Identifying mountain-block recharge and groundwater contributions to surface waters in alluvial aquifers and the potential for increased flood risks with climate change
Abstract
Hydraulic gradient shifts within and between aquifers caused by climatic and water use change may affect mountain block recharge (MBR) from bedrock to alluvial aquifers. This change can reduce or increase groundwater recharge and baseflow contributions to surface waters. Quantifying recharge sources and groundwater emergence zones in alluvial aquifers are critical in identifying MBR and affects from climatic or water use change. Conceptual and numerical models of the Mississippi River Valley alluvial aquifer (MRVAA) in the south-central USA to date have considered MBR from the Ozark Plateaus aquifer system (Ozark system) to the MRVAA negligible. This view holds despite the Ozark system exhibiting increasing recharge concomitant with increasing annual rainfall. Documentation of MBR to alluvial aquifers in subtropical, humid climates, such as the MRVAA, remains understudied compared to semi-arid and arid regions, globally. This study examined MBR and groundwater contributions to selected wells and surface waters in southeast Missouri (MO) using end-member mixing analysis (EMMA). Ratios of Ca/Mg and [Ca2+] were controlled by three end members: 1, rainfall-runoff; 2, Ozark system groundwater; and 3, direct-rainfall MRVAA recharge. Results from the EMMA calculations showed Ozark-system contributions to the MRVAA at nearly 50% in wells near the Ozark-system/MRVAA boundary at various seasonal sampling periods. The EMMA also showed some measured surface-water ditches draining alluvial areas to have up to 40% Ozark-system groundwater and nearly 50% as total groundwater (TGC = Ozark system + direct-rainfall MRVAA recharge). Groundwater contributions from the Ozark system as MBR likely represent a significant component of recharge to the western MRVAA in southeast MO, but more groundwater constraints are needed. Here we show MBR contributions can be significant to alluvial-aquifer systems in subtropical, humid climates. With increasing rainfall over many bedrock-alluvial boundaries as is the case for southeast MO, greater MBR to alluvial aquifers may occur. Greater MBR to alluvial aquifers may, in turn, drive greater TGC to surface waters and reduce field-drainage capacity in surface waters increasing flood risk in alluvial areas due to combined MBR and rainfall extremes associated with climate change.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.H23C..05B