Goal PH 1 - To phase development within a designated urban growth area in two tiers: a first tier providing land supply for a ten-year projected population, with infrastructure and service costs shared by the public at large and new development; and a second tier beyond the ten-year supply allowing for development and paying for the full cost of infrastructure and services. Policy PH 1.1 Determine acreage needed for the ten-year and twenty-year projected population growths, based on urban density guidelines and urban open space and public park needs.
Policy PH 1.2 Establish ten-year and twenty-year urban growth boundaries from lands not permanently set aside as open space and public parks. Urban growth boundaries may be adjusted to reflect adopted changes in population forecasts.
Policy PH 1.3 Plan and fund facilities and services like sewer and water within the ten-year urban growth boundary, allowing development beyond the boundary only if it fully pays for its costs.
Figure 3 Airport Clear Zones
Policy PH 1.4 Encourage growth in the first tier areas before expanding to second tier areas.
Policy PH 1.5 Utilize highway and road system improvements to assist in managing and directing growth:
Give highest priority to street improvements within the existing City limits.
Assume maintenance of current facilities and ability to maintain highway/facility extensions before making area improvements.
Financing Development Policies Policy PH 1.6 Residential developers should assume all direct costs of their individual projects; such as roads, accesses, parking, surface drainages, water systems, sewer systems, etc. The general taxpaying public of the City should not be required to pay those costs in future years due to lack of, or inadequate, initial construction.
Policy PH 1.7 Assure equitable cost-sharing for new growth by utilizing techniques such as current-use tax assessment, or the purchase of development rights.
Monitoring Goal MN 1. – To ensure that sufficient land use capacity is available to accommodate the GMA population allocation while still meeting the community’s and region’s need for economic development, public facilities and amenities, and other land uses. Policy MN1.1: Monitor growth and development within the city to evaluate whether sufficient capacity exists to accommodate population growth without reducing the capacity for other needed and beneficial uses.
Strategy MN 1.1.1: Conduct this monitoring in conjunction with monitoring the adequacy of public facility capacity to support growth (Policy LOS 1.4 of the Capital Facilities Element) to ensure the land use plan and the capital facilities plan remain internally consistent. Policy MN 1.2: Apply one of the following strategies whenever it may appear that there is insufficient capacity to accommodate the GMA population allocation while responding to other community needs:
Strategy MN 1.2.1: Consider designating urban reserve areas for residential uses.
Strategy MN 1.2.3: Consider converting area designated for other uses for residential areas, unless appropriate for mixed uses.
Strategy MN 1.2.4 Consider allowing mixed residential uses in other land use designations. Environmental Protection Since the conservation, protection and enhancement of environmental resources are activities that affect the use of various areas within the City, the land use element incorporates these activities, as well as measures to protect developed uses from environmental hazards.
The following goals, policies and strategies are intended to promote the preservation of critical areas within the City of Prosser’s Urban Growth Area while striking a balance between property rights and the regulation thereof through critical areas regulations.
General Environmental Management
Goal EV 1. To preserve the environment when possible. Policy EV 1.1 Protect wildlife habitats as designated open space and wetland areas.
Strategy EV 1.1.1. Base the protection methodology on the size, location and vulnerability of the wildlife habitat and species. Strategy EV 1.1.2. Acquire and protect key significant wildlife habitat areas.
Strategy EV 1.1.3. Ensure the preservation of a variety of habitat types, sizes and locations. Strategy EV 1.1.4. Regulate any filling or the disturbance of wetlands and wetlands vegetation and the surrounding buffer.
Strategy EV 1.1.5. Inventory, classify, designate, and adopt regulations that will preserve and protect wetlands with no net loss of this resource.
Strategy EV 1.1.6. Seek and promote non-regulatory measures to enhance and conserve critical area values and functions, including public education, stewardshipprograms, grant opportunities, partnerships with other jurisdictions and non-profit organizations, etc. Strategy EV 1.1.7. Designate and conserve the following areas as fish and wildlife critical areas:
Areas which have a primary association with state or federally designated endangered, threatened, and sensitive species,
Habitats of local importance including, but not limited to, areas designated as priority habitat by the Department of Fish and Wildlife,
Naturally occurring ponds under twenty acres and their submerged aquatic beds that provide fish or wildlife habitat, including those artificial ponds intentionally created from dry areas in order to mitigate impacts to ponds,
Waters of the state, including lakes, rivers, ponds, streams, inland waters, underground waters, salt waters and all other surface waters and watercourses within the jurisdiction of the state of Washington,
Lakes, ponds, streams, and rivers planted with game fish by a governmental or tribal entity,
State natural area preserves and natural resource conservation areas; and
Land essential for preserving connections between habitat blocks and open spaces.
Policy EV 1.2. To preserve natural drainage ways.
Strategy EV 1.2.1. Promote public awareness of the natural drainage ways, their role in the area, and the importance of maintaining natural drainage systems.Strategy EV 1.2.2. Establish standards for the retention, recharge, and treatment of storm water runoff channeled from impervious surfaces.
Strategy EV 1.2.3. Designate as "Frequently flooded critical areas" lands in the floodplain subject to a one-percent or greater chance of flooding in any given year and those lands that provide important flood storage, conveyance and attenuation functions, as determined by the City in accordance with WAC http://nt5.scbbs.com/cgi-bin/om_isapi.dll?clientID=288320&headingswithhits=on&hitsperheading=on&infobase=wac.sdw&jump=365-190-080&softpage=PL_Doc - JUMPDEST_365-190-080365-190-080(3). Frequently flooded areas perform important hydrologic functions and may present a risk to persons and property. Classifications of frequently flooded areas include, at a minimum, the one-hundred-year floodplain designations of the Federal Emergency Management Agency and the National Flood Insurance Program. Strategy EV 1.2.4. Regulate development within the frequently flooded critical areas or other flood hazard areas of the city in accordance with the national Flood Insurance Program. Policy EV 1.3. To regulate development in geologically hazardous areas.
Strategy EV 1.3.1. Designate as “Geologically hazardous” critical areas, areas that may not be suited to development consistent with public health, safety or environmental standards because of their susceptibility to erosion, sliding, earthquake, or other geological events. Types of geologically hazardous areas include: erosion, landslide, seismic, mine, and volcanic hazards.
Strategy EV 1.3.2. Require engineering, architectural, or geo-technical investigations and certifications of approval of development permits or authorizations to proceed in hazardous areas.
Policy EV 1.4. Prevent isolation of communities of endangered, threatened or sensitive species.
Policy EV 1.5. Protect surface water and groundwater supplies.
Strategy EV 1.5.1. Identify and designate as "Aquifer recharge critical areas" lands that, due to the presence of certain soils, geology, and surface water, act to recharge ground water by percolation Strategy EV 1.5.2. In aquifer recharge critical areas restrict development (except for City wells) that significantly degrades or depletes surface waters or groundwater. Goal EV 2. To enhance the environment where possible. Policy EV 2.1. Provide incentives for the restoration of degraded wetlands, watercourses and other important natural systems.
Goal EV 3. To mitigate adverse environmental impacts.
Policy EV 3.1. Mitigate all adverse impacts to wetlands defined as areas that are inundated or saturated by surface water or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas. Wetlands do not include those artificial wetlands intentionally created from nonwetland sites, including, but not limited to, irrigation and drainage ditches, grass-lined swales, canals, detention facilities, wastewater treatment facilities, farm ponds, and landscape amenities, or those wetlands created after July 1, 1990, that were unintentionally created as a result of the construction of a road, street, or highway. Wetlands may include those artificial wetlands intentionally created from non-wetland areas created to mitigate conversion of wetlands.
Policy EV 3.2. Designate all wetland areas by applying the Department of Ecology’s wetland delineation manual.
Policy EV 3.3. Require the mitigation of impacts from development adjacent to sensitive areas.
Policy EV 3.4. Encourage the creation and maintenance of non-regulated wetland areas.
Goal EV 4. To minimize the impacts of development to property owners while not adversely impacting critical areas. Policy EV4.1. Use density bonuses and other means of compensation as appropriate for the protection of critical areas.
Best Available Science
Goal BA 1. To protect the functions and values of critical areas by using best available scientific information to: Policy BA 1.1. Use the best available science in all aspects of managing critical areas including developing regulations, delineating critical areas, identifying functions and values, and recommending strategies to protect their functions and values.
Strategy BA 1.1.: Recognize that best available science is science that applies valid scientific methods consisting of research conducted by qualified individuals using documented methodologies that lead to verifiable results and conclusions. Strategy BA 1.1.2. Whenever feasible, consult with a qualified state agency personnel, scientific experts or team of experts to help identify and determine the best available scientific information and assess its applicability to the relevant critical areas.
Policy BA 1.2. Adopt and enforce ordinances that require the use of best available science in the management of critical areas including natural wetlands, critical aquifer recharge areas for potable water, fish and wildlife habitats , frequently flooded areas and geological hazardous areas.
Strategy BA 1.2.1. Ensure that the best available science is being included in policies and regulations, by considering the “characteristics” of a valid scientific process and common sources of scientific information [see Chapter 365-195-905(5) WAC]. In the context of critical areas protection, a valid scientific process is one that produces reliable information useful in understanding the consequences of a local government’s regulatory decisions.
The City of Prosser (City) recognizes the intent of the voters and the legislature of the State of Washington in adopting the “Shoreline Management Act of 1971” (SMA) and adopts by reference the finding that the shorelines of the state are among the most valuable and fragile of its natural resources and that there is great concern throughout the state relating to their utilization, protection, restoration, and preservation. In addition, it finds that ever increasing pressures of additional uses are being placed on the shorelines necessitating increased coordination in the management and development of the shorelines of the state.
The SMA’s paramount objectives are to protect and restore the valuable natural resources that shorelines represent and to plan for and foster all “reasonable and appropriate uses” that are dependent upon a waterfront location or that offer opportunities for the public to enjoy the state’s shorelines. With this clear mandate, the provisions of the SMA established a planning and regulatory program which is initiated at the local level under state guidance.
This cooperative effort balances local and state-wide interests in the management and development of shoreline areas. Local governments are required to plan for shoreline development by developing local shoreline master programs (SMPs). They are also required to regulate such development through a shoreline permit system for substantial development projects.
Local government actions are monitored by the State of Washington Department of Ecology (Ecology), which approves new or amended SMPs, reviews substantial development permits, and approves conditional use permits and variances. The master program is essentially a shoreline comprehensive plan and regulations with a distinct orientation toward shoreline areas and customized to local circumstances. Collectively, the local master programs comprise the State Shoreline Master Program.
The City developed and adopted its first shoreline master program with the help of a citizen advisory group in 1973. The Master Program was subsequently amended several times during the intervening years. For the current comprehensive update, the City has conducted a comprehensive inventory of the natural characteristics, present land uses, and patterns of ownership along the City’s shoreline that provides a substantial information base for understanding ecological functions and other considerations for the update of this Master Program. The City, with the involvement of its local citizens, agencies, and interested parties, has developed this Shoreline Master Program to serve as both a planning guide and resource for specific regulations pertaining to development and use of the shorelines in City of Prosser. Included is a description of the goals, objectives, policies, environments designations, use regulations, and provisions for administration including variances and conditional uses.
Prosser shorelines consist of the Yakima River shoreline. This includes floodways, land within 200 feet of the ordinary high water mark (OHWM) of the waterways; floodplains up to 200 feet from the floodway edge; and associated wetlands. The City has chosen to include the minimum shoreline jurisdiction required according to the State law (RCW 90.58.030).
Goal SH1 Shoreline Use Element. Ensure appropriate conservation and development of the City of Prosser’s shorelines by allowing those uses which are water-dependent, as well as other development which provides an opportunity for a substantial number of people to enjoy the shorelines. This should be done in a manner which will achieve an orderly balance of shoreline uses that improves the quality of the environment.
Policy SH 1.1 Ensure that all uses and developments do not result in a net loss of shoreline ecological functions.
Policy SH 1.2 Accommodate water-dependent and associated water-related uses that are the highest priority for shorelines unless protection of the existing natural resource values of such areas precludes such uses.
Policy SH 1.3 Accommodate water-related and water-enjoyment uses that are compatible with ecological protection and restoration objectives are the second highest priority.
Policy SH1.4 Limit non-water-oriented uses to those locations where access to the water is not practical or where the non-water-oriented use contributes to the objectives of the SMA in providing ecological restoration and public access.
Policy SH-1.5 Reserve the shoreline areas for uses which allow optimal uses for future generations by recognition and of potential long-term benefits to the public, and discouragement of short term gain or convenience.
Policy SH 1.6 Provide site development performance standards and other appropriate criteria to developers indicating acceptable standards to be achieved.
Policy SH 1.7 Allow multiple uses of shoreline areas where integration of compatible uses or activities is feasible.
Policy SH 1.9 Allow uses, on a specified interim basis, which are not shoreline related, if not permanent and if not requiring permanent modifications of natural shorelines.
Policy SH 1.10 Respect private property owner’s rights when drafting development regulations for use of the shorelines.
Goal SH 2 Shoreline Economic Development Element. Give priority to those industrial, commercial, and recreational developments that are particularly dependent on their location on the City of Prosser’s shoreline. Encourage development that will provide the public with an opportunity to enjoy the shorelines. No net loss of ecological function is envisioned in the implementation of this goal.
Policy SH 2.1. Minimize the adverse effects of new commercial, industrial, and recreational development upon the physical environment and natural processes, through careful siting and design.
Policy SH 2.2 Locate commercial and industrial development as infill in areas already developed as a first priority, so long as such areas have not reached their functional capacity.
Policy SH 2.3. Locate new commercial, industrial, and recreational activities in areas with existing public services as a second priority.
Policy SH 2.4 Provide for effective flood protection for the City of Prosser.
Goal SH 3 Shoreline Economic Development Element Develop safe, convenient, and diversified shoreline circulation systems to assure efficient movement of goods and people with minimum disruptions to the shoreline environment and minimum conflict between the different users. Policy SH 3.1 Locate and design major circulation systems well away from the shoreline, except for necessary crossings, so that natural shorelines remain substantially unmodified.
Policy SH 3.2 Encourage existing corridors for transportation facilities along shorelines to better accommodate public access to the shoreline and provide safe overcrossings to shoreline public access facilities.
Policy SH 3.3 Encourage joint uses of any necessary roads.
Policy SH 3.4 Encourage alternate modes of transportation such as pedestrian and bicycle to the shoreline.
Goal SH 4 Restoration and Conservation Element. Assure protection, preservation, and restoration of City of Prosser’s, fragile and scenic nonrenewable resources, while encouraging the best management practices to assure no net loss of shoreline ecological functions.
Policy SH 4.1 Existing natural resources should be conserved through regulatory and non-regulatory means that may include:
Implementation of the Comprehensive Plan, local development regulations, and state, tribal, and federal programs;
Regulation of development within the shoreline jurisdiction;
Ecologically sound design;
Restoration programs; and
Policy SH 4.2 Provide for the use of shoreline and floodplain-related resources without harming other natural systems or the overall quality of the natural environment.
Policy SH 4.3 Effectively manage natural features and resources as well as scenic vistas, parkways, and habitats of rare or endangered species.
Policy SH 4.4 Preserve the scenic and aesthetic qualities of shorelines, floodplains, and vistas.
Policy SH 4.5 Provide for restoration of degraded ecological functions through appropriate regulations including emphasis on non-water-dependent uses and as part of publicly-funded facilities.
Goal SH 5 Public Access Element. Ensure safe, convenient, and diversified access for the public to the publicly-owned shorelines of the City of Prosser and assure that the intrusions created by public access will recognize the rights of private property owners, and will not adversely affect fragile natural areas.
Policy SH 5.1 Public access should be provided consistent with the existing character of the shoreline and with consideration of opportunities and constraints for physical and visual access, as well as consideration of ecological functions and public safety.
Policy SH 5.2 Public access to and along the water’s edge should be available throughout publicly owned shoreline areas, although direct physical access to the water’s edge may be restricted to protect shoreline ecological values.
Policy SH 5.3 Future developments and redevelopments shall not adversely affect existing public access, and should provide new opportunities for the public to reach, touch, and enjoy the water’s edge.
Policy SH 5.4 Locate, design, develop and maintain public access in a manner that enhances the natural environment.
Policy SH 5.5 Purchase, or otherwise make available to the public, shoreline properties if their value for public use merits such action.
Policy SH 5.6. Existing highway and railroad corridors along shorelines should better accommodate public access to the shoreline and provide safe overcrossings to shoreline public access facilities.
Policy SH 5.7 Coordinate shoreline public access with local, state, and federal agencies.
Policy SH 5.8 Respect and protect the enjoyment of private rights in shoreline property when considering public access development.
Goal SH 6 Goal: Recreational Element. Provide additional opportunities for diverse forms of public recreation and improvement of present facilities. Policy SH 6.1 Identify, obtain, preserve, and protect areas with high values for recreation.
Poli y SH 6.2 Consider allowing recreational uses as part of private development where compatible with other uses and activities.
Policy SH 6.3 Provide a balanced choice of recreational opportunities, including those requirements of the elderly and the physically challenged.
Policy SH 6.4 Cultivate innovative and cooperative techniques among public agencies and private persons or groups which increase and diversify recreation opportunities.
Policy SH 6.5 Allow compatible recreational uses including bicycle and foot paths in transportation and utility corridors where feasible.
Policy SH 6.6 Locate, design, and operate recreation facilities in a manner consistent with the purpose of the environment designation in which they are located so that no net loss of shoreline ecological functions or ecosystem-wide processes result.
Policy SH 7.6 Coordinate with local, state, and federal agencies so that shoreline recreational developments are consistent with the City and Regional Parks Recreation, Open Space and Trails Plan.
Goal SH 7 Historical/Cultural Element. Protect, preserve, and encourage restoration of those sites and areas on the shoreline which have significant historical, cultural, educational, or scientific value.
Policy SH 7.1 Identify historic, cultural, and archaeological resources within the shoreline in cooperation with federal, state, local, and tribal agencies.
Policy SH 7.2 Plan for preservation of significant historic, scientific, and educational areas of the shoreline while providing for public use and enjoyment of such areas.
Policy SH 7.3 Preserve for the public benefit, with opportunity for appropriate public utilization, significant historic, scientific, and educational areas of the shoreline.
Policy SH 7.4 Ensure that the review and construction of development permits includes professional assessment of historic, cultural, and archaeological resources and that such resources are preserved or conserved in compliance with applicable laws.
Goal SH 8 Flood Hazard Element. To minimize flood hazards to human life and to property while enhancing the ecological processes of the shoreline. Policy SH 8.1 Manage flood protection through implementation of the City’s Comprehensive Plan, stormwater regulations, and the regional flood hazard control plans for the Yakima River.
Policy SH 8.2 Protect existing development and restore floodplain and channel migration functions to the extent feasible.
Policy SH 8.3 Integrate bioengineering and/or soft engineering approaches where feasible into local and regional flood control measures, infrastructure, and related capital improvement projects.
Policy SH 8.4 Prohibit development within the floodplains associated with the City’s shorelines that would individually or cumulatively result in an increase to the risk of flood damage while preserving the rights of individual property owners.
Policy SH 8.5 Support measures to increase the natural functions of floodplains including flood storage, off-channel habitat, associated wetlands, and buffers of native vegetation.
Natural Resource Areas
Goal NR 1: To support the conservation designated Natural Resource areas in the Prosser area. Policy NR 1.1. Recognize that natural resources, defined as agricultural lands, or mineral resource lands, are essential for the long term viability of the City of Prosser.
Strategy NR 1.1.1. Support the designation of natural resource areas in the County comprehensive plan and avoid actions that may assist in converting agricultural lands to non-agricultural related uses.
Strategy NR 1.1.2. Require, if the City annexes areas with (or adjacent) to designated natural areas, that all plats, short plats, development permits, and building permits issued for development activities on, or within five hundred feet of, lands designated as agricultural lands, or mineral resource lands, contain a notice that the subject property is within or near designated agricultural lands, or mineral resource lands on which a variety of commercial activities may occur that are not compatible with residential development.
Storm and Surface Water management
Goal SW 1. To manage storm and surface water flows in a manner that reduces potential contamination to aquifers and surface water bodies. Policy SW 1.1. The City shall develop and implement a Stormwater Management Program (SWMP).
Strategy SW 1.1.1. Design the SWMP to reduce the discharge of any pollutants to the Maximum Extent Practicable (MEP), by applying All Known, Available, and Reasonable methods of prevention, control and Treatment (AKART) prior to discharge.
Strategy SW 1.1.2. Implement a public participation program as part of the SWMP.
Strategy SW 1.1.3. Detect and eliminate illicit discharges.
Strategy SW 1.1.4. Review development proposals to reduce discharges of pollutants from the development to the Maximum Extent Practicable (MEP), by applying All Known, Available, and Reasonable methods of prevention, control and Treatment (AKART) prior to discharge.
Figure 4: Map of Generalized Critical Areas
Background Land Use
Table 1: Existing Land Uses
In October of 2006, Dugan Planning Services conducted an inventory of existing land uses in the City of Prosser. 1,330 acres (55%) of the 2,429 acres that are on lots or parcels, excluding right of ways, of the city is undeveloped. Residential land uses comprise the largest type of developed area within the city; making up 16% (394 acres) of the total area of the city that is in lots or parcels.
Table 2: Existing Use compared to Planed Uses
Figure 5: Distribution of Existing Land Uses
The comprehensive map plan allocates much of the undeveloped area of the city to future uses as illustrated on Figure 5.
Figure 6: Existing Uses Compared to Planning and Zoning
Figure 7: Map of Existing Land Uses
Table 3: Prosser Decennial Population
Figure 8: Population Growth
The 1996 Comprehensive Plan included a complete analysis of the demographic characteristics of the community. The data presented in that analysis was updated with a report entitled City of Prosser Census, Summary File 3. This analysis and update is incorporated herein as background information for the housing and land use elements.
Table 4: Population Growth 1991-2006
While the average decennial population increase between 1940 and 2000 was 21% 19%, the most rapid period of growth occurred between 1940 and 1950 when the population grew by more than 50% (adding 914 people) and between 1970 and 1980 when the population grew by over 40% (adding 1,213).
Population Forecasts and Capacity to Accommodate the GMA Population Allocation
Under the Growth Management Act, each city is required to accommodate its share of anticipated population growth in its county, as determined by the following process. The State Office of Financial Management (OFM) forecasts statewide growth. OFM then forecasts each county’s share of this statewide growth. Each county then allocates, consistent with its adopted county wide planning policies, this share of state growth to each city and the unincorporated area of the county.
In 2002, new population allocations to each city were made through this process for the year 2025. Prosser was allocated by Benton County a population growth of 1,915 peoplebetween 2000 and 2025. This growth represents an annual growth rate of 1.2% per year. The low forecast prepared for the 2003 plan amendment (described below) runs slightly below a forecast based on this GMA allocation (the GMA allocation is 6,306 in 2020).
Table 5: City of Prosser Population Capacity
Table 6 above estimates the amount of land available for residential uses designated in the plan to determine whether the plan can accommodate this allocation. As noted, the population allocation can be accommodated within the designated residential area of the plan.
However, this calculation is just part of the overall picture since other factors should be taken into account to determine the plan’s capacity to accommodate population growth. The Countywide Planning policies adds other factors to this type of analysis to determine the size of the urban growth area, including:
An additional 25% factor to accommodate streets, open space and other public facilities that may be needed to serve new developments. (Infrastructure factor).
An assumption that only 70% of the area will be built-out due to the plans ofindividual property owners. (Property owner plans).
An additional 30% market factor to ensure ample supply of land to avoid artificially limiting land supply in a manner that would drive up land costs. (Market Factor).
Applying these factors to the analysis would require an additional 117 acres to include accommodate these factors for 621 additional units (calculated at 4.5 units per gross acre).1 Adding these acres to the 138 acres needed for the units themselves (at 4.5 units per acre), 255 acres would be needed to accommodate the population allocation. Comparing this to the total acres available from Table 5 (168 acres) there is a deficit of 87 acres within the city limits. Ample area exists in the urban reserve (which has about 500 acres) and the unincorporated portion of the UGA (which has about 1,900 acres excluding existing rights of way).2
In addition, as more people may be added, room will be needed to accommodate additional commercial, employment and public services, as well as areas for open-space uses. The Countywide policy incorporates a formula which includes all uses that may be needed to accommodate the population allocation as a means of determining the appropriate size of the City’s urban growth area.
If the allocation does fall short of providing space for the additional population, additional residential area can be added either by further planning a zoning of the urban reserve area or by annexing more area. Policy Goal MN 1 provides for monitoring future development trends in order to take any corrective action that may be needed if the allocation appears to be falling short due to low yields on residential areas. Currently this monitoring would show that population growth is falling behind both the 2003 forecasts and the GMA allocation, as illustrated on the line with the triangular symbols on the graph below. Currently, actual growth in the City as of 2006 is running below the low forecast.
In the 2003 amendment to the comprehensive plan, a population forecast was prepared. High, medium and low population estimates were projected for the years 2005, 2010, 2015 and 2020, which are shown on Table 6.
Table 6: 2003 population Forecasts
The high population estimates are based upon an annual 3.5% growth rate from 2003. The medium population estimates are based upon an annual 2.3% growth rate. The low population estimates are based upon an annual 1.1% annual growth rate. The land-use-demand calculations are based on the medium population growth rate. Actual population growth is lagging behind the 2003 forecasts. The city’s official 2005 population of 5,045is below the amount that was forecasted for that year in the 2003 low forecast.
Figure 9: Forecasted Population Growth
Hydrogeology The Prosser Urban Growth Area, situated along the Yakima River, lies about 10 miles west of the region known as the Pasco Basin, and is located on the Columbia Plateau. The Columbia Plateau is underlain by a series of basalt flows and sedimentary interbeds commonly referred to as the Columbia River Basalt Group. These Miocene-age flows erupted between 6 and 17 million years ago. The flows have formed a generally horizontal, layered sequence, which have an estimated thickness of 14,000 feet at the plateau’s low point near Pasco. In order of decreasing age, the upper three major formations of the Columbia River Basalt Group of relevance to this plan include the Grande Ronde, Wanapum, and Saddle Mountain Basalts. These three formations comprise the Yakima Basalt Subgroup.
The overburden of the Columbia Plateau includes consolidated to unconsolidated deposits of fluvial, lacustrine, and volcanic origin. Prosser lies upon alluvium, which is primarily gravels and boulders. The alluvial thickness at the city wells ranges from about 30 to 65 feet, and the land elevation ranges from about 650 to 700 feet.
The Vantage sedimentary interbed is typically found between the Wanapum and Grande Ronde Basalts, and the Mabton sedimentary interbed generally separates the Saddle Mountain and Wanapum Basalts. Little information on the thickness of the Vantage interbed is available for Prosser, however the top of the Grande Ronde Basalts is estimated to be at an elevation of 1,000 feet. Regional studies indicate that the Saddle Mountain Basalts is up to about 900 feet thick in the vicinity. The top of the Mabton interbed is located at about elevation –204 feet at Well No. 5, where its thickness is about 125 feet. It was encountered at about elevation –219 at Well No. 6, where its thickness is about 42 feet. The top of the Wanapum Basalt is at elevations –329 feet and –261 feet at Wells Nos. 5 and 6 respectively, and is estimated to be about 800 feet thick.
The city maintains five water supply wells. The primary aquifer supplying the city wells consist of fractured and porous layers within the lower Saddle Mountain Basalts and the upper and middle Wanapum Basalts below the depth of 500 feet. Wells Nos. 2, 3, and 4 are 768, 599, and approximately 742 feet deep, respectively, and each draws water from the Saddle Mountain Basalts. Wells Nos. 5 and 6 are 1,264 and 1,465 feet deep, respectively, and both collect water from the Wanapum Basalts. Recharge to the aquifers is provided by lateral migration of groundwater and vertical infiltration of precipitation and irrigation water.
Environment/Critical Areas The Growth Management Act requires municipalities to protect the environment and enhance Washington’s high quality of life, including air and water quality and the availability of water. Cities are required to regulate and protect fish and wildlife habitats, wetlands, steep slopes, aquifer recharge areas, frequently flooded areas, and the shorelines of the Yakima River while providing access to natural resources and the water.
The Yakima River is a river of statewide significance, regulated by the city’s shoreline master program and critical area ordinance. The river is additionally an aquifer recharge area, a wildlife habitat area, contains wetlands, and is a frequently flooded area noted for periodic severe flooding during the winter and spring months. The 100-year flood levels are mapped on the FEMA Flood Insurance Rate Maps for the City of Prosser and Benton County. The Yakima River narrows near Prosser and is an especially high-quality riparian corridor and major habitat and nesting place for many species of indigenous and migratory birds. Habitat and species mapping is provided by the Department of Natural Resources and the Fish and Wildlife Services and should be utilized when identifying critical areas and considering mitigation of development proposals.