High Rock Lake Nutrient Modeling Update Pam Behm - NC Division of Water Resources Environmental Management Commission Water Quality Committee Information Item May 2015

PURPOSE To provide an update on the status of the High Rock Lake nutrient modeling and information on the next steps in the process of developing a Nutrient Management Strategy for the lake. 2

OUTLINE Statutory Authority Description of Lake and Watershed Impairment Status Watershed Model Lake Model Connection to Nutrient Criteria Development Plan Next Steps 3

High Rock Lake Watershed Yadkin Neuse Cape Fear 4

Statutory Authority 5

SESSION LAW SECTION 12. Section 4 of S.L , as amended by Section 31 of S.L , reads as rewritten: 6

High Rock Lake Crane Creek Abbotts Creek Swearing Creek Second Creek Yadkin River Flat Swamp Creek Grants Creek South Yadkin River 7

(d) Chlorophyll-a % greater than 40 μg/l standard Town/Crane Creek Abbotts Creek Second Creek Flat Swamp Creek Yadkin/South Yadkin Rivers 8

Distribution of Chlorophyll-a Data Chlorophyll-a Concentration (ug/L) MainstemArms 9

Watershed Model Estimates what is happening on land that results in nutrient export to receiving water (i.e. High Rock Lake) Provides relative loading by source (agriculture, developed, point sources, etc.) 10

Watershed Model Results Spatial Distribution of Flow and Nutrient Loading to High Rock Lake 11

Sources of Loading

Sources of Loading

Nutrient Response Model Model Scenarios Determines nutrient load reductions that will achieve water quality standards Existing loading from all sources Lake Response Chl-a Lake Response Chl-a Reduced loading 14

Model Results Calibration Criteria ▫ Visual ▫ Statistical (e.g. relative error, coefficient of variation, correlation coefficient) YAD152C (mid-lake) Final Report: 15

Limiting Nutrient(s) Predicted by the model/supported by data Varies with time, space, impact of turbidity By location: Upper lake – more turbidity limitation Middle lake – frequent co-limitation by nitrogen and phosphorus during growing season Forebay – phosphorus is usually limiting, with some brief periods of nitrogen limitation 16

Model Results Final TAC meeting – held April 29 Final report on website: END of TOOL DEVELOPMENT (Step 1 in NMS Development Process Completed) 17

Nutrient Management Strategy Development Process Step 1: Build the tools Who: DWR and TAC What: Monitoring Modeling Step 2: Develop the strategy Who: DWR and Stakeholders What: Reduction targets Point and nonpoint strategies 18

Nutrient Management Strategy Next Steps Staff will begin scenario development – based on data/model performance Stakeholder process- delayed NCDP 19

Questions? Pam Behm