3.6 Impacts of Future Growth
Water Quantity and Quality
Land use change impacts downstream water quality by increasing the volume of runoff and the concentration and load of nutrients and sediment transported to receiving waters. Table 8 illustrates how land use change such as the expected conversion of agricultural and vacant land to low- and medium-density residential could be expected to impact water quality in Schutz Lake. The table also illustrates the impact of a regulatory program managing these impacts.
Ultimate development in this case is defined as the conversion of all agricultural lands and one-half of the upland forested area outside the regional park that remains undeveloped in the 2020 local government land use plans. This conversion may take place by 2030 or require significantly more time; but it is assumed that at some point in the future these conversions will occur. More detail regarding this modeling can be found in Technical Appendix A.
Table 8 contrasts three loading reduction scenarios. Scenarios 1 and 2 contrast the expected results if there were no regulatory program to the results under the existing regulatory program. The HHPLS assumed that there would be no load increase from future development; the third scenario indicates that even with a regulatory program that strictly prohibits any new phosphorus loading, additional reductions would be necessary to achieve the desired phosphorus concentration goal of 40 ?g/L.
|Scenario 1: No Regulatory Program|
|Predicted in-lake TP (?g/L)||52|
|P load decrease needed to achieve 40 ?g/L (lbs/year)||124|
|Scenario 2: Current Regulatory Program|
|Predicted in-lake TP (?g/L)||48||47|
|P load decrease needed to achieve 40 ?g/L (lbs/year)||70|
Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development (As assumed in HHPLS)
|Predicted in-lake TP (?g/L)||42|
|Additional P load decrease needed to achieve 40 ?g/L (lbs/year)||17|
While most of the upper Schutz Lake subwatershed outside the Carver Park Reserve has been impacted by development, the southern, upper subwatershed is yet only moderately developed. The area outside the park reserve faces varying threat levels from degradation as a result of development pressure, urbanization, and subsequent channelization of stream conveyances. Those impacts could exacerbate impacts already affecting natural resource integrity in the downstream, developed part of the subwatershed. Prior to the encroachment of additional development, the opportunity exists to create a connection between the upper and lower subwatershed to improve water quality, preserve natural conveyances, and facilitate the movement and proliferation of native species as well as enhance recreational opportunities.
The opportunity exists to conserve approximately 4700 feet of channel and 105 acres of adjoining wetland complexes and adjacent high priority uplands. This will improve the characteristics of the aquatic ecosystem and the water quality within the subwatershed as well as areas downstream. Key Conservation Areas and the corridor plan for this subwatershed are illustrated on Figure 19 of this document.