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Water Resource Impacts of Low and High Density Residential Development: A Comparative Analysis

Water Resource Impacts of Low and High Density Residential Development: A Comparative Analysis. Dr. David Gallo Department of Economics and The Center for Economic Development California State University, Chico. Impacts Assessed. Cost of water-related infrastructure: water and sewer

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Water Resource Impacts of Low and High Density Residential Development: A Comparative Analysis

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  1. Water Resource Impacts of Low and High Density Residential Development: A Comparative Analysis Dr. David Gallo Department of Economics and The Center for Economic Development California State University, Chico

  2. Impacts Assessed • Cost of water-related infrastructure: water and sewer • Water consumption • Runoff

  3. Development Densities Compared • Low density residential: three units per acre • High density residential: ten units per acre

  4. Scale of Development • Use the Meriam Park development proposed by New Urban Builders for Chico, California • A mixed use development of 2300 homes • To be built on 272 acres for a gross density of 8.45 units per acre • 210 of those acres are to be developed for a net density of 10.95 units per acre

  5. Water and Sewer Costs: High Density • Data from American Planning Association, EPA, and other sources • Annual cost of water and sewer infrastructure: $891 per household • 30-year cost per housing unit: $26,730 • 30-year cost for 2300 housing units: $61,478,000

  6. Water and Sewer Costs: Low Density • Higher annual infrastructure cost per housing unit: $1,133 • At three units per acre the 272 acres in the Meriam Park development would only accommodate 30% of the housing • Additional housing is assumed to be 0.5 miles further from the urban core. • The added cost per unit for these more remote low density units is $21.00 annually

  7. Total Cost for 2300 Housing Units: Low Density Development Pattern • 690 units with annual water and sewer costs of $1,133 • 1610 units with annual water and sewer costs of $1,154 • Total annual cost per housing unit: $1,148 • 30-year cost per housing unit: $34,440 • 30-year cost for 2300 housing units: $79,218,000

  8. Water and Sewer Infrastructure Cost Savings: Low vs. High Density Development Patterns

  9. Per Capita Water Use • Data from a study in Envision, Utah • At 3 units per acre, per capita use is 160 gallons per day • At 7 units per acre, per capita use is 100 gallons per day • Little or no further reduction is achieved at higher densities

  10. Annual Household Water Use • Assume 2 individuals per household • Annual use for three units per acre: 116,800 gallons (.36 acre feet) • Annual use at seven or more units per acre: 73,000 gallons (.22 acre feet)

  11. Total Annual Water Use for 2300 Housing Units • High Density: 515 acre feet annually • Low Density: 824 acre feet annually • Annual savings: 309 acre feet

  12. Value of Water Use Reduction • Water Value of $120 per acre foot • Based on the price of water transfers north of the delta • Similar to the cost of water from proposed new storage projects • Annual value is $37,100 • 30-year savings of $1,113,000

  13. Watershed Impacts: Annual Runoff • Estimates based on the EPA’s SG WATER model • Basis for the estimates is the amount of impervious surface • Comparison is for four and eight units per acre

  14. Impervious Surface: Percent of Developed Land • Four units per acre: 38 percent is impervious surface • Eight units per acre: 65 percent is impervious surface

  15. Total Impervious Surface • Four units per acre and 2300 homes: 219 acres of impervious surface • Eight units per acre and 2300 homes: 187 acres of impervious surface • Also, lawn areas are more impervious than undisturbed watershed

  16. Annual Runoff per Housing Unit • Four units per acre: 6200 cubic feet • Eight units per acre: 4950 cubic feet

  17. Annual Runoff for 2300 homes • At four units per acre: 327 acre feet • At eight units per acre: 261 acre feet • Reduction in runoff for high density development: 66 acre feet per year

  18. Summary for 2300 Housing Units: Water-Related Benefits of High Density Residential Development • Reduced cost of infrastructure for water and sewer: 30-year total of $17,739,000 • Reduced water use: Annual reduction of 309 acre feet for a 30-year savings of $1,113,000 • Reduced runoff: Annual reduction of 66 acre feet

  19. Statewide Impacts • It is expected that California will add approximately 4 million households by 2025 • High density residential development patterns will achieve the following: • Reduce water and sewer infrastructure cost by $30.85 billion over 30 years • Reduce annual water use by 538,000 acre feet • Reduce annual runoff by 115,000 acre feet

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