Chapter 2 - Urbanization of the Watershed

This chapter presents a brief description and analysis of present and projected population and land use within the Lake Minnetonka watershed. The projections are specifically designed to provide a framework for estimating water supply requirements of the growing population and the concomitant generation of wastewater, and the areal extent and probable location of lands devoted to urbanization.

Population growth in the Lake Minnetonka watershed is primarily due to the migration of the population from the Twin Cities area to outlying areas and communities. It is estimated that the population of the watershed was 45,000 in 1969 and that the population will increase to 81,000 by 1985 and to about 146,000 persons by the year 2000.

The area of the watershed occupied for urban uses is projected to increase from 22 square miles at present to 34 square miles in 1985 and to 49 square miles in the year 2000. This growth of urbanized area is expected to occur on the 73 square miles of the watershed which is not occupied by lakes and swamps, or otherwise unsuitable for urban use.

Data Sources

Although several agencies, local, state and federal, have dealt with land use and population in the Twin Cities Region and in the vicinity of the watershed, there has been no particular effort to identify growth on a specific watershed basis. A brief review of data sources and these earlier studies related to population, growth and urbanization in the Minnetonka watershed is provided as background for the analyses that follow.

Population

Federal Census. The census data for 1930, 1940, 1950, and 1960 was available at the start of the study. During the course of the study, the preliminary data for 1970 became available. Some of the census areas are municipalities, others are entire townships. Of the townships, most have a portion of the township outside the boundaries of the watershed, and an adjustment of the census data is required to obtain the population within the watershed.

Metropolitan Council. The Metropolitan Council of the Twin Cities Area (and its predecessor agencies) have published maps giving their estimate of the 1968 and 1985 population distributions. They also commissioned Metcalf and Eddy, Engineers and Planners, to prepare a study entitled "Sewerage and Water Planning Report" which was completed in 1968. Figure 4 of the Metcalf and Eddy Report is a map showing the Metropolitan Council's estimate of the population distribution for the entire metropolitan area in the year 2000.

These maps showing estimated future populations have been developed from information compiled for a highway traffic study. For the purposes of the traffic study it was more important to predict future population in small areas near the heart of the Twin cities than it was in small outlying areas.

Therefore, a study area in a downtown region might include only a few city blocks; whereas near Lake Minnetonka the study areas included entire census areas. Since the boundaries of the watershed include nearly all of two townships but only portions of other townships, it was necessary to estimate the portion of the predicted future population which will be within the watershed. This was done with the assistance of the staff of the Metropolitan Council.

Schoell and Madson. Scheell and Madson, engineers for the Southwest Sanitary Sewer District, found it necessary to estimate popUlations farther into the future than those estimates made by the Metropolitan Council. Scheell and Madson used those population forecasts which were available from the Metropolitan council, together with their own forecast of a "saturation population," to extend the forecast population to at least the year 2000.

Area Urbanized

An aerial photograph was used to determine the area urbanized in 1969. Proper interpretation of the aerial photograph was aided by visits to the watershed. The soUrces used for predicting urbanized areas in the years 1985 and 2000 are reviewed below.

Metropolitan Council. The Metropolitan Council has published a Development Guide for Sanitary Sewers which was adopted January 22, 1970 • This Development Guide indicates that the Metropolitan Council will attempt to foster "orderly urban growth" and minimize "leap-frog" development. The Development Guide also indicates that the sewerage program should be planned so that it does not encourage development in flood plains, airport clear zones, major aquifer recharge areas, and potential park sites. These guidelines were followed to predict future urban areas.

Wallace, McHarg, Roberts, and Todd. This firm has prepared, for the Metropolitan council, an "Ecological Study of the Twin Cities Metropolitan Area." The goal of this study was to determine what uses are especially suitable for a given parcel of land. Obviously some parcels will be suitable for several uses. For example, a parcel might be suitable for agriculture at the present time and urban development in the future. Other parcels were found by the authors of the study to be suitable for only one purpose. Predicted urban areas were confined to those areas deemed suitable for urban development in this report.

Projected Future Population

The projected future population used in this study is presented in Table 11-1 for individual communities and in graphic form for the entire watershed, as shown in Figure II-I.

Application of Populations

Care must be exercised in the application of the populations, especially those which are on the borders of the watershed. For example, the wastewater treatment plant at Maple Plain is within the watershed. The sewers bring all the wastewater from the community to the treatment plant. Therefore, for purposes of predicting flow or nutrient load, the entire community has been considered as being within the watershed even though some two thirds of the incorporated area is beyond the watershed boundary.

Plymouth presents a dual case. Sewers for Plymouth are presently under construction, and will drain east to the City of Minneapolis. For this reason, the population of Plymouth has been considered to lie completely outside the watershed for the purpose of predicting flow of wastewater and nutrient load in wastewater. on the other hand, for estimates of draft on the ground water resources for water supply, the population of Plymouth was included in the watershed population.

Community Populations

Table 11-1 shows population by community for the years 1930, 1940, 1950, 1960, 1970, 1985, and 2000. The populations for 1930, 1940, 1950, and 1960 were derived from the Federal census data. The population for 1970 was derived from preliminary census data. The populations for 1985 and 2000 are based on the forecasts prepared by the Me tropo li tan Council, with adjustments made for the portions of the communities which are outside of the Lake Minnetonka Watershed.

Dots are used to represent a unit of population of 100 or 200 persons on the maps published by the Metropolitan Council for population distribution in 1965, 1985, and 2000. The boundary of the watershed was drawn on these maps and the proportion of the population within the watershed was determined for each community. It was assumed that the 1965 distribution would apply to 1967 estimates and earlier counts of population. The distributions as determined from the "dot" maps for 1985 and 2000 were applied to the tabulated estimated populations for those years as published by Metcalf and Eddy for the Metropolitan Council in their "Sewerage and water Planning Report." Those 1985 and 2000 distributions were also applied to the data tabulated by 'Schoell & Madson in their work for the Southwest Sanitary Sewer District.

1. Twin Cities Metropolitan Planning Commission, population Distribution Twin cities Metropolitan Area - 1965.
2. Estimated Population - 1985 and Estimated Population - 2000 in "Sewerage and Water Planning Report" by Metcalf & Eddy November, 1968.
3. "Report on population and Sewage Flow Studies, Schoell & Madson, Inc. - Rieke, Carroll, Muller & Associates, Inc., August, 1969.
4. Report on Alternative Sewage Interceptor Routes North and West Lake Minnetonka Area TO Shorewood pumping Station," Schoell & Madson, Inc. - Rieke, Carroll, Muller & Associates, Inc., February, 1970.

Watershed Population

The total population of the watershed shown in Table 11-1 has been plotted on Figure II-I. The estimated growth from 1970 to 2000 represents a rate of about 4% per year. This is of the same order of magnitude as the growth rate from about 1935 to the present. It is less than the rate of growth experienced in the area between 1950 and 1960 (5.3% per year) and greater than the growth rate between 1930 and 1940 (2.9% per year).

Urbanized Area

Assumptions

Urbanized Area. It was assumed that most future land development would occur in areas within or adjacent to existing communities. It was also assumed that this development would not take place on land obtained by filling in existing lakes or marshes. These assumptions follow the general guidelines established by the Metropolitan Council's Development Guide for Sanitary Sewers. The lakes and marshes were indicated as being only suitable for conservation by the "Ecological Study."

The availability of sewers is just one of many factors which bear on the decision to develop a given parcel of land. Public water supplies and roads are other factors which enter the decision making process, and which 'the Metropolitan Council can influence. It has been assumed that the Metropolitan Council will use its influence in these and other fields to the same ends established in its Sanitary Sewers Plan and Program.

While Wallace, McHarg, Roberts, and Todd's Ecological Study was prepared for the Metropolitan Council, it does not necessarily reflect official council policy. However, those areas within the Lake Minnetonka Watershed denoted as being suited for only one purpose were generally small, with the exception of the "Conservation" classification. The areas deemed suitable only for Conservation included the lake surfaces, and these areas have been excluded from future development under the basic assumptions made above. The remaining single purpose areas
were small and also were excluded from land available for future development.

Population Densities. Due to many causes, there has developed a recent trend for constructing more apartment buildings and fewer single family houses. If this trend continues, the population densities of land developed in the future will be greater than land which has been developed to this time.

The population density around Lake Minnetonka in the late 1960's was approximately 1,800 people for each square mile, as determined by dividing the total population of the watershed by the total number of square miles of land which had been urbanized. If future urbanization occurs at this density, the projected watershed population of about 146,000 in the year 2000 would require just over 80 square miles of land.

The land within the watershed which will be ultimately available for urban development will be approximately the area of the watershed less the sum of the major parks, water surfaces, and marshes. That is, approximately 123 - (10 + 28 + 12) = 123 - 50 = 73 square miles. Therefore, development in the future must occur so as to increase the average density of population on urbanized-land within the watershed.

If the 73 square miles were occupied by a population of 146,000, the population density would be 2,000 persons per square mile. This is the equivalent of 3.1 persons per gross acre, or with 3.5 people per residence, one residential lot per acre. It has been assumed for purposes of this study that the future population growth will occur at 6,400 people per square mile, that is, about 10 people per acre, or 0.35 acres for an average home of 3.5 people. Allowing 20% for residential streets, the average lot size might be 0.28 acres - roughly 100 x 120 feet. Additional allocations of land were assumed to be as follows:

Commercial - 8.3 acres/1,000 people
Government and Institutional - 11.0 acres/1,000 people
Recreational - 12.5 acres/1,000 people
Utilities and Transport - 0.3 of all uses

The growth of population between 1969 and 2000 will be on the order of 146,000 - 45,000 = 101,000 people. Based on the assumptions above, this growth in population will require about 27 square miles. The overall population density in the future would then be:

146,000 people (22 + 27) sq. mi. = 2,980 people per square mile

Conclusions  

Maps showing the urbanized area within the watershed are included as Figures 11-2, 11-3, and 11-4. For the purposes of this study all urban uses have been classified together. Residential, commercial, or industrial properties are not distinguished on the maps.

Figure II-2 shows the 22 square miles which were urbanized in 1969 • Figure 11-3 shows the 34 square miles, (approximately 47 percent of the suitable land,) expected to be urbanized by 1985. Figure II-4 shows the 49 square miles (approximately 68 percent of the sui table land) expected to be urbanized by the year 2000.