3.6 Impacts of Future Growth

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 9 illustrates how land use change such as the expected conversion of vacant land to low-density residential could be expected to ultimately impact water quality in Christmas 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 that remains undeveloped in the 2020 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.  Because the majority of the watershed is fully developed, there is little/no change in modeling results among the analyzed time period.

Table 9 contrasts three nutrient 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 in Table 9 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 15μg/L.

Table 9.  Christmas Lake modeled 2020 and ultimate development water quality and the total phosphorus loading reduction necessary to achieve in-lake total phosphorus concentration goals.

Christmas Lake TP Goal = 15 μg/L

2000

2020

Ultimate

Development

Scenario 1:  No Regulatory Program

Predicted in-lake TP (μg/L)

 

15

15

P load decrease needed to achieve 15 μg/L (lbs/year)

 

3

Scenario 2: Current Regulatory Program

 

 

Predicted in-lake TP (μg/L)

 15

15

P load decrease needed to achieve 15 μg/L (lbs/year)

 

3

Scenario 3: Regulatory Program That Prohibits A Net Increase in Loading from New Development (As assumed in HHPLS)

Predicted in-lake TP (μg/L)

 

15

Additional P load decrease needed to achieve 15 μg/L (lbs/year)

 

2