Modeling flow and water quality in reservoir and river reaches of the Mahoning River Basin, Ohio

First posted February 27, 2023 For additional information, contact: Director, Oregon Water Science CenterU.S. Geological Survey601 SW 2nd Avenue, Suite 1950Portland, OR 97204 The U.S. Army Corps of Engineers (USACE) is considering changes to the management water surface elevation in four lakes Mahoning River Basin. These would affect timing and amounts released could quality those releases. To provide information on possible water-quality effects from these operational changes, flow models were constructed for Berlin Lake, Lake Milton, Michael J Kirwan Reservoir, Mosquito Creek Creek, dams downstream Lowellville, Ohio.The calibrated two calendar years each, with model selected depending availability data. Models developed CE-QUAL-W2 version 4.2 (Wells, S.A., 2020, CE-QUAL-W2—A two-dimensional, laterally averaged, hydrodynamic [version 4.2]: Portland State University, variously paged), a averaged model. Modeled constituents included flow, velocity, ice cover, temperature, total dissolved solids (TDS), sulfate, chloride, inorganic suspended sediment, nitrate, ammonia, Kjeldahl nitrogen, orthophosphate, phosphorus, particulate organic matter, algae, oxygen. Iron was lake models, but not river.A whole-basin model, river used run scenarios examine altered elevations lakes, outflows, River. initial year 2013 hydrology measured or typical quality, designated as scenario 0. flows close 20-year median flow. Four based reservoir operations (RES-SIM) provided by USACE. Scenario 1 RES-SIM base case, 2 kept higher summer, 3 allowed 25 percent summer flood storage extend guide curve, 4 more flexibility removing any minimum requirements. changed received lakes. Significant findings this study include following:In (Berlin Lakes), development grids using recent bathymetric surveys suggests that sedimentation has occurred since they constructed, altering volume-elevation curves.Tests parameter sensitivity showed modeled TDS, oxygen relatively insensitive values. chlorophyll a, measure algal concentration, most sensitive values; nitrate phosphorus concentrations affected few parameters tested. As group, results values compared model.Data gaps identified inflows, both quantity be filled through future sampling programs. Ample data available within waterbodies calibration.The simulated general spatial temporal patterns nutrients, River.From late spring autumn (2006, 2013, 2017–19 lake), all thermal stratification periods anoxia bottom waters. Stratification stable Reservoir least Lake. interrupted high-flow inputs moving lakes.The predicted release ammonia iron during anoxic hypolimnions.Concentrations increased down end modeled. greater than upstream releases.Chloride sulfate underpredicted River, suggesting presence unreported chloride river, at modeled.Model highest April mid-December period, 1–3. Model autumn, 3, satisfy requirements, other had lower elevation.As 1–3 largely similar because releases still met targets.Modeling removal targets, mid-September held November drawn prepare winter flood-risk management.In scenarios, outflows generally seasonal cycles though some differences predicted. instance, Milton hypolimnion period low inflows dam. It minimized maintaining pulses lake.Compared minor which maintained shifted source among largest between Leavittsburg Lowellville 4. led correspondingly case 1. Conversely, overall TDS nutrients portion time year.