LNWB Ch02 Model Processes

Overview: Topnet-WM refers to the Water Management version of Topnet developed as a work product for the Utah State University WRIA 1 Watershed Management Project (Tarboton, 2007). This version of the model evolved from the Topnet Model developed in a collaboration between NIWA New Zealand and Utah State University (Bandaragoda et al., 2004; Ibbitt and Woods, 2004) that combines TOPMODEL concepts (Beven and Kirkby, 1979; Beven et al., 1995a) for the simulation of relatively small drainages combined with channel routing. This approach provides a modeling system that can be applied over large watersheds using smaller drainages within the large watershed as model elements. In Topnet-WM, spatial variability is represented by subdividing the watershed domain into model elements at the scale of drainages. Within drainages, the modeling is essentially lumped but includes parameterization of some subgrid variability, notably (1) the wetness index, used to parameterize the variability of soil moisture, (2) a depletion curve, used to parameterize the variability of snow water equivalent, (3) the fraction of area that is irrigated, and (4) areas with artificial drainage. Surface runoff and baseflow can be designated as model outputs at multiple nodes within a drainage. The model may thus be classified as semi-distributed. Topnet-WM includes many enhancements beyond the original Beven and Kirkby TOPMODEL, such as: (1) calculation of reference evapotranspiration using the ASCE standardized Penman-Monteith method (Allen et al., 2005; Jensen et al., 1990); (2) calculation of snowmelt using the Utah Energy Balance Snowmelt model (Tarboton et al., 1995a); (3) the partition of model elements into separate components representing irrigated and non-irrigated areas; (4) artificial drainage to represent the effect of ditch and tile drained areas on the runoff response; (5) the partition of the model elements into pervious and impervious areas to allow representation of urbanization; (6) options for the diversion and storage of water under different management options; and (7) components to calculate water use and implement water right rules. The Lower Nooksack Water Budget will be estimated based on the distributed hydrologic model, Topnet-WM. The Lower Nooksack Water Budget included updating the data inputs and model calibration, which requires a thorough understanding of how the model represents physical hydrologic processes. In order to guide the development of model inputs and analysis of model outputs, the project team has edited and reviewed portions of the WRIA 1 Water Management Project Phase III Task 4.1 report (Tarboton, 2007) to include in the general description of the Topnet-WM model that follows. This chapter provides reference to the details of the model processes used by Topnet-WM to convert data inputs into model outputs. This resource is a subset of the Lower Nooksack Water Budget (LNWB) Collection Resource.概述： Topnet-WM即Topnet水资源管理版本，是为犹他州立大学WRIA 1流域管理项目开发的工作成果（Tarboton, 2007）。该模型版本源自新西兰NIWA与犹他州立大学合作开发的Topnet模型（Bandaragoda等, 2004；Ibbitt与Woods, 2004），结合了TOPMODEL理论（Beven与Kirkby, 1979；Beven等, 1995a），用于模拟小型汇水区并配套河道汇流演算。该方法构建的建模系统可应用于大型流域，将大型流域内的小型汇水区作为模型单元。 在Topnet-WM中，空间变异性通过将流域范围划分为以汇水为尺度的模型单元来表征。在汇水区内部，建模采用集总式框架，但纳入部分次网格变异性的参数化方案，具体包括：(1) 用于表征土壤水分变异性的湿润指数；(2) 用于参数化雪水当量变异性的消退曲线；(3) 灌溉面积占比；(4) 人工排水区域。可将地表径流与基流设定为汇水区内多个节点的模型输出，因此该模型可归类为半分布式模型。 Topnet-WM相较于原始的Beven与Kirkby版TOPMODEL新增了多项改进，具体包括：(1) 采用美国土木工程师学会（ASCE）标准彭曼-蒙特斯（Penman-Monteith）法计算参考蒸散发（Allen等, 2005；Jensen等, 1990）；(2) 采用犹他州能量平衡融雪模型计算融雪量（Tarboton等, 1995a）；(3) 将模型单元划分为灌溉区与非灌溉区两个独立组分；(4) 加入人工排水模块，表征沟渠与暗管排水区域对径流响应的影响；(5) 将模型单元划分为透水与不透水区域，以表征城市化过程；(6) 支持不同管理方案下的水资源引水与蓄水设置；(7) 加入计算水资源用量与执行水权规则的模块。 下努克萨克水收支（Lower Nooksack Water Budget）将基于分布式水文模型Topnet-WM进行估算。该水收支项目包含数据输入更新与模型率定环节，这需要深入理解模型对物理水文过程的表征方式。为指导模型输入开发与模型输出分析，项目团队对WRIA 1流域管理项目第三阶段任务4.1报告（Tarboton, 2007）的部分内容进行了编辑与审阅，将其纳入下文的Topnet-WM模型通用描述中。本章旨在详述Topnet-WM将输入数据转换为模型输出所涉及的模型过程细节。 本数据集为下努克萨克水收支（LNWB）合集资源的子集。