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 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).

Forest Service & BLM Riparian buffer widths for federal lands are 150 ft 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.

State and private lands Riparian buffer 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.

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 are used to set the probability surface for those two ownership classes. 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.

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 established the following cropping systems for this study:

Orchards

Caneberries/Vineyards

Christmas Trees

Irrigated perennial

Nursery

Irrigated annual rotation

Grains

Grass seed-meadowfoam rotation

Hay

Pasture

Hybrid Poplar

Woodlot

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.

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 roken up 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:

Irrigation Interval ?= ( AWC ) ( MAD ) ( RDeff ) / Peak ETc?

Depth of Irrigation?= [ ( Irrigation Interval ) ( ETc ) / Ieff ] - P

?AWC?available water capacity

?MAD?management allowable depletion

?RDeff?effective root depth

?ETc?crop evapotranspriation

?Ieff?irrigation efficiency

?P?precipitation

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:

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:

We assume that future agricultural acreage allocation follow trends established over the last decade. These statistics show the acreage of most crop types increases slightly, with a larger increase in nursery operations and a decrease in grain acreage. Two crop types, hybrid poplar and woodlot, had no acreage information, and thus were only slowly phased into production, with small increases over time. In addition to crop acreage, water availability by WAB changes on a decadal basis. Using these constraints, each field, at the end of its rotation period, evaluates water and suitability conditions and acreage requirements, then selects a suitable crop type for that field.

County-level population projections are a major driver. We use population projections supplied by individual counties for cities and unincorporated areas. (or Metro for Clackamas, Multnomah, Washington counties supplemented by projections from individual cities, and LCOG for Lane County) In general, these county-originated population projections extend out to 2015 or 2020. We extend city forecasts to 2050 based on a declining positive in growth rate for individual cities, consistent with the DAS 2040 county-level projections for the area within the Willamette River Basin.

We are assuming no new rural residential zones will be created. We assume population increases up to 2020 will be accommodated within existing rural residential zones. We assume build-out of those areas by or before 2020 based on county population forecasts. We project a decrease in the size of rural residential zones due incorporation of some rural residential acres into UGBs, and therefor we assume some future rural residential county-wide population decreases by 2050.

Household size (persons per household or persons per dwelling unit) is based on US Census spatial data. Based on Metro projection of decreasing household sizes, we use a slightly decreased household size from 2020-2050 relative to 1990 household size.

Based on the number of existing industrial and commercial acres in 1990, we calculate the number of commercial acres needed and the number of industrial acres needed according to the DAS projections of employment by county. Existing 1990 commercial and industrial acres are derived from county tabular data and satellite imagery, and acres needed are calculated based on projected number of employees, with employee per acre ratios varying by county, increasing from the 1990 range of 15-27 employees per acre, to a range of 18 to 28 from 1990-2020 and 22 to 35 employees per acre from 2020-2050. Ratio of commercial and industrial employees for each city is based on the 1990 ratio of existing commercial and industrial acres in each city compared to county totals. We did not forecast growth in industrial and commercial acreage in unincorporated areas.

We did not forecast new dwellings in zones designated for agriculture or forestry use.

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.

We assess the supply of and demand for surface water in 178 "Water Availability Basins" (WABs), administrative/hydrological units defined by the Oregon Water Resources Department (OWRD). We compare supply and demand for each month.

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).

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.

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 second)

We allocate municipal demand within the constraints of the municipality's water rights and permits (if more than one) following historical patterns. For the Portland metropolitan area, we allocate the regional water demand scenario across active water rights, in order of priority. This allocation is intended only to illustrate the relationship between demand and supply, not to represent any commitment, formal or otherwise, to a specific allocation.

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.

We assume other demands remain fixed at the levels defined by current rights and permits.

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.

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.