South East Regional Groundwater Flow Model- LEACHM Recharge Model

LEACHM Recharge Model produced as a result of the GOYDER INSTITUTE FOR WATER RESEARCH Project No.E.2.6.

The LEACHM model was used to create the recharge input files for the regional groundwater flow model developed as part of the same project.

LEACHM is a one-dimensional soil water and chemical fate and transport model (Hutson, 2003). Water flow is described either by a capacity (tipping-bucket) model or by a mechanistic (Darcy-based Richard’s) model. The mechanistic model was used in this work. It was used in a previous project to assess the risk of nitrogen and pesticide contamination in the Lower South East (Fleming and Hutson, 2014).

The GIS-linked version of the LEACHM model (LEACHG) aims to assess regional behaviour. The stand-alone LEACHM input data file consists of sections describing the simulation period, profile geometry and boundary conditions, soil, vegetation, chemical properties, irrigation and chemical management and weather. In LEACHG, each of these data components vary spatially, defined by GIS rasters based on state soil and land use maps, along with spatially interpolated weather data. In addition, features such as water table depth and land surface slope class etc. may also be applied to the model in GIS format. In LEACHG, each of the data file components are selected from a library of input data files linked to raster ID values. For example, if a land use raster cell has an ID of 23, then LEACHG will read data from a library file named Crops.023. Initially, the model reads all relevant rasters, identifies unique combinations of soil, land use and weather, and performs a single simulation of each combination for the defined time period. A complete set of LEACHM output files are generated for each simulation, identified by the raster ID values that are used to name the files. Post-processing generates rasters of any desired output variable, such as drainage from the soil profile, actual evapotranspiration or irrigation applications, produces summaries of water mass balance components both in terms of water depths and volumes, and generates input data files for the groundwater model MODFLOW.

The LEACHM code is written in the FORTRAN language. The code is continually improved and adapted to the requirements of specific projects and post-processing requirements; contact Dr John Hutson ([e-mail]). The time period of the LEACHM model simulations can be extended, however this requires modifying the input data files and obtaining or generating the required climate and land use datasets.

All datasets used in the model development are stored with the model.

Location: The model domain includes the Lower Limestone Coast Prescribed Wells Area in the Lower South East of SA (South Australia), and part of the Border Designated Area, and the encompassing groundwater flow system

LEACHM补给模型是由戈德水研究所（GOYDER INSTITUTE FOR WATER RESEARCH）E.2.6号项目研发的成果。
LEACHM模型被用于为同一项目中开发的区域地下水流模型生成补给输入文件。
LEACHM是一款一维土壤水与化学归趋及运移模型（Hutson, 2003），其水流过程可通过容水量（倾翻桶）模型或基于达西定律的理查兹机理模型进行描述。本次研究采用了机理模型。此前该模型曾被用于评估南东南部下南东地区的氮与农药污染风险（Fleming and Hutson, 2014）。
带有地理信息系统（GIS）关联功能的LEACHM模型版本（LEACHG）旨在评估区域尺度水文行为。独立版LEACHM的输入数据文件包含多个章节，分别描述模拟时段、剖面几何与边界条件、土壤、植被、化学属性、灌溉与化学管理措施以及气象数据。在LEACHG中，上述各数据组分均具备空间变异性，其定义基于州级土壤与土地利用地图生成的GIS栅格，以及空间插值得到的气象数据。此外，地下水位埋深、地表坡度分级等特征也可通过GIS格式接入模型。在LEACHG中，各数据文件组分从与栅格ID值关联的输入数据文件库中选取。例如，若某土地利用栅格单元的ID为23，则LEACHG将从名为Crops.023的库文件中读取数据。模型初始会读取所有相关栅格，识别土壤、土地利用与气象的唯一组合，并针对定义的时段对每种组合执行单次模拟。每次模拟将生成一套完整的LEACHM输出文件，以所用栅格ID值作为文件名标识。后处理环节可生成任意所需输出变量的栅格数据，如土壤剖面排水量、实际蒸散发量或灌溉施用量，同时生成以水深与体积为单位的水量平衡组分汇总结果，并为地下水流模型MODFLOW生成输入数据文件。
LEACHM代码采用FORTRAN语言编写。该代码会持续迭代优化，以适配特定项目及后处理环节的需求；相关事宜可联系约翰·赫特森博士（[e-mail]）。LEACHM模型的模拟时段可延长，但需修改输入数据文件并获取或生成所需的气候与土地利用数据集。
模型开发过程中使用的所有数据集均与模型一同存储。
模型覆盖范围包括南澳大利亚州（SA）下南东地区的下石灰岩海岸指定井区、部分边境指定区域，以及涵盖其内的地下水流系统。