STRETCH OF THE RIVER MURRAY 5.5.1 The study area

The section of the River M urray used to te st the solute tran sp o rt model is the 207 km reach from E uston to Redcliffs. The location of th is reach and o th er geographical fea tu res associated w ith th e R iver M u rray and its

trib u ta rie s are show n in Figure 4.1 in C h ap ter 4. D uring in -bank flows, which is th e flow regime considered here, th e w ater level in th e lower p a rt of the study reach is influenced by the height of th e weirpool form ed behind th e w eir a t M ildura. This w eir, as for m ost o th er w eirs, serves both to reg u la te w a te r flow along th e R iver M u rray an d its trib u ta rie s an d to provide a pool from which irrigators can extract w ater for th e ir crops.

The land use m ap of the study area presented in Figure 5.1 shows large areas of irrig ated agriculture occur a t both ends of the study reach in close proxim ity to the river.

Figure 5.1 Land use map of the study area.

These a re a s are Euston-R obinvale and M ildura-R edcliffs. The la tte r forms p a rt of the Sunraysia - an extensive region of irrig ated agriculture in n o rth w e stern V ictoria. W ith in th e stu d y a re a , sm a lle r p ockets of irrig a tio n occur alongside th e riv e r in th e s tre tc h from Redcliffs to Colignan. A p a rt from irrig atio n -d ep en d en t a g ric u ltu re, th e o th e r m ain ag ricu ltu ral activities in the region are forestry and dry land farm ing for

cereal crops an d sheep grazing. A n u m b er of fo rests m an ag ed by th e respective sta te forestry departm ents are situ ated adjacent to th e river. In to ta l th ey com m and approxim ately one th ird of all available b a n k space along th e stu d y reach. In addition, the H attah -K u lk y n e N atio n al P a rk ab u ts the river south of Colignan in Victoria.

The above contrast in land use betw een irrig ated agriculture on the one h a n d , an d fo restry an d dry lan d farm in g on th e o th er, ex ists in p a rt b e c a u se a r e g u la te d riv e r flow s la n g u id ly th ro u g h a s e m i-a rid environm ent w here the m ean an n u al rainfall is approxim ately 300 mm.

B oth hydrological a n d hydrogeological d a ta a re re q u ire d for th e development of the solute tran sp o rt model. The hydrological d a ta employed in th is study were supplied by the M urray-D arling B asin Commission. The New South W ales D ep artm en t of W ater Resources and th e R u ral W ater Commission of V ictoria both supplied hydrogeological d a ta for th e study. The frequency of m easurem ent of these d a ta and a tte n d a n t ram ifications to model developm ent are next discussed.

5.5.2 The river flow and salinity data

For th e stu d y reach, the following hydrological d a ta w ere available: discharge a t E uston and Colignan; upper pool level a t M ildura weir; and river salinity a t E uston and Redcliffs (see Figure 4.7 in C h ap ter 4). S tream stage h eig h t a t C olignan and u p p er pool level d a ta a t M ild u ra w eir are m easured daily an d therefore constitute complete d a ta sets. In constrast, daily m easu rem en ts of riv er salin ity are not alw ays available. M issing e n trie s in th e d aily sa lin ity records have been e s tim a te d by lin e a r interpolation. Obviously, these composite daily salin ity d a ta sets contain in a c c u ra c ie s d u e to th e h ig h in cid en ce of d a y s w h e n s a lin ity m easurem ents have not been m ade. In illustration, Figure 5.2 p resen ts the composite daily sa lin ity d a ta a t E u sto n and Redcliffs for 1979. In th is figure, th e peak recorded dow nstream a t Redcliffs d u rin g late J a n u a ry is not recorded u p stre am in the E uston salin ity d a ta due to a period when m e a su re m e n ts w en t unrecorded. F u rth e rm o re , d u rin g th e sam e y ear th ere were extensive periods in M arch an d A pril w hen no salin ity d a ta were recorded a t eith er site.

downstream salinity

upstream salinity

discharge

JAN I FEB| MAR | APR i MAY | JUN | JUL | AUG | SEP | OCT | NOV | DEC

TIME (MONTHS) 1979

Figure 5.2 Composite daily salinity data upstream at Euston (continuous) and downstream at Redcliffs (dash) for 1979.

5.5.3 The groundwater data

Geological evidence in d icates th a t th ro u g h o u t th e stu d y a re a , th e P arilla Sand aquifer is the sole aquifer hydraulically connected to the River M urray (Lawrence, 1975; Brown and Stephenson, 1986).

Figure 5.3 m aps the location of observation bores in th e stu d y area. From th is m ap it can be seen th a t th e observation bores are unevenly d istrib u ted th ro u g h o u t the study area. Of all observation bores, 7059 and 7467 are num bered because, as detailed below, th e ir piezom etric h ead d a ta are used in the solute tran sp o rt model.

Piezom etric an d salin ity m easurem ents of th e P a rilla Sand aquifer in th e study a re a commenced in about m id 1960 w hen a sm all n u m b er of observation bores w ere su n k . Since th en , a d d itio n al bores h av e been positioned w ith th e m ajority in the period from the late 1970s to th e early 1980s. Even though there are a considerable num ber of observation bores in the study area, piezometric m easurem ents a t individual bores vary in th e ir frequency from two weeks to two years or more and often th ere are large gaps in piezom etric records. The m ore freq u en tly recorded piezom etric d a ta exist for observation bores located in the lower end of the study reach. Salinity m easu rem en ts of th e P a rilla Sand aquifer are m ade on a m uch less fre q u e n t an d re g u la r b a sis w ith two y e a rs ty p ically b ein g th e m inim um frequency of observation. Therefore, piezom etric an d salin ity m aps of the P a rilla Sand aquifer should be viewed w ith th is knowledge of

th e ir d a ta bases in mind.

LOCATION MAP OF OBSERVATION BORES