Howard Springs Nature Park: Synthesis of What We Know
Spring flows
The bore and springs in the Nature Park are fed by the groundwater aquifer.
The spring flow decreases progressively from about 300 litres/second at the height of the Wet season in February to an average of about 20 litres/second at the end of the Dry season in November. After a series of years with below average rainfall the spring may stop flowing. The chemistry of the spring water remains constant throughout the year although the bore sometimes shows the presence of saline waters when the aquifer is low.
Since the spring is connected to the same aquifer that is accessed by bores in the surrounding region, there is potential for drawdown of the aquifer to affect spring flow. Results from a monitoring bore in the Howard Springs area that was established in the 1970's, before significant rural development took place, provides insight into what is happening. The plot of “depth to the water level over time” indicates that the seasonal rise and fall of groundwater levels under natural conditions was 6 to 8m in the 1970’s. However, since the mid 1980’s, the effect of “drawdown” has become evident with the total seasonal decline in water levels exceeding 15m. The figure below provides evidence that drawdown in the region is a real and measurable quantity.
Figure 3 Groundwater Monitoring Record - Bore RN7151 Howard Springs
What are the implications of draw down on the aquifer for water flow from Howard Springs? While direct flow from the spring itself has only been measured sporadically since 1999, it has been observed as ceasing to flow by the end of October in most years since 2002.
Although we don’t have a good record of flows from the spring itself, a bore approximately 100m from the spring, has been regularly monitored since 1980. The water level record from this bore is shown below.
Figure 4
Groundwater Monitoring Record - Bore RN9421 Howard Springs
By correlating the spring flow observations and the bore level measurements it has established that the spring ceases to flow when the water level reaches a depth of 6.71m in the bore.
This bore monitoring record infers that between 1980 and 1990, the spring did not cease to flow as groundwater levels did not reach the critical depth. However, after some poor wet seasons in the early 1990’s, it is likely that the spring did cease to flow. Monitoring of flow from the spring in the 2000’s indicates that it has ceased to flow in most years.
There is now evidence that recent cessation of the springs flow towards the end of the dry seasons is due to the amount of groundwater pumping (ie. drawdown), particularly from the areas surrounding the spring. This is discussed further in the accompanying document Howard Springs and Groundwater in the Rural Darwin Area.
Since water flow from the spring flushes the waterhole, these changes to spring flow are likely to have had an impact on water quality
