With over 60% of its Oak Ridges Moraine lands designated as Settlement Area, Aurora’s planning decisions are where the rules governing growth at the ORM's edge are most frequently tested. In the East Holland River subwatershed, stormwater, grading, and servicing choices affect ORM headwaters and recharge features that feed local tributaries, including the Aurora Branch, before flowing north toward Lake Simcoe. The main risks are boundary and interface pressures, redevelopment and intensification spillover, and piecemeal approvals that can incrementally narrow Natural Linkage function and shift drainage patterns over time.