Volume 1/Chapter 2/People and Resource Use

* Critical Findings

Settlement in the Sierra

* Deforestation in the Mid-1800s

Resource Use: Changing Needs Through Time

Regional Economies

* Social and Economic Analysis

Community Well-Being in the Sierra

MANAGEMENT SCENARIOS AND STRATEGIES

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Scenarios

Without assuming any linkages to specific policies or market conditions, six alternative distributions of future population by housing density class were considered. These were based upon GIS analysis of the distribution of population by housing density class under the following: (1) 1990 Sierra Nevada census blocks; (2) 1990 Nevada County census blocks; (3) 1990 El Dorado County census blocks; (4) Nevada County General Plan; (5) El Dorado County General Plan Project Description; and (6) El Dorado County General Plan Alternative. The three General Plan distributions were based on the planimetric estimates of area designated for buildout at specific density classes in the General Plan land-use maps but did not account for the greater development in some density classes that is likely to take place due to existing parcelization. They therefore overstate the degree of future concentration.

Four alternative future growth projections from 1990 to 2040 were considered for each of the forty-six county census divisions (CCDs) in the analysis: (1) based on each CCDs 197090 share of overall county growth; (2) based on each CCDs 197080 share of overall county growth; (3) based on each CCDs 198090 share of overall county growth; and (4) a lower projection at two-thirds the first described projection, which was the approximate absolute growth rate historically from 1970 to 1990 for the entire Sierra Nevada. Combined with the six alternative population distributions by density class, these four alternative population projections for 19902040 result in twenty-four possible land-conversion estimates for each of the forty-six CCDs in our analysis for the year 2040. The resulting 1,104 cells of land-conversion estimates are a bit overwhelming for presentation, however, and many of the population distributions by housing density class are similar to one another. Therefore, the set was simplified to four scenarios:

Low population growth with compact human settlement patterns (Low-Compact)
High population growth with compact human settlement patterns (High-Compact)
Low population growth with sprawling human settlement patterns (Low-Sprawl)
High population growth with sprawling human settlement patterns (High-Sprawl)

The most compact population distribution was the Nevada County General Plan, in which 71.3% of the population is accommodated in the highest housing density class (640+ dwelling units per square mile). Note that this is a significantly higher fraction of the population than there was in this class in 1990, when Nevada Countys distribution was not significantly different from that for the entire Sierra Nevada (figure 2.13). The compact distribution assumed in the Nevada County General Plan still consumes roughly a quarter-acre per person in the highest housing density class in an average of roughly two dwelling units per acre. This compact pattern is therefore considerably less dense than most suburban subdivision densities in metropolitan areas. This pattern likely reflects a bimodal distribution within this density class, where there are clusters of parcels close to one acre in size (with on-site domestic well water and on-site wastewater disposal through septic systems) and around one-quarter acre in size (with public water and sewer). Unfortunately, it was not feasible to disaggregate housing density below this level for the analysis. Doubling the average density for this class (through an infrastructure-directed development strategy) could reduce the land conversion estimates for the compact scenarios by 50% in the highest-density class. It would have little effect, however, on the total land area converted by human settlement at any of the lower thresholds for human settlement. As noted in the more detailed assessment, the Nevada County General Plan also underestimates the amount of land that is likely to be developed at lower densities due to existing parcelization. The quarter-acre-per-person estimate for the highest housing density class is therefore a reasonable basis for estimating the land-conversion effects of compact human settlement patterns across the entire Sierra Nevada.

FIGURE 2.13a (ACTUAL VIEW 44K)

FIGURE 2.13b (ACTUAL VIEW 44K)

Projected change in relative housing density, El Dorado County, from 1990 to buildout, based on General Plan alternatives. (From volume II, chapter 11.) Top: Projection based on primary project model. Bottom: Projection based on alternative project model.

The most dispersed (sprawl) population distribution was the 1990 Sierra Nevada census block distribution, in which 39.5% of the population resided in the highest housing density class. We therefore assumed continuation of this existing distribution across all CCDs in the Sierra Nevada for our sprawl scenarios of human settlement. This assumption allowed us to estimate the total land area required in each CCD to accommodate 1990 to 2040 population growth if existing patterns of human settlement were to continue. Land tenure relationships constrain the potential to expand the land area converted to lower housing density classes, however, so the lower housing density classes generally increase their average densities within their density ranges rather than expand in area (e.g., land in the class with ten to twenty dwelling units per square mile might move from twelve dwelling units to eighteen per square mile). This analysis therefore estimated land converted to human settlement only above the density threshold of twenty dwelling units per square mile (32 acres per dwelling unit).

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