Flood events have been shown to push huge groundwater discharges out of drained floodplains.

New research led by Southern Cross University has shown pulses of groundwater from agricultural floodplains in the Tweed Valley region are only released following flood events, while for the rest of the year groundwater is stored in the floodplain.

The paper; ‘Constraining the annual groundwater contribution to the water balance of an agricultural floodplain using radon: The importance of floods’, shows how floods and groundwater control the hydrology of floodplains.

“When put into perspective, our work shows that maintaining very shallow drains helps to keep the groundwater within the landscape and reduce greenhouse emissions,” PhD candidate Jackie Webb said.

“Cane farms in the Tweed Valley are near sea level and during floods they become fully inundated, so when that drains away it makes the groundwater seep out as well.”

Jackie used novel measuring technology and discovered groundwater dominated the drains immediately after floods.

“This research gives us insights into how to manage some of the pollutant impacts on our local rivers and estuaries. The results of this study can also help inform farmers on how to best manage their properties to reduce nutrient losses from the soil,” she said.

“We just witnessed one of the largest flood of the century. If these events become more frequent then we are likely to see more groundwater released from agricultural floodplains, which could have implications for downstream water quality and water storage.”

Jackie’s research was inspired by previous work where she discovered the implications of flood events in causing large greenhouse gas emissions from agricultural drains.

“Agricultural drains from these carbon rich systems can be hotspots for carbon dioxide and methane emissions,” Jackie said.

“These large greenhouse gas releases were observed following flood events, and in the case of carbon dioxide can now be linked to these coinciding groundwater pulses.

“However, the sooner the floodplain hydrology returns to normal conditions after these flood events the quicker the greenhouse emissions return to insignificant levels, highlighting the importance of hydrology management in these flood-prone landscapes.”