On the other hand , groundwater may be high in nitrate concentration; the movement of such groundwater into a waterway may help increase the N:P ratio and help favour the growth of green algae over blue-greens. G ro und water inflows high in sul fa te concentration added to the algal orga nic matter (in the bottom sediments) suitable for the metabolism of sulfate-reducing bacteria can activate the bacteria in the sediments. T he bottom water waterway can become anoxic, with resolubilisation of some of the phosphorus bound in the sediments. T he resulting feedback can release a pulse of soluble reactable phosphorus into the water column , causing an algal bloom (Donnelly et al, 1992). Such conditions exist along the Darling River, fo r example. Although sulfate concentrations in the river are generally not high (10-3 0 mg/ L), in early 1991 sulfate concentrations of 70 mg/ L were measured in sections of the ri ver, fo r example near . Louth , indicating possible inflow sul fa terich saline groundwater. Also, at times of low ri ver flow, saline gro und water infl ows into ri ve r bed depressions may occur (examples are known fo r the Darling Ri ver). T he cha nge in the ionic balance of the ri ver caused by these inflows could cause sediment flo cculation , res ulting in mu ch lower t ur bidi ties co in cid in g wit h low fl ow a nd war m condi tions. If the ri ver water has high concentrations of phosphorus (such as in t he D ar lin g Rive r) , a lga l growth can commence. T he need to fur ther understand the relationship between groundwater and bluegreen algae has been recognised by the NSW
RJ NEWMAN continued f rom page 26 about 100 m deep. Fibreglass slotted casing has been used at Woolpunda, however, open hole completions, with surface casing, have been used at Waikerie. Pipelines greater than 300 mm diameter h ave been laid in HOBAS glass reinforced plastic and smaller pipes are uPYC. Pumps are Grundfos stainless steel grade 316 o r better a nd a re suspe nd ed on Wellmaster flexible risers for easy withdraw! fo r maintenance. A crane truck is used to withdraw a pump in 20 minutes . The schemes have involved a major upgrade of the local electricity distrubiton system . Land acquisition has involved close to 100 property owners and has requi red continuous consultation with the local community.
IMPLEMENTATION A ND MONITORING Th e Woolpund a sch em e has been implemented in fou r phases. Initially the first 24 bores were pumped at twice the longterm design rate as the first half of the pipeline became available. This accelerates
36
WATER Dece mber 1992
Blue-Green Algae Task Force. In its Fina l Repo rt (1 992) t h e Task Froce h as recommended research into an assessment of nu trients iri the sedi ments of water bodies, and an assessment of the ro le of gro undwater in triggering algal blooms in rivers such as the Darling.
ALGAL BW OM IMPACTS AND GROUNDWATER A lgae contingency plans A lgae co ntingency pl a ns have been developed in many states, to varying degrees, to plan for the effecti ve management and co ntro l of a lga l bl oo ms, in o rd er to minimise their occurrence and impact. T he plans including mo nitorin g, communi cations and response components. For states such as News South Wales, Victoria and South Australia where most communities re ly o n s urface wa ter suppli es, th e contingency plans are costly and need to be comprehensive (including the identification of alternative water sources) to safeguard public health . However, the algae conti ngency plans fo r many regions in Q ueensland and Nort hern Territory are simpler and far less costly. Becau se d o mes ti c water suppli es a re ground water sourced, public health issues in these regions relate onl y to recreational use of surface waters. Water suppl y From the experience of the 1991/ 92 summer, many communities currently on surface water supply will be considering the use of groundwater as an alternative (du ring algal blooms) or as a replacement source.
t he a bilit y o f t he sc hem e to remove groundwater fro m 'storage'. The Waikerie Scheme will be built in two phases. the details of Phase Two will be verified after operation of Phase One fo r at least one year. The schemes will progressively become fully effecti ve over about fi ve years. An intensive monitoring system has been developed including a detailed assessment o f the operationa l performance of the bore pumps, salinity and flow measurements in th e ri ve r toget he r with t he reg ul ar monitoring of about 150 observation wells. It is imperati ve that the scheme continues to operate at peak effi ciency because of the high power requi rements. Pumping water of this salinity is not stra ightfo rward. Corrosion is a lways a concer. Another problem which has had to be overcome is the effect of chemical and biological deposition in the pumps and pipelines. Chlorination of the pumps and ri sers has b ee n impl eme n ted u sin g electrolysis of the saline water. At the time of writing the Woolpunda scheme has been progressively implemented over the last year or two. It is still too early to see convincing evidence of interceptio n in . t he ri ve r, bu t th e des ig ne rs take
Pas to ralists, fa rmers and irrigators will also be considering the greater security of water quality provided by a ground water source. For irrigators in particular, the advantage of using groundwater include security of qua lity, greater securi ty of quantity, and lower maintenance costs of irrigati o n equipm ent (n o clogging of pumps, pipelines and sprinklers with algal biomass). These advantages need to be weighed against the generally higher cost of extracting gro undwater.
CONCLUSIONS While public attention on the blue-green algae problem has foc used on our sur face water reso urces, there is also an important relatio n shi p with gro undwa ter. A n understanding of the re lationship of the complexity of causes and effects is vital if the ro le of groundwater is to be understood, a nd if sucess ful ma nage ment is to be im p le m ente d. T he ava il a bili ty of ground water influences the structure and cost of algal contingency plans, and the provision of water supplies fo r a ra nge of uses.
REFERENCES Donnell y, T H ., O lley, J .M. , M u rray, A.S. a nd Wasson R.J. (1992) A lgal Blooms in the Darling River: 'Run
of River' St udy Wentworth to Collarenabri December 1991; CS I RO D ivision o f Water Resources C o nsul tantcy Report No. 92/ 13 J uly 1992 . New South Wa les Blue-Green A lga e Tas k Force (1 992);
Blue- Green A lgae: Final Rep ort of the Task Force; pub lis hed by the NSW Depa rtm en t of Wate r Resources; Augu st I 992. W illi ams R.M . (199 1); Groundwater inflow lo the
Darling River Mungindi to Wentworth: Run of River Study (1990/ 91); NSW D epart m e nt of Wat er Resources, Technica l Services Di visio n Re port TS9 1.04 1; A ugusl 199 1.
co n f id ence fr o m th e res ul ts of th e production drilling program which bear out the interpretations of the investigations. T he drawdown cones aro und the production bores are continuing to expand and are now approaching the ri ver. Some 180 000 tonnes of salt has been di verted fro m the aquifers near the ri ver.
ACKNOWLEDGEMENTS T hese proj ect have involved a team of inves tigators, designers and constructors and consultants over many years. the author expresses particular recogni tion of the efforts o f Ken Smi th a nd Peter Stace (hydro logy), Andrew Telfer, Nick Wat kins, Steve Barnett, Zac Sibernaler and Dave Clar ke (hyd rogeo logy), Ed Collingham (geotechnical) , Grant Lewis and Lance Gladigau (planning), Ken Ridley a nd Tom Wos ni ak (h ydra uli cs ) , Dave Kerry (pipelines), Jim Giffo rd and Ro d Wood (estimating), Greg Moore (materials), Rob Burnell and Biran Little (construction) and Peter Forward (operations), together with numerous patient d raughtsmen . Members of the Salt Interception Wo rking Grou p of the Murray Darling Basin Commissio n prov id ed o ngo ing peer rev iew of t he investigation and design process.