R.K. Johnston, P.F. Wang, E.C. Loy, A.C. Blake, K.E. Richter, M.C. Brand, C.E. Kyburg, B.E. Skahill, C.W. May, V. Cullinan, W. Choi, V.S. Whitney, D.E. Leisle, and B. Beckwith

Uncertainty Analysis (Future Conditions)

The expansive growth buildout scenario was used to simulate future conditions to evaluate the effect of changing landuse on the water quality of Northern Dyes Inlet. This was accomplished by re-programming the watershed model HSPF with the projected changes in LULC to generate future flow conditions, recalculating the FC concentrations assigned to the streams and stormwater drainage basins in watershed based on the expansive buildout scenario, and then, simulating the future loading conditions with CH3D-FC for the May 2004 storm event. This assumes that the modeling system developed to represent present conditions is also applicable to future expansive buildout and that the relationships between LULC and modeled flow and LULC and predicted FC concentrations are still valid.

Buffer Conditions. The %CF in the 100 m buffer along streams was set to:

• Same – Future expansive buildout with the same %CF in the 100 m buffer as current conditions (S18);
• Reduced – Future expansive buildout with the %CF in the 100 m buffer reduced in proportion to the increase in TIA for the watershed (S19); and
• Full – Future expansive buildout with the %CF in the 100 m buffer set to 100% (S20).

Summary of present and future conditions for FC loading concentrations in watersheds in Northern Dyes Inlet

Summary of present and future flow conditions for watersheds in Northern Dyes Inlet

Future Simulation Results

S18: Simulate future conditions in Northern Dyes Inlet assuming expansive buildout and same level of CF buffer around streams

May 2004 storm event with future expansive buildout for flow and geomean FC concentration for watersheds in Northern Dyes Inlet (remaining watersheds same as base simulation), with same buffer as present conditions, and no wind.
Open animation of S18 simulation

S19: Simulate future conditions in Northern Dyes Inlet assuming expansive buildout and reduced CF buffer around streams

May 2005 simulation with future expansive buildout for flow and geomean FC concentration for watersheds in Northern Dyes Inlet (remaining watersheds same as base simulation), with reduced buffer, and no wind.
Open animation of S19 simulation

S20: Simulate future conditions in Northern Dyes Inlet assuming expansive buildout and full CF buffer around streams

May 2005 simulation with future expansive buildout for flow and geomean FC concentration for watersheds in Northern Dyes Inlet (remaining watersheds same as base simulation), with full buffer, and no wind.
Open animation of S20 simulation

Open animation of all future simulations

Supporting information: Download zip file of all HSPF files used to model future flow conditions: FutureModelingfiles.zip