Steep slopes pose challenge for water, sewers and streets on northwest side of Forest Grove

COURTESY GRAPHIC - The Westside Planning Project on the northwest side of Forest Grove could add 2,054 homes over the next 35 years.The Forest Grove Planning Commission held a work session on the Westside Planning Project, which aims to prepare a plan for two areas at the north end of Forest Grove to be developed over the next 35 years, bringing a maximum of 2,054 housing units to the city.

This new 553-acre neighborhood will sprout at the city's northwestern border, near David Hill, Purdin and Thatcher roads.

The plan encompasses the design and costs of the major road system, sewer lines, stormwater system, water system and parks. Schools are a responsibility of the school district.

In developing a new area, the major roads are arterials, which are required to be at least one mile apart, and collector streets, which must be only a half-mile apart, as shown on the proposed street map (right).

A major challenge in the western part of this area is the topography. City streets are generally not allowed to slope with a steeper grade than 12 percent, possibly increasing to 15 percent if absolutely necessary. But the western part of this area has many spots where the terrain naturally slopes at a 25 percent grade.

The street map shows the major streets, as well as the parts (in yellow) where the slope exceeds a 12 percent grade.COURTESY GRAPHIC - This street map for the David Hill area shows places (yellow lines) where the terrain naturally slopes more than the 12 to 15 percent allowed for streets.

Also, the improvements on David Hill Road, west of Thatcher Road will provide a sidewalk on one side, as well as bike lanes and 32 feet for vehicle lanes. Normally, this collector street would be 40 feet, but in order to minimize the need to cut into hillsides, we believe a narrower street would be better.

On the street map, note that both road 7 and road 8 end without connecting to Thatcher Road and Purdin Road respectively. This is because in both cases the road must end at the Urban Growth Boundary and in both cases the land outside the boundary is designated Rural Reserves, which prohibits development. We suggested that an additional road might connect road 2 with David Hill.

The sewer, water, and stormwater systems follow the road system. Two challenges emerged with these systems. First, the topography for sewers would require either a line over the Rural Reserves east of Thatcher or filling about 800 feet of Thatcher where Thatcher traverses a ravine. We favor filling Thatcher, which also allows the use of the main sewer line along David Hill Road.

The city's water system is only sufficient to serve those areas below 440 feet of elevation, and the highest part of the David Hill area will exceed this. To provide an adequate supply of water for all the new areas, the city will need to build one or more new reservoirs, which will likely add a cost of about $5,000 per household at the time of construction.

The city's new parks plan calls for improvements to Thatcher Park and the establishment of a new park near Purdin Road.

Total costs of the infrastructure will be $47.6 million, including $30 million just for streets. The usual manner of paying for infrastructure is a System Development Charge — currently $22,600 per residence or $9.03 per square foot of floor space. Given the fact that the Westside areas have no infrastructure at the moment, we are thinking of charging $36,100 in the David Hill area and $34,700 in the Purdin area, or $14.43 per square foot (in today's dollars).

The new charges would be more than currently charged in North Plains ($27,600) or Beaverton ($31,000), but less than those proposed for the new South Hillsboro development of $44,100. We asked for comparisons with cities more like Forest Grove to give us an idea of the feasibility of raising the SDCs.

Since this plan is a legislative matter, the planning commission only recommends to the city council. We will be considering our recommendation when we hold a public hearing on this subject, most likely in April. The city council will hold its own public hearing on this plan after receiving our recommendation.

Always glad to answer inquiries at This email address is being protected from spambots. You need JavaScript enabled to view it..

Tom Beck writes a column on the activities of the Forest Grove Planning Commission, which he chairs.

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