A Model for Evaluating the Impacts of Spatial and Temporal Land Use Changes on Water Quality at Watershed Scale Jae-Pil Cho and Saied Mostaghimi 07/29/2003

Overview of presentation Introduction Model characteristics Model components Model application Summary & Future improvement

Introduction Effectiveness of BMPs varies both temporally and spatially Ideal NPS model for BMP evaluation Long-term, continuous-simulation model Distributed-parameter model Process-oriented model Objectives To develop a continuous, distributed, and process- oriented watershed scale model for assessing the effectiveness of temporally and spatially changing BMPs To demonstrate the model applicability

Model Characteristics

Conceptual Model Baseflow Interflow Root zone Interception Evapotranspiration Infiltration Percolation Overland flow Channel flow

Flowchart of the model Define soil layers Read main input Begin Simulation Initialize the model End Simulation Simulation Period Over ? Read weather data (1day) Yes Pesticide degradation Calculate daily changing Check rotation changes Calculate daily changing variables (ET,crop, soil,surface) No Runoff=0 ? No Read breakpoint data (get start time of rainfall) Yes Overland flow routing Infiltration Overland sediment routing Overland pesticide routing Channel flow routing Percolation Pesticide leaching Channel sediment routing Channel Pesticide routing Lumped Interflow and Baseflow Precipitation ? No Yes Multiple soil layers based on physical soil layers and rotation information such as pesticide application depth and tillage depth Soil Parameters Porosity, bulk density Effective hydraulic conductivity Rill and Interrill erodibility Crop Parameters Canopy cover and height Leaf Area Index(LAI) Root depth Ground surface parameters Random roughness Ridge height Residues(flat, buried, dead root) Runoff Rainfall 1-day User defined during rainfall time step Before rainfall time step During rainfall time step After runoff time step

Separate input files Blocks in main input Separate output files Output parameters Weather Break-point Main Initial Flag & General input Initial Cell Crop Tillage Pesticide Rotation Channel Soil Output Rotation Initial Input file structure for considering spatial and temporal land use changes Physical Data Temporal Data Spatial Data

Dynamic parameters Leaf Area Index (LAI) Canopy cover Canopy height Root depth Crop Surface Soil Water and Temperature stress Biomass  Above ground  Root Random roughness Ridge height Residues Flat residue Buried residue Dead root residue Porosity, B-Density Effective hydraulic conductivity Rill and Interrill erodibility Rainfall  Cu. amount  Kinematic E. Spatial and Temporal Land Use Changes Tillage  Type  App. date

Model Components

Hydrology & Sediment Hydrology Overland flow: Continuity and Manning’s equation Evapotranspiration: Ritchie’s method Infiltration: Green-Ampt infiltration for unsteady rainfall Percolation: WEPP approach Sediment (Based on WEPP) Rill detachment Interrill detachment Channel scour

Pesticide: application methods Surface and Foliage application User defined depth & linearly decreasing with depth Soil and foliage application Depth Pesticide Incorporation Pesticide Injection Pesticide Incorporation User defined depth & Uniform distribution Injection User defined depth & no mixing above this depth

Pesticide: Retention / degradation / transport Interaction between solution and soil phase Linear isotherm: instantaneous & reversible C s = K d X C w Degradation First-order kinetics: lumped dissipation parameter C d = C o e –k d Adjustment of dissipation rate based on soil temperature and soil moisture content Transport Runoff Leaching Plant uptake

Model Application

Nomini Creek Watershed

 Ground water dominant watershed(GWI=0.85)  Detail land use changes and pesticide application data ( )  Typical planting, harvesting, tillage, pesticide application date was decided  Simulation period: 01/01/ /31/1991  Cell size: 90m*90m (267 cells)  Pesticide PesticideSolubility (ppm) Half Life Soil(days) Half Life Foliage Washoff Fraction Koc (ml/g) Atrazine

Land use changes in QN2  55 fields and 36 different land use changes  Land use changes in field#6 ( ) Pesticide application Corn Small grain Soybean Corn Tillage application

Available Output Files  Flux  Surface to Root zone  Root to Intermediate zone  Outlet  Daily  Event  User defined cell  Vertical distribution  Time series  Dynamic soil, crop, surface parameters

Outlet output: Daily and monthly runoff Error QN2 (89’-91’) Error in total volume %

Outlet output: Daily and monthly pesticide load Daily Monthly

Outlet output: Event hydrograph 07/16/89 Storm event

User-defined cell output: - Vertical distribution of pesticide concentration 4/26/1989 (Application) 5/5/1989 8/5/1989 9/5/ /5/1989 6/5/1989

Conclusions & Future Improvement A model was developed for assessing the impacts of spatial and temporal land use changes on hydrology and water quality and applied to NC watershed Future improvement Model validation (Hydrology, sediment, pesticide) Distributed ground water modeling Linkage with MODFLOW and MT3DMS Pre- and post-processor

Expecting modeling system GIS Weather Data Surface/Unsaturated zone model Surface/Unsaturated zone model MODFLOW/MT3DMS Result DB Output Input DB Arc/View (ASCII) Pesticide, Crop, Soil Data Output Input -Weather -Rainfall Input Excel (VBA) Interface Data flow 1 2 Update input database Create weather and breakpoint rainfall input data 3 Create main input 4 Update result database Interface

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