Tools to Estimate Groundwater Levels in the Presence of Changes of Precipitation and Pumping

Jessica Haucke,George Kraft,Katherine Clancy

doi:10.4236/jwarp.2016.812084

Abstract

Central Wisconsin has the greatest density of high capacity wells in the state, most of which are used for agricultural irrigation. Irrigated agriculture has been growing steadily in the region since the 1950’s, when irrigation systems and high capacity wells became inexpensive and easy to install. Recent low lake and river levels have increased concerns that unregulated groundwater pumping for irrigation will undermine the availability of groundwater to support surface waters and domestic uses. Some research has quantified the magnitude of groundwater level declines due to irrigation pumping, but no studies have identified its relation to climatic precipitation changes. Changes in precipitation can appear to exacerbate or mask the effect of groundwater pumping. In this study, four groundwater monitoring wells and five climate stations were examined for shifts in groundwater levels and precipitation changes. Through statistical analysis, significant precipitation increases were identified in the southern part of the study area which averaged 2.7 mm per year, but no significant change was determined for the northern portion. Bivariate analysis identified water level declines within the region in the years 1974, 1992 and 1999 for irrigated land covers. Multiple regression analysis explained, predicted and quantified the interaction between precipitation and pumping. Wells located in areas with many high capacity wells showed a decline in water levels of up to 1.28 meters. In the southern portion of the study area where increases in precipitation occurred, this decline was thought to be masked. Results for one region (Plover) agreed with a previously published calibrated groundwater model, which demonstrates that this statistical method may be used to separate the impact of groundwater pumping from changing precipitation, even where observation well data are not widely available.

Highlights

Groundwater is considered one of our most important natural resources
The time period 1955-2008 was used for all precipitation data sets because data from one of the COOP climate stations (Montello) began in 1955
Groundwater levels have increased in other regions due to a suggested step increase in precipitation

Summary

Introduction

Groundwater is considered one of our most important natural resources. Since the early to mid-twentieth century, groundwater withdrawals have drastically increased due to changes in irrigation technology [1]. Recent studies estimate that groundwater extraction across the globe has tripled in the last 50 years and is increasing in many countries at an annual growth rate of between 1% - 2% [2] [3] [4] Climate variability brings another interesting set of challenges for groundwater management. Regions which experience an increase in annual precipitation may see lower recharge due to a larger percentage of precipitation occurring as high intensity events [5]. Another challenge is associated with groundwater’s perceived higher resiliency to climate variability. In either an attempt to protect surface waters or ensure a more reliable water source, the expectation is that many users will turn to groundwater as their source of water [2] [6] [7]

Objectives

Methods

Results

Conclusion