dams, major orographic influences from the Rocky Mountains relatively small runoff amounts, significant snow measurement problems, including snowmelt timing with regard to water budget components, and the Nebraska Sand Hills as a unique hydrology problem. The LSA-NW has other noteworthy features which include: extensive ground water transport through large aquifers such as the High Plains and Madison aquifers, the topographically-closed potholes of the northern prairie wetlands, and extensive karst topography in both the western and eastern regions of the Missouri River basin, all of which complicate estimates of basin-wide water budgets. As well, it encompasses some of the most extensively irrigated agricultural areas in North America, a feature whose impact on water and energy budgets, and thus climate, is largely unknown. The LSA-NW also combines several of the features of the other LSAs: it has a strong east-west moisture gradient, as in the LSA-SW; an extensive snow component in its water budget, as in the LSA-NC, and extensively managed waterways, as in the LSA-E.

2.2 Overview of the Missouri River Basin

Waters of the Jefferson, Madison, and Gallatin Rivers join to form the Missouri River near the town of Three Forks in southwestern Montana(see Figure 2-2). From this point at an elevation of about 4030 feet above mean sea level, the river's path traces slightly more than 2350 miles and drops nearly 3500 feet to its mouth at the Mississippi River 17 miles north of Saint Louis, Missouri. Together, the Missouri and its tributaries drain an area of nearly 532,000 square miles in the States of Montana, Wyoming, Colorado, North and South Dakota, Nebraska, Kansas, Minnesota, Iowa, and Missouri as well as small portions of the Canadian Provinces of Alberta and Saskatchewan.

The river is unique inasmuch as its path was largely defined by ice -- almost all of the terrain north and east of the Missouri River Valley has been extensively and repetitively glaciated during the past 1.6 million years. Most of the river's course marks ice margins of the last two glacial stages (Illinoisan and Wisconsin) along which melt waters scoured deep channels during warm periods. Consequently, for most of its course, the terrain, surficial geology and soils, ground and surface water hydrology, vegetation, and related microclimates change quite abruptly from one side of the river valley to the other.

Unlike the upper Mississippi River Basin, the upper part of the Missouri River Basin is drought prone while the lower part is flood prone. Also unlike the Mississippi River with its broad flood plains, the Missouri River is usually confined to a narrower, and generally steeper walled floodway in which bedload sediments are extensively reworked each spring by two flood pulses (late March and June) and transported downstream.

Figure 2-1. The LSA-NW Encompasses the Missouri River Basin.

Figure 2-2 Missouri River in the Context of the Upper Mississippi River basin.

The largest single program affecting water management within the Missouri River Basin was established by the Flood Control Act of 1944 and is known as the Missouri River Basin Project. Administered by the Bureau of Reclamation and U.S. Army Corps of Engineers, the project originally called for the construction of 137 dams and reservoirs to produce hydroelectric power, to check soil erosion, and to store millions of acre feet of water for irrigation and flood control affecting more than 10,000,000 acres of land. The dams also serve to maintain water levels in the lower Missouri's engineered navigation channel during periods of low runoff. To date, seven mainstem dams have been completed: Canyon Ferry (MT), Fort Peck (MT), Garrison (ND), Oahe (SD), Big Bend (SD), Fort Randall (SD), Gavins Point (SD/NE). Downstream of these structures, narrow, but fertile, floodplains have been "protected" by systems of levees constructed by the U.S. Army Corps of Engineers, the U.S. Department of Agriculture's Natural Resources Conservation Service, local governments, and private land owners.

The Missouri River Basin is physiographically, ecologically, and climatically diverse. Physiographic regions include portions of the Rocky Mountains Province (about 11% of the basin with 80 cm annual precipitation, mostly as snowfall) along the basin's western border, the Great Plains Province (about 70% of the basin with 45 cm annual precipitation) in the center, the Central Lowlands Province (about 17% of the basin with 75 cm annual precipitation) in the east and northeast, and the Interior Highlands Province (about 2% of the basin with 105 cm annual precipitation) in the extreme southeast.

Regional hydroclimatic processes and regimes within the basin are affected by many local variables, including topographic gradient and aspect; drainage pattern and density; soil texture, permeability, and water storage capacity; as well as land cover and associated land use and management practices. An important report (SAST, 1994) and WWW-based environmental database (URL: edcwww.cr.usgs.gov/sast-home.html) were prepared by the federally appointed Scientific Assessment and Strategy Team as two of many responses to the extensive flooding that occurred in the Midwest during the summer of 1993. This report summarizes characteristics of the Upper Mississippi River Basin (including the Missouri River Basin) as they relate to hydrology of mainstem floodplains and contributing upland areas and identifies several science issues that are germane to LSA-NW.

From the standpoint of surface hydrology, the Missouri River Basin is topographically characterized by two distinct kinds of landscapes based on their drainage networks: (1) open systems where runoff exits the basin by moving continuously from smaller streams to larger trunk streams, and (2) closed systems where runoff is temporarily trapped within closed depressions. Closed landscapes are genetically related to periglacial processes and spatially related to areas within the basin covered by younger glacial drift. These landscapes have not had sufficient time to develop an integrated network of streams and, consequently, trapped or ponded water must either evaporate or infiltrate. During large storms, however, smaller depressions may fill and spill over to lower level depressions or to segments of an integrated network of streams.

Before the widespread construction of open-ditch-type drainage ways for expanding agricultural practices within the basin, formerly closed landscapes acted as noncontributing areas with respect to surface water runoff. However, in several parts of the Missouri River Basin, artificially integrated systems function as open landscapes with respect to their influence on surface and ground water hydrology. Consequently, they need to be taken into consideration when modeling hydroclimatic processes and regimes within the basin. (SAST, 1994)

Soils are another hydroclimatically significant component of the Missouri River Basin because they act to store water and they affect rates of water runoff to streams, infiltration of water into the groundwater system, and the type, distribution, and success of vegetal land cover. Surface water storage in the basin is confined to the late-Wisconsinan glacial till area (the prairie pothole region) of North and South Dakota -- the rest of the basin consists of open systems with only minor areas that store water on the surface. By comparison, in other parts of the basin, estimates show 10 times more storage capacity in the soil than above ground. Subsoil storage is also important in the basin, but especially in open drained areas; subsoil storage is the major component and has relatively high capacities in Iowa, Missouri, Kansas, Montana, Colorado, and Nebraska relative to other States.

The Missouri River Basin includes 13 of 79 Level III Ecoregions of the conterminous USA based on Omernik's schema (U.S. Environmental Protection Agency, 1996). On the western edge of the basin, the Montana Valley and Foothill Prairies, Middle Rockies, Wyoming Basin, and Southern Rockies ecoregions host western coniferous forest, woodlands, and mixed forest dominated by pine, fir, aspen, juniper, sage, and annual grasses. In the northern, central, and southern portions of the basin, the Northwestern and Northern Glaciated Plains, Northwestern and Central Great Plains, Western High Plains, Nebraska Sand Hills, and Flint Hills ecoregions are dominated by savana grasslands and support both irrigated and dry land agriculture. On the eastern edge of the basin, the Western Corn Belt and Central Irregular Plains ecoregions are dominated by row crops, small grains, and mixed croplands and woodlands that include southeastern deciduous forest species. Throughout the basin, the associated vegetal species and their ecoregion context impose hydroclimatic effects related to evapotranspiration and related processes.

2.3 LSA-NW Infrastructure for GCIP Research

With respect to exploiting existing infrastructure and research efforts, the studies of the LSA-NW present both opportunities and challenges. The planned studies will include a pilot study by a group led by the South Dakota School of Mines and Technology who are addressing questions related to orographic effects on precipitation, especially in the cold seasons; coupled modeling to include deep groundwater in subsurface aquifers; and the effects of spatial and temporal variability at the Intermediate Scale Area (ISA) on atmospheric components in the water budget. This study itself relies on data from and ongoing Black Hills Hydrology study directed by the US Geological Survey's (USGS) Water Resources Division (WRD). In addition, the LSA-NW efforts can draw from studies undertaken in response to the extended flooding of the Missouri River basin in the 1990's, such as those of the Scientific Assessment and Strategy Team, a collaboration between several state and federal government agencies formed to assess the Missouri/Mississippi River basin flooding of 1993. Also, the LSA-NW will be the first basin-wide study to have access to new orbital remote sensing technologies, including the Landsat-7 enhanced Thematic Mapper plus (ETM+) system for detailed land cover and vegetation mapping, and the suite of surface and atmospheric observations to be provided by the Earth Observing System (EOS) AM-1 platform.

The challenges within LSA-NW arise from an in situ observation infrastructure that is less well developed than the other LSAs, particularly in the area of basin-wide surface energy and water vapor flux measurements. This problem must be addressed from three directions. First, improvements must be made to the existing infrastructure, through flux towers or other functionally similar observation strategies. Second, there will be an increased reliance on modeled quantities, which in turn relies heavily on model calibration and validation done in previous LSAs and the aforementioned pilot project. Finally, observations of surface and atmospheric processes will rely more heavily on remotely sensed data than was the case for the other LSAs.