Urban Salinity in Wagga Wagga:
Let’s get things nice and sparkly clear; Wagga Wagga is a rural Australian town which boasts approximately 57,000 residents. Ergo, this node will be of little to no concern to most, but this is Everything and this information is pertinent to someone.
1. Overview of Wagga Wagga.
2. De-watering bores pump station.
3. Emblen Park
4. Hardy Avenue
5. Calvary Hospital
6. The Showground
7. Evaporation basin
8. Charles Sturt University campus
9. Leavenworth Drive
10. Willans Hill on Red Hill Road
11. Botanical Gardens (Waterwise Garden)
1. Overview of Wagga Wagga:
Most of Wagga Wagga began and is (for the most part) located near the river’s floodplain (where salinity is unlikely to prove a problem: the issue mostly focuses on the lower slopes of Willans Hill). Growth of the city (including construction practices, the clearing of vegetation and other related symptoms) has seen recharge increase from 1mm/year to 15mm/year in rural areas and a far more drastic 50mm/year in urban areas. In general, Wagga suffers from salinity problems for much the same reason as the bulk of Australia does – low-relief country, sluggish rivers and impermeable clay soils conspire to cause a number of groundwater problems, notwithstanding a certain degree of negligence which has plagued the human approach to the natural world at large. Wagga Wagga’s specific problem is largely explained with reference to local groundwater systems and groundwater flow. Much of Wagga Wagga is situated in a large drainage basin with a small discharge point, preventing groundwater leaving easily. Similarly, the thick clay layer at the base of the slopes next to the floodplain prevents water passage.
Why is salinity a threat? Rising groundwater results in the addition of soluble salts such as sodium, calcium, magnesium, potassium, sulphates, and chlorides (dissolved from geologic materials with which the waters have been in contact) to higher soils and eventually to whatever may be situated on the surface. Evaporation and transpiration (plant uptake) of irrigation water eventually cause excessive amounts of salts to accumulate in soils unless adequate leaching and drainage are provided. Excessive soil salinity reduces yields by lowering plant stand and growth rate. The general rule is that a water table less than 2m below the surface and bearing a salt concentration of 1 ds/m or greater is a hazard to plant growth and a danger to structures. In reality, the type of soil and the plants or structures affected heavily influence these figures: clay soils are more susceptible to capillary action and, consequently, can bring saline water from a greater depth than could a predominantly sandy soil.
2. De-watering bores pump station:
Technological solutions have also proved their worth (alongside their great expense). One such solution is the de-watering bore (employed at the corner of Edward and Moorong Street Streets), which pumps from aquifers (underground beds of earth, gravel, or porous stone that yield water), some 40-65 metres below the surface (where the groundwater is significantly less salty: 0.9 dS/m from the deeper aquifer under Emblen Park, by contrast to 1.3 dS/m from the shallower aquifer in the same location). Piezometers are employed to record fluctuations in the height of the water table, in order to assess the pumps’ effectiveness.
The bores were designed with four primary purposes in mind. Namely, to determine:
• The effectiveness of groundwater pumping in lowering the watertable
• Changes to groundwater salinity with pumping over time
• Pumping rates needed to lower the watertable and
• Pump establishment and running costs.
The marginally increased salinisation of the Murrumbidgee River (an increase of approximately 0.5% or a little less than an extra ton to the estimated 1700 tons which otherwise flow past Wagga each day) is regarded as acceptable, both by the Wagga Wagga City Council and the EPA, who conferred a 5-year license upon the Council (on the provision that the salinity of groundwater does not rise above 2.5 dS/m) in light of the fact that dry land salinity has been markedly reduced. Monitoring continues to ascertain whether or not the increase has any detrimental effects. Concern exists, however, over the maintenance of the pumping system, due to probably-excessive expenses in the long term. Costs have included piezometer installation soil surveys and modelling ($100,000, donated by the NHT and DLWC who also paid for a percentage of the piezometer drilling and functioned in an advisory capacity), bore installation ($420,000), monitoring ($207,000 in the first year; this figure is expected to fall once the effects upon the river are better-known) and power ($37,600 per year).
As an addendum, it ought to be noted that the pumps are currently inactive, so as to measure the effect of the drought upon the watertable. Curiously, it continues to rise (albeit more slowly) and this has been ascribed to domestic and industrial over-watering (described in greater length later).
3. Emblen Park:
Standing as an example of rehabilitation is the Emblen Park demonstration site. Previously covered with lawn (and, consequently, heavily affected by saline groundwater), the park has now been converted to a salt-tolerant plant demonstration site. The park also contains a de-watering bore, the water pumped by which being used to water the park. This site is of great import because it demonstrates the above rehabilitative measures to the community – more importantly that it does so in a residential area itself suffering from the problem.
4. Hardy Avenue:
Contrary to many streets, Hardy Avenue (in a heavily salt-affected area) is geared specifically to combat salinity problems. Lawn-based nature strips have been discarded in favour of salt-tolerant shrubs and trees, so as to stall recharge. Hardy Avenue was chosen as a demonstration site because it is in a discharge area and has a very high watertable (1m from the surface, in some areas). Unlike many areas, residents (six, to be precise) volunteered to have their nature strips altered and henceforth to maintain the new plants. The total cost of this rehabilitation was $42,000; this site will be used to assess the potential benefits of further alterations of this kind.
5. Calvary Hospital:
In this area, there are many visible indications of salinity, including the corrosion of metal fixtures (taps, pipes, mailboxes, etc), the detrition of bricks, mortar and paint and the poor and sickly growth of many plant species. In some areas such as the Hospital’s car-park, rutting and potholing of road surfaces also occurs Curiously, this visible indication of danger to property has done little to affect real estate pricing in even the most direly troubled areas, perhaps indicative of continuing ignorance of the extent of danger the rising watertable offers (possibly exacerbated by the fact that not all houses or other structures show outward signs of salinity).
Some houses in the area do not possess stormwater outlets on the kerb and so continue to use backyard rubble pits, despite their illegality. One important conclusion to be reached from this area is that sub-surface drainage around houses is not an effective solution, as cracking may occur where the ground dries at different rates. This area also possesses a de-watering bore.
6. Showground:
Wagga Wagga’s groundwater/salinity problem was first identified during trotting track earthworks and unsuccessful attempts to revegetate the disturbed soil. When it was discovered that it was a dangerously high watertable (and not a lack of quality control in the batches of grass seeds, as had previously been believed to be the case), the Show Society (in May 1994) installed drainage pipes (1.2m underground and 7m apart) under the two inner ovals and planted salt-tolerant grasses. The pipes reduced waterlogging by pumping excess (and overwhelmingly saline) water from the soil into the river.
7. Evaporation Basin:
This pumping system was stopped in 1998 in favour of the evaporation basin, situated in the proximity of the Showgrounds (and due to recent New South Wales government regulations forbidding the draining of heavily saline groundwater into the river). Funding for the basins came from the Environmental Trust ($80,000), the EPA ($10,000) and the Wagga Wagga City Council ($200,000). First used in June of that year, the basin balances the amount of water flowing in from the Showground and leaving via evaporation.
Constructed of heavily-compacted clay, it has a surface area of 0.5ha and a depth of 1.7m. Its smaller, shallower counterpart was designed to enhance water evaporation, but primarily to allow for salt removal by earth-moving machinery as needed (which may, as a windfall, have industrial uses). The larger basin was designed solely to handler the volume of water from the Showground. The enduring greenery of the oval is testament to its success, despite colossal expense (which included investigation work, land committed to the basin, the construction of the basin, pipe and sub-surface drain installation and ongoing monitoring).
Specifically, the larger basin was created with the intent to:
• Ensure the ongoing use of the showground by controlling the height of the watertable upon which it is situated
• Safely dispose of groundwater, in order to prevent it from reaching the river and
• Test the effect of evaporation basins in reducing dry-land salinity in urban areas.
8. Charles Sturt University Campus:
Referring in large part to the abandoned, salt-affected playing field; the health of grasses and trees deteriorates further down the slope as the watertable nears the surface, the notable exception being the more salt-tolerant species (which still occasionally demonstrate stunted growth). Some houses level with or down slope of the abandoned playing field. The watertable has caused significant damage to the road as well, in areas where the two intersect. The nearby Juvenile Justice Centre suffers similar problems, especially with regard to buildings and fencing. The field has been recently sold by the state government to local developers and may now become a residential area, despite the general ill-health of the area.
9. Leavenworth Drive:
Tree and shrub plantings are one method long tried and proven and as such, many have taken place within Wagga Wagga (particularly to supplement other measures, such as the evaporation basin) since the Council first became aware of salinity issues. Since 1998, an effective revegetation plan has been set in place: some 100,000 trees and shrubs have been planted, involving many community groups, schools, businesses (such as Coles, which donated $20,000 to the planting of 4000 trees at the Dukes Creek Wetland Site) and council staff as part of a continuing awareness program. The EPA also contributed $92,000 toward this effort (as part of their Carbon Sink program). Existing plans intend to revegetate 22 ha of land for the next 30 years, with an emphasis placed on higher, hillier areas so as to reduce erosion and runoff at the same time). This, by necessity, involves community input and intervention. Leavenworth Drive provides a sample of this broad action.
10. Willans Hill (Red Hill Road):
The two issues of greatest import here are the effect of geology/soil types upon groundwater flow and the responsibility of all individuals within a catchment to take responsibility for it.
Rock cutting at the highest point of Red Hill Road shows a near-vertical slant to rock layers, an aspect which rapidly increases recharge. Also, house blocks cut into hills can have damp issues unrelated to the regional watertable; it is common practice to level off blocks before building, especially where houses are to be based upon concrete slabs. Ergo, if a house is built in this manner (or if a site is either filled with levelling soil which drains more quickly than the layer it is placed on or the imported soil drains poorly itself) damp effects may be witnessed and incorrectly attributed to salinity. Also, signs of waterlogging and salinity have appeared in higher-elevation areas, which can be a product of perched water-tables (where water is forced to the surface by underground rock structures).
In the latter case, those higher up a slope invariably affect those further down with their water use – to this end, Council has urged adherence to a number of steps to control domestic (especially outdoor use, which accounts for 53% of total domestic water usage and most directly affects the water table). Most of these steps focus on the planting of perennial native vegetation in favour of water-consumptive lawn, the careful use of water (particularly with regard to sprinklers and timers), maintenance of water systems, ecologically sound construction projects and becoming more active in thwarting salinity in the community at large.
11. Botanical Gardens – Waterwise Garden:
This section of the Botanical Gardens stands as an example to the community at large by virtue of its accessibility and applicability (it being a representation of an ecologically sound garden at a ‘home’ scale). So too is it important for being one of the first anti-salinity measures undertaken since the identification of salinity problems in the early 1990s.
Sources:
’Be Water Wise For Our Community’
Wagga Wagga groundwater map
’Indicators of Urban Salinity’
’Wagga Wagga Salinity Tour Guide’