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，即水管理版本的Topnet，是犹他州立大学WRIA 1流域管理项目（Tarboton, 2007）的成果。该模型版本是在新西兰国家水文与气象研究所（NIWA）与犹他州立大学（Bandaragoda et al., 2004; Ibbitt and Woods, 2004）合作开发的Topnet模型基础上演化而来，该模型结合了TOPMODEL（Beven and Kirkby, 1979; Beven et al., 1995a）的概念，以模拟相对较小的流域并实现河道路由。这种方法提供了一种适用于大型流域的建模系统，其中较大流域内的较小流域作为模型单元。

在Topnet-WM中，空间变异性通过将流域区域划分为河道尺度的模型单元来表示。在河道内，模型构建本质上是集中的，但包括一些子网格变异性的参数化，尤其是（1）湿度指数，用于参数化土壤水分的变异性；（2）耗竭曲线，用于参数化积雪水当量的变异性；（3）灌溉面积的比例；（4）人工排水区。在河道内的多个节点可以指定地表径流和基流为模型输出。因此，该模型可以归类为半分布式。

Topnet-WM在原始Beven和Kirkby TOPMODEL的基础上增加了许多改进，例如：（1）采用美国土木工程师协会（ASCE）标准化的Penman-Monteith方法计算参考蒸散量（Allen et al., 2005; Jensen et al., 1990）；（2）使用犹他州能量平衡积雪融化模型（Tarboton et al., 1995a）计算积雪融化；（3）将模型单元划分为代表灌溉和非灌溉区域的独立组件；（4）引入人工排水来表征沟渠和管排区对径流响应的影响；（5）将模型单元划分为透水区和非透水区，以允许表征城市化；（6）在多种管理选项下提供水资源调配和储存的选项；（7）计算水资源使用和实施水权规则的组件。

基于分布式水文模型Topnet-WM，将估算Lower Nooksack水资源预算。Lower Nooksack水资源预算包括更新数据输入和模型校准，这需要深入理解模型如何表示物理水文过程。为了指导模型输入的开发和模型输出的分析，项目团队已编辑和审查了WRIA 1水管理项目第三阶段任务4.1报告（Tarboton, 2007）的部分内容，并将其纳入以下Topnet-WM模型的通用描述中。本章提供了Topnet-WM使用以将数据输入转换为模型输出的模型过程细节。

本资源是Lower Nooksack水资源预算（LNWB）资源集合的一个子集。