The WRB Plan Trend 2050 future represents a straight-line projection of recent trends in mainstream zoning and land use to the year 2050. To the extent that long range plans indicate an intention of development and management trends, they are incorporated into the plan trend future. Forestry (e.g. Northwest Forest Plan) and urban land uses (e.g. Metro 2040 growth concept) provide examples of management and future growth plans which are incorporated into this scenario.
In the Plan Trend scenario, forestry and agriculture land uses cover the largest area in the WRB. Urban land uses have grown in areal extent relative to 1990 conditions with population growth accommodated by density increases in the Portland metropolitan area and the other large cities, including Eugene-Springfield, Salem-Keizer, and Albany-Corvallis. Residential densities also increase in the smaller cities and increase slightly in rural residential areas. Although by 2050 the population has doubled relative to 1990, the areas within urban growth boundaries have grown by approximately 50,000 acres (78 sq. mi.) from approximately 6% of the WRB area to 6.8%.
Willamette River Basin Population
Population projections for the PNWERC Alternative Futures Project for the Willamette River Basin (WRB) are based on Oregon Department of Administrative Services, Office of Economic Analysis population forecasts by county. These extend only to 2040, and PNWERC has extended the forecasts to 2050 using a regression line (rate of change.) The county forecasts have been adjusted to reflect the population within the area bounded by the Willamette River Basin based on 1990 population census blocks. The WRB's 1990 population is calculated to be 1,970,000 with 86% living within urban growth boundaries. The projected population for Plan Trend 2050, Conservation 2050 and Development 2050 is 3,900,000. In Plan Trend 2050, 93% of the population lives within urban growth boundaries; in Conservation 2050, 94% of the population lives within urban growth boundaries; and in Development 2050, 87% of the population lives within urban growth boundaries (Willamette River Basin Planning Atlas p.106).
A number of cities overlap the boundaries of two counties. County totals are combined for the purposes of calculating city and county projections where necessary.
Population forecasts for cities are based on Portland State University Center for Population Research data, supplemented by additional data from city and county governments ranging from 2020 to 2040. Where no outside sources exist, PNWERC extends the forecasts for the cities using individual city's rate of change, and matches county totals to within 1% of the DAS county total population. (details are available at: <http://www.fsl.orst.edu/pnwerc/wrb/metadata/ptpop.xls>)
To accommodate a doubling of the 1990 population, 2050 Plan Trend urban densities increase significantly relative to 1990 conditions. There is also expansion of urban areas from approximately 444,000 acres in 1990 to approximately 494,000 acres in 2050, with the comparative distribution of urban population and area in 2050 (north, mid, and south valley) consistent with the 1990 distribution.
Populations in unincorporated and rural residential areas were derived from county data, and calculated based on available buildable lands. New rural residences occur in Plan Trend only in areas zoned for rural residential use. These are fully built out by 2030 in this scenario. (details are available at: <http://www.fsl.orst.edu/pnwerc/wrb/metadata/ptpop.xls>)
Agricultural land use remains similar to 1990 conditions with increases in the nursery sector and in hybrid poplar which appears more frequently in suitable former pasture lands at low elevations. Grass seed remains a major crop, with orchards, berries, and Christmas trees in stable production. Riparian buffers increase along currently regulated (Oregon Senate Bill 1010 and Clean Water Act section 303d) water-quality limited streams. Under Plan Trend assumptions, 2050 riparian buffers increase approximately 10% over 1990 conditions, and consist of woody vegetation in agricultural lands dominated by Christmas trees, vineyards/caneberries and pasturelands, with grass filter-strips forming riparian buffers in irrigated fields and row crop agricultural lands. The total area of land in agricultural production remains at approximately 20% of the basin area in 2050, with approximately 20,000 1990 agricultural acres being converted to 2050 urban land uses in areas adjacent to 1990 urban growth boundaries.
Cropping Systems Selection:
The Willamette Valley supports a diverse selection of agricultural crops and management techniques. It is impossible to include all systems in our model, yet it is important to capture as much of the quality of this agricultural diversity as possible. To this end we modeled the following cropping systems for this study:
The rationale for this classification is to aggregate specific crops with similar characteristics into crop classes and, with these crop classes, into rotation systems if applicable. This allows us to capture major elements of the physical and management diversity of the agricultural system.
Irrigation Requirements: For simplicity, we assume the following crops always require irrigation, irrigated perennial irrigated annual rotation - row crop phase, caneberries/vineyards, nursery crops. All other crops are dryland. Additionally, the irrigated annual rotation is separated into an early season planting (April) and a late season planting (July) to better reflect irrigation planning options employed by growers.
Irrigation availability is a severe constraint in our model. For a given field, irrigation availability is computed for each crop prior to crop selection. If at any time during the growing season, there is forecasted to be inadequate irrigation, that crop type cannot be selected for that field. Monthly water requirements are computed assuming a non-varying irrigation schedule as follows:
Creation of the Agricultural Fields Coverage: The smallest decision unit for agricultural production is the field. We assume an agricultural field is greater than five acres in area, supports a homogeneous crop, and does not change spatial extent over time. To define the boundaries of agricultural fields we employ several different data sources:
Manually digitized polygons
USGS Water-Resources Investigations Report 97-4268 associated data polygons
OWRD Irrigation Place of Use polygons
ODFW Land Use/Land Cover polygons
PNW-ERC Vegetation Classification, generalized to a one-acre minimum mapping unit (mmu.) and defined as discrete polygons.
Taxlot parcels for selected counties
Initial Distribution of the Agricultural Classes: While several classifications of valley agriculture are currently available, no single classification contains all the classes listed above. Thus, it is necessary for us to integrate a variety of data sets in order to create an initial condition that reasonably reflects the current agricultural landscape under the constraints of crop types, irrigation requirements, and county-level distribution statistics . The data sets used are:
|A. PNW-ERC Vegetation Classification||1 acre mmu.||1993||Landsat Thematic Mapper data|
|B. ODFW Land Use/Land Cover data||1/3 acre mmu.||1993-1996||Fieldwork, Color Aerial Photos|
|C. PNW-ERC test polygons||Field||1993||Farm Service Agency 35mm slides|
|D. USGS Report 97-4268||Field||1996||Field Survey|
|E. Crop Suitability Data||1 : 24000||1998, vars.||SSURGO Soils data, NRCS Soil Surveys|
|F. Rural Zoning||1 : 100000||1986||DLCD|
|G. OWRD Irrigation Place of Use data||1 : 24000||1991-present||Digitized from water right applications|
|H. County agricultural statistics||County||1984-1998||Oregon Agricultural Statistics Service|
|I. OWRD Business Name||Tabular||Current||Water Resources Information System|
Modeled harvest units are 5.6 acres in size for private non-industrial lands. Willamette National Forest and Mt. Hood NF clear-cutting is based on the decadal harvest rates specified in their respective management plans using 30 acre clearcut patches. State and private industrial harvest units are 30 acres. The total area of 2050 land in forest remains at approximately 67 % of the basin area, similar to the 1990 percentage.
Management practices are modeled for five ownership classes: US Forest Service US Bureau of Land Management State of Oregon Private industrial Private non-industrial
All known reserves, wilderness areas and riparian buffers are withheld from harvest modeling
Harvest method - size of clearcut patch and frequency of harvest per unit space and time
Private industrial: The rates of clearcutting used for private ownerships are the average of the values reported for the years 1973-1995 by Lettman and Campbell in the May 1997 "Timber Harvesting Practices on Private Forest Land in Western Oregon."
Private non-industrial: Clearcut patches are 5.6 acres while all others are 30 acres (also from Lettman and Campbell, May 1997.)
Forest Service Data were available only for Willamette and Mt. Hood National Forests, no data available from Umpqua National Forest. All Siuslaw NF lands in the WRB are in Late Successional Reserves. For Willamette and Mt. Hood, harvest rates are given directly as decadal percentages in mapped zones in the digital datasets provided by those agencies.
BLM For all BLM lands the model incorporated the results of a forest management model generated by the Eugene BLM district, showing clearcut acres in each of a range of forest age classes for each of a series of decades nearly coextensive with those used in Plan Trend modeling.
Note: we are unable to model selective cutting, which is used about two-thirds of the time on private non-industrial lands and three-quarters on private industrial lands (Lettman and Campbell, 1997).
Riparian zones Forest Service & BLM Riparian zone widths for federal lands are 300ft on each side of streams, based on the Northwest Forest Plan Option Nine values. Stream locations were determined by the latest available results of stream mapping efforts underway in the federal agencies at the time of modeling.
State and private lands Riparian zone widths are 70 ft on each side of streams, and stream locations were derived from the PNW River Reach dataset as amended by the ERC.
Probability "surface" based on the age of the pre-harvest trees: In the simulations, the pattern of forest age is influenced by use of a probability "surface" based on the age of the pre-harvest trees. During simulation, clearcut patches are distributed over the landscape in such a way that more of them will appear in locations with a high probability surface value. For private forest lands, the relationship between forest age and probability of harvesting is derived from tables published in Lettman and Campbell. For BLM, the harvest percentage by forest age class table provided in the BLM model is used to set the probability surface. For USFS lands, the stated harvest frequencies are used directly as the probability surface values. For State lands, digital maps provided by the Oregon Dept. of Forestry were used to define state ownership and to identify areas withheld from commercial logging. Clearcutting on lands managed by the Oregon Dept. of Forestry is modeled at the same age-dependent rate as for the Private Industrial ownership class.
With forestlands continuing to occupy more than two-thirds of the basin, upland natural vegetation remains extensive under Plan Trend 2050 assumptions. While few explicit assumptions were stated in Plan Trend regarding natural vegetation outside state and federally managed forest lands, land and water use and management affect natural vegetation throughout the WRB, primarily through land conversion to urban uses, agricultural activity, reservoir management, and forest management.
The Plan Trend 2050 Scenario evaluates the economic pressure on water resources by assessing the supply of and demand for water in 178 "Water Availability Basins" (WABs), an administrative/hydrological unit defined by the Oregon Water Resources Department (OWRD). We compare supply and demand for each month.
The supply of surface water is represented in three sub-scenarios: a "normal" year, and a "dry" year, and a "wet" year. The supply is assumed to be insensitive to changes in the landscape, so the three sub-scenarios of supply are the same across time, and across the alternative futures.
The demand for surface water is represented by existing surface water rights and permits. Demand for surface water is summarized in six categories:
Under all three sub-scenarios, mean annual flows remain unchanged in 140 WABs and decline in about 36 WABs: up to 3 percent under the "dry" sub-scenario and up to 1 percent under the "normal" sub-scenario, relative to 2000.
Objectives: To compare the supply of surface water in the Willamette River Basin with the competing in-stream and out-of-stream demands, and to gauge the extent to which the demands are likely to increase by 2050.
Supply of Surface Water: The supply predictions stem from OWRD's estimates of the probability distribution of what natural streamflows would be, absent consumptive withdrawals, at the pour point of each WAB. We examine three sub-scenarios: "normal" (based on median flows in each WAB, i.e., flows exceeded 50 percent of the time); "dry" (based on flows exceeded 80 percent of the time); and "wet" (based on flows exceeded 20 percent of the time).
Competition for Surface Water: We assume that existing water rights and permits will persist until 2050, and that OWRD will issue new permits only for small rural self-supplied users and along the mainstems of the Lower McKenzie and Willamette Rivers. We consider six types of demand: municipal; reservoirs (federal and private); in-stream, irrigation; industrial; and other. We assume that all types of demand, except municipal and self-supplied domestic, remain fixed at the levels determined by current rights and permits.
Municipal and Self-Supplied Domestic Demand:
To estimate future water use in the Portland area we rely on a water-use scenario developed by regional water
providers circa 1992. For the remainder of the Basin we assume these types of demand are the product of population
times a per-capita-use coefficient. Municipal demand is consolidated for the entire area within each urban growth
boundary (UGB), and self-supplied domestic demand is estimated for the area of each county outside UGBs.
Per Capita Diversion Rates Outside the Portland Area (cubic feet per
|JAN 0.00037 cfs||JUL 0.00060 cfs|
|FEB 0.00037||AUG 0.00060|
|MAR 0.0003||SEP 0.00050|
|APR 0.00039||OCT 0.00041|
|MAY 0.00041||NOV 0.00039|
|JUN 0.00050||DEC 0.00037|
Reservoir Demand: We assume the Army Corps of Engineers will store water according to the patterns exhibited during recent years typical of dry, normal, and wet conditions. We assume private reservoirs will fill once each year, to the maximum allowed in the right or permit, with diversions spread proportionately from November to February. Water released from federal reservoirs will remain available for purchase from the Bureau of Reclamation, but not for appropriation by downstream users. We assume water released from private reservoirs is consumed before it can return to the stream.
In-Stream Demand: We assume other demands remain fixed at the levels defined by current rights and permits.
Diversion and Consumption Rates:
The diversion rate is the flow claimed for each use allowed by a right or permit. The consumption rate is the percentage
of the diversion that is extracted and not returned to the stream. Except for municipal demands, we assume that the
holder of each right or permit diverts water to the intended use at the full rate allowed. The consumption rate varies by
type of demand.
|Diversion Rate (% of water right or permit)||Consumption Rate (% of water diverted)|
|In-Stream||100% ("diversion" = remains in stream)||0%|
|Irrigation||100%, or rate estimated by irrigation model||50%|
|Municipal||Equals population times per capita rate||45% (summer)
|Miscellaneous||100%||varies, from 0-50%, by type of use|
Order of Allocation: We allocate water sequentially by the priority date of each right or permit until all have been satisfied or the supply has been exhausted. A downstream right or permit may restrict upstream water uses associated with lower-priority rights or permits.
Lettman, J. G., and D. Campbell. 1997. Timber Harvesting Practices on Private Forest Land in Western Oregon. Oregon Department of Forestry Forest Resources Planning Program. 48p.
Hulse, D., S. Gregory and J. Baker, editors, Willamette River Basin Planning Atlas, Oregon State University Press, Corvallis, Oregon, 2002.