Three-dimensional distribution of residence time metrics in the glaciated United States using metamodels trained on general numerical models

Water Resources Research
By: , and 

Links

Abstract

Residence time distribution (RTD) is a critically important characteristic of groundwater flow systems; however, it cannot be measured directly. RTD can be inferred from tracer data with analytical models (few parameters) or with numerical models (many parameters). The second approach permits more variation in system properties but is used less frequently than the first because large‐scale numerical models can be resource intensive. Using a novel automated approach, a set of 115 inexpensive general simulation models (GSMs) was used to create RTD metrics (fraction of young groundwater, defined as < 65 years old; mean travel time of young fraction; median travel time of old fraction; and mean path length). GSMs captured the general trends in measured tritium concentrations in 431 wells. Boosted Regression Tree metamodels were trained to predict these RTD metrics using available wall‐to‐wall hydrogeographic digital sets as explanatory features. The metamodels produced a three‐dimensional distribution of predictions throughout the glacial system that generally matched with the numerical model RTD metrics. In addition to the expected importance of aquifer thickness and recharge rate in predicting RTD metrics, two new data sets, Multi‐Order Hydrologic Position (MOHP) and hydrogeologic terrane were important predictors. These variables by themselves produced metamodels with Nash‐Sutcliffe efficiency close to the full metamodel. Metamodel predictions showed that the volume of young groundwater stored in the glaciated U.S. is about 6,000 km3, or about 0.5% of globally stored young groundwater.

Publication type Article
Publication Subtype Journal Article
Title Three-dimensional distribution of residence time metrics in the glaciated United States using metamodels trained on general numerical models
Series title Water Resources Research
DOI https://doi.org/10.1029/2020WR027335
Volume 57
Issue 2
Year Published 2021
Language English
Publisher American Geophysical Union
Contributing office(s) WMA - Earth System Processes Division
Description ee2020WR027335
Google Analytics Metrics Metrics page
Additional publication details