Numerical model development of coupled surface-groundwater interactions in the Nooksack Basin

Surface-groundwater interactions are simulated using a loose coupling (3 steps) of the Topnet-WM surface water model and the MODFLOW groundwater model. Data included here are draft results of the surface model and final results of the coupled surface-groundwater model. Draft surface model outputs (recharge) was used as a model drivers for the groundwater model (Step 1). The groundwater model was run, informed by surface water management, to generate depth to water table outputs (Step 2). The depth to groundwater from Step 2 was used to update the surface model subsurface state variable twice per year. The steady state groundwater level per drainage with no irrigation was used to update the model each March 1, to improve saturated winter subsurface conditions. The steady state groundwater model with irrigation was used to update the surface water model subsurface state variable each October 1. Final model results are available for streamflow and water budget components on a daily timestep from 1955-2010 as part of the project “Development of a Numerical Groundwater Model for the Lynden/Everson/Nooksack/Sumas (LENS) Area of Whatcom County” for Phase 4 – Numerical Model Development for the WRIA 1 Watershed Management Project Joint Board (Joint Board).

This work was developed to provide updated model code and recharge estimates of Bertrand and WRIA Drainage from Surface Water Modeling with Water Management for coupling to the MODFLOW groundwater model. Subsurface recharge is a surface water model (Topnet-WM) output that can be used as an independent constraint on the groundwater recharge that is specified for the groundwater model (MODFLOW). This will help to ensure that the surface water and groundwater models are internally consistent. The surface water modeling will help to identify a longterm period of representative climatic conditions and resulting groundwater recharge, which can serve as input over a representative time period and for the calibration of a steadystate groundwater model. The surface water modeling also provide important insights about stream baseflows for calibrating the groundwater model. The analysis of surface water and groundwater conditions is conducted over a large model domain with progressively increasing resolution (e.g. with increased focus in Bertrand) where we are addressing specific questions of drainage impacts and groundwater withdrawal impacts from wells on surface water. The current model domain of the surface water flow model, Topnet-WM, includes the entire WRIA 1 watershed, but calibration and water use inputs have only been refined for the Lower Nooksack Subbasin portion of the basin with additional model development was previously completed in the Bertrand Creek drainages resulting in the surface model resolution being increased from a single watershed average to 46 sub-drainages per watershed. The following steps estimate groundwater recharge in the conceptual/numerical groundwater model:

A distribution of recharge was developed for the entire conceptual/numerical model domain WRIA1, inclusive of the LENS domain. Model simulations for GW model test coupling with outputs for Water Management On. Of the 172 modeled Nooksack drainages, those with water management data available are primarily in the Lower Nooksack.

A distribution of recharge was developed for the entire conceptual/numerical model domain in Bertrand Creek. Model simulations for GW model test coupling with outputs for Water Management On. The greater resolution groundwater recharge estimates for Bertrand Creek sub-drainages developed from the 2016 Topnet-WM model are also used as input to the groundwater model.

For developers: the original Topnet-WM model written in Fortran was recoded in C++ and new model output files were designed for groundwater model coupling. Model software code and related files are available at https://github.com/ChristinaB/Topnet-WM.

地表水与地下水相互作用模拟采用Topnet-WM地表水模型与MODFLOW地下水模型的松散耦合（三步法）。本数据集包含地表模型初步结果和耦合地表-地下水模型的最终结果。地表模型初步输出（补给量）被用作地下水模型的驱动因素（步骤1）。地下水模型在考虑地表水管理的情况下运行，以生成地下水位输出（步骤2）。每半年更新一次地表模型地下状态变量，使用步骤2中获得的地下水深度。无灌溉条件下的稳定状态地下水水位于每年的3月1日更新模型，以改善冬季饱和地下条件。有灌溉的稳定状态地下水模型于每年的10月1日更新地表水模型地下状态变量。最终模型结果可用于1955-2010年间每日时间步长的河流流量和水文预算组件，作为“为Whatcom县Lynden/Everson/Nooksack/Sumas（LENS）区域（LENS区域）”项目第四阶段——WRIA 1流域管理项目联合委员会（联合委员会）的“开发数值地下水模型”的一部分。本研究旨在提供更新后的模型代码和地表水建模中Bertrand和WRIA排水区域的补给估计，以便与MODFLOW地下水模型耦合。地下补给是地表水模型（Topnet-WM）的输出，可以用作对地下水模型（MODFLOW）中指定的地下水补给量进行独立约束，从而确保地表水和地下水模型内部一致性。地表水建模有助于识别具有代表性的长期气候条件和由此产生的地下水补给，这些可以作为代表性时间段的输入和稳定状态地下水模型的校准。地表水建模还提供了关于基流校准地下水模型的重要见解。地表水和地下水条件分析在一个大模型区域内进行，分辨率逐渐提高（例如，在Bertrand地区增加关注），我们正在解决关于排水影响和井对地表水提取影响的特定问题。当前地表水流模型Topnet-WM的模型区域包括整个WRIA 1流域，但校准和水使用输入仅针对流域下诺斯克溪部分进行了细化；之前在Bertrand溪流域完成了额外的模型开发，导致地表模型分辨率从单一流域平均增加到每个流域46个子排水区域。以下步骤估计概念/数值地下水模型中的补给分布：为整个概念/数值模型域WRIA1（包括LENS域）开发补给分布。进行GW模型测试耦合的模拟，并输出水管理数据。在172个模拟的诺斯克溪流域中，有水管理数据的主要位于下诺斯克溪。为Bertrand溪流域的概念/数值模型域开发补给分布。进行GW模型测试耦合的模拟，并输出水管理数据。从2016年Topnet-WM模型中开发的更高分辨率Bertrand溪子排水区域补给估计也用作地下水模型的输入。对于开发者：原始用Fortran编写的Topnet-WM模型已被重写为C++，并为地下水模型耦合设计了新的模型输出文件。模型软件代码和相关文件可在https://github.com/ChristinaB/Topnet-WM上找到。