Salinity TMDL Development and Modeling in the Otter Creek Watershed. Erik Makus DEQ Hydrologist June 6, 2013

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1 Salinity TMDL Development and Modeling in the Otter Creek Watershed 1 Erik Makus DEQ Hydrologist June 6, 2013

2 Outline for Today: Otter Creek and the Tongue River Previous salinity modeling efforts Existing Data Loading Simulation Program in C++ (LSPC) Modeling Salinity and SAR Scenario Development 2

3 3 Otter Creek watershed 707 square miles Spans three counties: Powder River 95% Rosebud 2.5% Big Horn 2.5% Elevations range from approx. 2,900 ft. to 4,425 ft. Mean annual flow in Otter Creek is about 4.5 cfs

4 Tongue River watershed 5,400 square miles Spans 2 states, 6 counties, and 2 Indian reservations. Tongue River Reservoir: 79,000 ac-ft. Mean annual flow in the Tongue River is about 390 cfs (near Birney, MT) Upper Tongue primarily snowmelt driven (Lower is 4 regulated by the reservoir).

5 Otter Creek and the Tongue River 5 Otter Creek salt load affects downstream 7% users in the Tongue 6% Otter Creek flow 5% makes up about 0.5% 4% of Tongue River flow 3% during summer 2% EC in Otter Creek 1% averages about 4x the 0% EC in Tongue River OC flow/tr flow (%) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

6 Previous modeling efforts EPA in 2007 Two separate watershed models plus a reservoir model to simulate the Tongue River Reservoir Looked at salinity, SAR, and nutrients. Tremendous amount of data collection for this effort. This effort is the basis for our future Tongue River modeling work. 6

7 Previous modeling efforts Modeling the Tongue River Watershed with LSPC and CE-QUAL-W2 (two documents - report and appendix) Water Quality Assessment for the Tongue River Watershed, Montana (two documents report and appendix). 7

8 Existing Data for Salinity Modeling Discharge (Flow) 8 Electrical Conductivity (EC) Agriculture Drinking Water Sodium Adsorption Ratio (SAR)

9 Existing Flow Data USGS Station Otter Creek at Ashland MT Agriculture Drinking Water 9

10 Salinity and Sodium Adsorption Ratio (SAR) Salinity is a measure of how much dissolved salt is in the water Can be measured several different ways, but the simplest is to measure as conductance either electrical conductivity (EC) or specific conductance (SC) All natural water is saline; however, too much can cause problems to things that use it (plants, aquatic life, livestock, humans) 10

11 11 Salinity and Sodium Adsorption Ratio (SAR)

12 12 Salinity and Sodium Adsorption Ratio (SAR)

13 13 Salinity and Sodium Adsorption Ratio (SAR)

14 14 Salinity and Sodium Adsorption Ratio (SAR)

15 Salinity and Sodium Adsorption Ratio (SAR) Sodium Adsorption Ratio (SAR) is a measure of the suitability of water for irrigation. A high SAR indicates the water is less suitable for irrigation. SAR is calculated using a ratio using calcium, magnesium, and sodium. SAR can be directly Agriculture measured in the field, or estimated from regression equations (USGS data). Drinking Water 15

16 Salinity and Sodium Adsorption Ratio (SAR) Agriculture Drinking Water 16

17 LSPC Loading Simulation Program in C++ A hydrology model that includes sediment and general water quality constituents, and a simplified stream fate and transport model Developed for EPA by Tetra Tech, based on the HSPF model (re-coded and updated) In the EPA TMDL Modeling Toolbox Runs on an hourly time step Uses energy balance for hydrology 17

18 SAR Modeling in LSPC LSPC models major cations using the general water quality module. So we model calcium (Ca 2+ ), magnesium (Mg 2+ ), and sodium (Na + ) Can then calculate SAR: 18

19 Salinity Modeling in LSPC LSPC does not specifically model salinity, but again, we are modeling calcium, magnesium, and sodium with the general water quality module. Major cations in water (Na, Ca, Mg, K, other metals, etc.) Use observed relationship between cation totals and salinity. 19

20 20 Salinity Modeling in LSPC

21 21 Salinity Modeling in LSPC

22 22 Salinity Modeling in LSPC

23 23 Salinity Modeling in LSPC

24 Pathways for water interaction Surface Runoff (Overland Flow) Interflow (soil-zone flow) Groundwater Flow 24

25 How can LSPC help us? Calibrate model to existing data from 1988 to 2010 (23 years). Determine existing load and compare to standards (EC/SAR). Make total maximum daily load determinations based on standards. Run various scenarios to see how the model responds to changing land use/management. 25

26 Modeling Scenarios Existing Scenario No Agriculture (Irrigation/Grazing) Scenario Potential Scenarios (Mine, CBM, etc.) 26

27 Summary TMDL goal: protect water quality (salinity and SAR) in the Otter Creek/Tongue River watersheds. 27 Modeling objective: identify relative source contributions of salinity (salts) under varying scenarios. Erik Makus

28 28 Erik Makus