Monitoring the hydrology of the created pool and the reference pools

To support a similar habitat to that occuring in the existing vernal pools, the created pool must, at a minimum, replicate the physical aspects of the environment it is attempting to replace. This page will be updated in November at the end of each wet season (earlier in drought years) and will contain a hydrograph of the pools and a graph of the wetted percentage of the pools for that year, a table showing the hydroperiod of the pools over the entire monitoring period, and a table specifying the deepest water that was present in the pools each year. Photographs of the pools at varying stages through their wetting and drying cycles are also provided here.

Since the relatively wet year in 2001 when initial studies were conducted in the reference pools, Adelaide entered a very dry period characterised by runs of several drought years punctuated by occasional average rainfall years. Above average rainfall has not been a feature of this period.

Monitoring the pools during 2006-2008 inclusive characterised the pools during drought years - short hydroperiods allowed grassy upland vegetation to invade into the pool areas and prevented the full reproductive cylcle of many aquatic invertebrate species.

2009 received average rains, but the extreme dry of the preceding years meant that the soil soaked up much rain before free water was apparent in the vernal pools. Weather details including evaporation and rainfall from 1942 to the present have been maintained at Dry Creek. These records for rainfall received in previous years show that 2008 was in the lowest 14% of records, 2007 rainfall was in the lowest 30% and 2006 was in the lowest 2%.

In 2009, with average rainfall, the pools all held water for an extended period, resulting in seeds setting on vernal pool species that require longer periods of inundation such as Amphibromus nervosus, Wilsonia rotundifolia and Limosella australis.

The rains of 2010 came late and totalled close to the long-term average. The additional warmth of those later months allowed the pools to dry up quicker than they would had the same quantum of rain arrived earlier in the year. Even so, the hydroperiod was long enough for seeds to set on many vernal pool plant species, although the Amphibromus nervosus seeded only very sparsely. Invertebrates caught in Pool 2 in 2010 included short-lived species that were fully mature, and some species that were longer lived. These latter (including a species of Lynceus, a clam shrimp) had very few sexually mature specimens when the pools dried up, with the majority of collected speciments being juveniles. The presence of these longer lived species in the existing pools suggests that the constructed pool will need to regularly have a hydroperiod in excess of 90 days for it to be able to support a similar assemblage.

2011 saw a return to a shorter hydroperiod, but despite this the last three years have seen the constructed pool's hydroperiod falling within the period displayed by the two reference pools. This contrasts with the first three years after construction when the constructed pool's hydroperiod exceeded that of either reference pool. This year, its depth also fell within the range displayed by the reference pools.

The drought that occurred immediately after the construction of the new pool has led to a revision in the period of time predicted for the new pool to approximate the conditions of the existing, reference pools. Prior to construction it was thought that 10-15 years may see a convergence, based on the speed of observable changes visible in historic aerial photography. The drought, however has had a very significant impact on the maturation of vernal pool vegetation, including slowing the development of a thick organic layer lining the pool. Thus, it is considered likely that convergence of hydrological and vegetative conditions may take in excess of twenty years to achieve, even though the morphology of the constructed pool matches quite closely that of the existing pools. Convergence in hydrology and vegetative habitat with the existing pools is essential if the pools are to support a similar faunal biodiversity.

Hydroperiod

Pool depth at deepest over the season

Depth and wetted transects over time

Model hydrographs for each year

Several approaches to modelling the hydrology of the pools have been taken over the monitoring period. The hydrographs above are based on a "water balance" approach. The pools are so small that they are affected by even minimal fluctuations in local environmental aspects and modelling attempts are therefore imprecise. The method is reasonably accurate in dealing with seepage and evaporation losses in the pools but runoff varies dramatically depending on the soil moisture bank existing at any given time. The models do reveal the pools' hydroperiods and change in water depth over each year. Actual water depth measurements are provided as point data in the graphs.

Weather records

Weather records for 2011, and comparison with historic weather deciles, are provided in the graphs below. They show average accumulated rainfall for the year, after the New Year started with a continuations of last year's rather wet summer. This year's autumn and winter rainfall was very low, only returning to slightly above average in August and September. Despite the overall average rainfall for the year, evaporation was slightly lower than normal due to the colder conditions early in the year.

Photographs

The first wetting of the new pool, 10 days after construction (10 May 2006)
Remediated pool 4, after docks were removed in 2007 - resulting in a new set of weeds to deal with!	Reference pool 2, end of drying phase in 2007 with Eleocharis (common spike rush) just starting to brown off
The constructed pool at the end of the drying phase in 2007 with the ring of vegetation gradually working its way towards the centre of the pool

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