Groundwater Occurrence in the Shepparton Irrigation Region

Note Number: GW0022
Published: September 2002
Reviewed:

Introduction

Groundwater is part of the water cycle. When it rains, some water is evaporated, some forms runoff into drains, rivers and streams and some seeps into the ground. Water in the soil that is not used by plant roots travels down deeper until it reaches a level known as the watertable. This is a saturated zone where all the spaces between the soil or bedrock are filled with water. Water in this saturated zone beneath the watertable is called groundwater.

Groundwater in the Shepparton Irrigation Region

The Shepparton Irrigation Region is very much like a basin that has been filled up with fine and coarse sediment over thousands of years. The surrounding bedrock outcrops of the Strathbogie Ranges the Mt. Camel Ranges at Corop and other landmarks such as Mt. Major at Dookie, are the exposed walls of the basin and serve as the major (but not the only) recharge points for the groundwater stores beneath our agricultural crops.

Aquifers in the Shepparton Irrigation Region

The riverine plains of the Shepparton Irrigation Region are alluvial deposits having a comparatively flat surface. More recent ancestral streams deposited sediments over the top of the deep lead materials and bedrock. In these sediments, deposits of coarse (sand) material, referred to as aquifers are separated by less permeable clayey materials.

Aquifers occur at all depths in these sediments. These underground water-bearing layers of sand or gravel are capable of supplying significant quantities of water to bores or springs. Water quality in these aquifers becomes poorer with depth. High watertables have generally followed saturation of the aquifers in the uppermost 30 m.

Aquifers and Aquifer Types
Aquifers are layers of porous material such as sand, gravel or fractured rock in which the spaces or fractures are filled with water. In the Shepparton Irrigation Region they are commonly formed by old sandbars on rivers and streams being buried over time by sediments.

There are two types of aquifers:

• Unconfined: this aquifer is found below the surface between the soil (usually a sandy loam or loam) and a confining base (rock or heavy clay). The water in this aquifer is not under any pressure, as the soil above it will not restrict upward movement of water. Therefore, if a bore were sunk into   an unconfined aquifer the water would rise to the same level as the local watertable.
• Confined: this aquifer is, as the name suggests, confined between two beds of rock or clay. The top bed restricts the upward movement of groundwater. Unless heavily pumped, a confined aquifer is generally under pressure and if a bore were sunk into this aquifer, water would rise above the level of the local watertable.

What aquifers are pumped for irrigation?

An extensive network of unconfined aquifers ranging from near surface to 420 m beneath the ground occur within the Shepparton Irrigation Region. The main aquifers are found within the first 25 m. These are generally pumped for irrigation, stock and domestic use. Lowering the watertable and salinity control can be achieved by pumping from these shallow aquifers.

The confined Deep Lead system commonly found around the Murray-Valley area refers to groundwater stored at depths between 25 – 130 m. Town water supplies for Elmore, Katunga and Strathmerton are from this aquifer group. These aquifers are extensively used as a resource due to the good quality of the water.

Acknowledgments

This Information note was developed by Terry Batey, Tatura