Watershed Planning
Watershed Planning
This domain tests how Oklahoma identifies impaired waters, sets pollution budgets, and plans corrective actions across a watershed. It connects water quality standards, monitoring, the 303(d) impaired waters list, total maximum daily loads (TMDLs), and watershed-based plans. Oklahoma's water quality standards define designated beneficial uses and numeric or narrative criteria; DEQ applies them in permits and TMDL development, while OWRB has water planning and standards responsibilities. A watershed plan is not just a document: it should identify causes and sources, estimate load reductions, select best management practices (BMPs), estimate costs, set milestones, and include monitoring.
Core rules and concepts
- A TMDL is the maximum pollutant load a water body can receive and still meet standards. It is allocated among point sources (WLA), nonpoint sources (LA), and a margin of safety (MOS), often with future growth.
- Point-source loads are implemented through NPDES permits; nonpoint reductions rely on voluntary and funded practices.
- Watershed-based plans often use Clean Water Act section 319 funds and need measurable milestones and a monitoring plan.
- Source water protection focuses on preventing contamination of drinking water sources, not just treating it.
Worked example
A TMDL for a stream is 1,200 lb/day of sediment. The margin of safety is 10% and the wasteload allocation for point sources is 300 lb/day. MOS = 0.10 × 1,200 = 120 lb/day. Load allocation = 1,200 − 120 − 300 = 780 lb/day. That 780 lb/day is spread across nonpoint sources in the watershed; it is not a single permit limit.
Traps
Treating a TMDL as self-implementing; confusing load (lb/day) with concentration (mg/L); assigning all reductions to point sources; ignoring seasonal variation; and writing a plan with no milestones or monitoring.