Lake Broadwater EarthCache
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Situated 30kms by road from Dalby
Lake Broadwater is the focal point of a 1,212 ha conservation park situated in one of the most intensively cultivated agricultural districts in Queensland. It is listed in the Directory of Nationally Important Wetlands and is an excellent example of a semi-permanent freshwater lake. This is the only large lake of its kind on the Darling Downs. The lake fills only after heavy rains and when full is up to 3–4 m deep. It dries out periodically, sometimes for lengthy periods.
The conservation park is also one of a few locations on the northern Darling Downs where the landforms and soil types of the region remain uncultivated or ungrazed. Resembling a large tadpole from the air, Lake Broadwater lies on a broad alluvial plain which drains northwards into the Condamine River via Wilkie Creek. It is fed from two ephemeral streams (Broadwater and Surveyor’s gullies) draining a local catchment of about 6,000 ha, most of which lies outside the park. Occasionally the lake floods during periods of summer rainfall, and may also dry out completely.
Floodplain, also called Alluvial Plain is a flat land area adjacent to a stream, composed of unconsolidated sedimentary deposits (alluvium) and subject to periodic inundation by the stream.
Ephemeral streams are watercourses that do not have surface water flow for the entire year. They are also called: seasonal streams, intermittent streams, episodic streams or temporary streams. Within this group of rivers and streams there is a wide variety of flow regimes. Some depend on rain events and may only flow for a few weeks, a year or less often. Others flow reliably for more than six months each year. There are classification schemes for these streams based on flow regime type. However, in reality these streams form a continuum of time spent inundated and may vary greatly in flow regime from year to year. Also, the classification schemes do not necessarily reflect the ecology or use of these systems by plants and animals. Water sources for ephemeral streams may be groundwater and/or surface run‑off. Consequently, developments that rely on groundwater as well as those that use surface water can affect flows in ephemeral streams.
A low gravelly ridge divides Lake Broadwater from the alluvial plains along the Condamine River to the north. Geomorphologists suggest that the lake itself was probably formed when high energy floodwaters spilling from the Condamine River gouged out a weak section of soil to form a depression. Subsequent high energy flood events would have continued to scoop it out and once the lake was deep enough, trees and shrubs could not grow on the bottom. Vegetation which has grown up around the lake over time has acted as a silt trap and created a low levee around the lake. Survey records show that the lake has changed little since 1877, however it is slowly getting shallower over time.
Soil types differ throughout the park and range from heavy black soil to light loams over clays, interspersed with sand and gravel ridges. Dark alluvial soils deposited as silt make up the floodways. Of the four wetland communities recognised at the lake, the open water communities and lake edge communities are regarded as the most important in ecological terms. The other described here are Riparian and Marsh communities. All of which have an ongoing effect on the survival of this fragile and ever changing unique wonder. The park preserves valuable remnants of the vegetation types which once covered the western Downs before European settlement. Many are now uncommon elsewhere due to agricultural development. Four hundred and fifty species of plants have been identified in the park, along with at least 30 mammals, 55 reptiles, 22 frogs, numerous fish and a myriad of invertebrates.
The Soil - STAGE3 S27 20.093 E151 05.890 Question 4: What is the soil type here? Heavy black soil, light loams, clay or sand?
The Ridge - STAGE2 S27 19.965 E151 05.770 Question 3: Beyond this area are alluvial plains. Describe the surface and of the land in the immediate area around you?
The Stream - STAGE1 S27 21.416 E151 05.668 Question 1: What type of steam system is evident here? Question 2: What type of water source do you think feeds this area?
A great place to picnic, bird watch, fish, camp, bushwalk or just chill out.
Congratulations to Geo~Gypsies for their excellent FTF
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