DEPARTMENT OF INFRASTRUCTURE PLANNING AND ENVIRONMENTNATURAL SYSTEMS DIVISION

Katherine Flooding,2003 / 2004 Wet Season

REPORT 11/2004DLakshman Rajaratnam, Steven J.Tickell & Roger FarrowDarwinApril 2004

Cover Photo: Uralla Rd flooding, view to the north east, 27/2/2004. Photo 9602.jpg,Gordon Atkinson, DIPE Katherine

Summary

Introduction

Observations

RainfallKatherine River Levels and FloodwayTindal CreekLot 1114 - Bicentennial Drive / Victoria Hwy.Uralla Rd

Discussion

Katherine Floodplain ModellingLot 1114 - Bicentennial Drive / Victoria Hwy.Uralla Rd

Conclusions

Lot 1114 - Bicentennial Drive / Victoria Hwy.Uralla Rd

Recommendations

Lot 1114 - Bicentennial Drive / Victoria Hwy.Uralla Rd

References

Glossary

Appendicies

1. Water level observations from various sources2. Flood extent and estimated water levels

Figures

1. Locality Map2. Daily rainfalls at Tindal and Katherine, 1 December 2003 to 22 March 20043. Longitudinal Section of Tindal Creek4. Daily rainfalls and water levels from G81404075. Katherine flood depth and extent – pre railway6. Katherine flood depth and extent – post railway7. Bore water levels from selected observation bores between Katherine and Tindal

RAAF Base.8. Bore water levels and Katherine annual rainfall.9. Daily rainfall at Tindal DR014932 and average daily water level in bore

RN02942910. Groundwater level contours (height above sea level) on 3/3/2004

Plates

1. Tindal Creek floodplain south west of Katherine East industrial area2. Tindal Creek floodplain downstream of G81404073. Tindal Creek floodplain and Drain 2 on the eastern side of Bicentennial Dve.4. Drain 2 near Walpiri Camp on the western side of Bicentennial Dve.5. Tindal Creek at the Victoria Hwy.6. Drain 2 at Bicentennial Dve.7. Tindal Creek at Uralla Road8. Tindal Creek floodplain at Stuart Hwy.9. Drain 1 behind the Katherine East industrial area10. Drain 2 near Walpiri Camp on the western side of Bicentennial Dve.11. Drain 3 at Bicentennial Dve.12. Tindal Creek at Victoria Hwy.13. Tindal floodplain just south and south east of Lot 298014. Lot 1114 Bicentennial Dve.15. Victoria Hwy at north side of railway overpass16. Victoria Hwy just north of the railway overpass.17. Novis Quarry road.18. Water seeping from the base of low limestone hills

Tables

1. Floodwater levels at a temporary gauge board on Uralla Rd2. Monthly Rainfalls (mm) for Katherine Railway Bridge, Katherine Museum and

Tindal AWS, 1st October 2003 to 31st March 20043. Daily rainfalls (mm) for Tindal AWS and Katherine Railway Bridge (old),

December 2003 to April 20044. Flood levels and Peak Flood Heights

Summary

The Katherine region and in particular the Tindal Creek catchment experienced wellabove average rainfall events during December 2003, February and March of 2004.The direct cause of the flooding was the several high daily rainfall events starting withthe highest event on the 23rd December. The situation was worsened by the fact thatthe underlying limestone aquifer filled to overflowing in many areas. This has neverbeen recorded before. In an average rainfall year a substantial proportion of rainfalldrains directly underground via sinkholes, caves and fractures in the rock. Aboveaverage rainfalls since the 1996/1997 wet season have raised regional watertables totheir present high levels. Runoff has increased substantially this season because thehigh watertable has blocked downward drainage to the aquifer. Clearing, urbanisationand drain construction in the catchment have also added to increased runoff. Theconveyance of the drainage system in Tindal Creek could not cope with this increasedrunoff and flooding occurred on both sides of Bicentennial Drive.

Another consequence of the high rainfall was the widespread discharge ofgroundwater to the surface via seepage areas and sinkholes within the Tindal Creekcatchment. A small lake formed along Uralla Rd. where an enclosed depression filledwith groundwater discharging from adjacent areas and with surface runoff. Thedepression would need to be drained to Tindal Creek to avoid the same problem infuture above average wet seasons. Complete draining will involve major works. Theother option is partial draining through the existing drain and allowing the remainingwater to decline naturally.

The flooding in Tindal Creek, the groundwater discharge and the lake along UrallaRoad are all likely to recur in future wet seasons if rainfall continues to be aboveaverage. Once groundwater levels have been raised it takes several years of average orbelow average rainfall for them to return to lower levels.

The flooding of the premises in the corner of Bicentennial Drive and VictoriaHighway (Lot 1114) is likely due to the flooding of Tindal Creek drainage system andpossibly the main drains in town as well. The flooding resulted from the exceptionalrainfall allied with increased runoff in an inefficient drainage system with awaterlogged floodplain and very high water table.

This report presents observations and analysis of the recent flooding.

Introduction

Localised flooding occurred in and around Katherine on several occasions fromDecember 2003 through to late February 2004. Lakshman Rajaratnam, Steven Tickelland Danuta Karp made a field inspection of the area on Monday 1st and Tuesday 2nd

March at the request of Northern Territory Emergency Services (NTES) andDepartment of Infrastructure and Planning (DIPE) staff in Katherine. The aim was todetermine the cause of the flooding in Lot 1114 and in some lots along Uralla Road.

Actions that could be considered to reduce future occurrences of flooding were alsoexamined.

Two sites were inspected; Uralla Rd, 5km south east of Katherine and a property onthe southern edge of Katherine at the intersection of the Victoria Highway andBicentennial Drive (Figure 1). The latter is Lot 1114 on which the business “HobbitAuto Electrics” is located. On Uralla Rd. three properties were badly effected, NTportions 2142, 2143 and 2144. Two helicopter flights were made to determine theextent of floodwaters, one on Friday 27/3/2004 by Gordon Atkinson (DIPE,Katherine) and another on Monday 1/3/2004. Photographic records were made oneach flight.

Roger Farrow and Paul Schober conducted a regular run of bore waterlevelmeasurements later that week. They also installed two gauge boards to record the riseand fall of flood heights. They gauged the outflow of water across Uralla Rd whereverit was possible, and flow in the new cut drain. They also surveyed the peak floodheights, the invert of the culvert, and took photographs of flooding in properties,roads, and road crossings (Appendix 1). Mr Bernie Tomlin of Uralla Road has beenrecording the gauge heights and the local rainfall (Table 1).

The three main drains that run from the Katherine urban area to the Tindal Creek arereferred to below as “Drains 1, 2 and 3” (see Figure 1 for their locations).

Observations

RainfallIn the last six years the total annual rainfall in the region has generally been aboveaverage. The current wet season has seen exceptional falls. At the old KatherineRailway Bridge (operated by DIPE), Tindal AWS (Automatic Weather Stationoperated by CBM) and Katherine Museum (Operated by CBM) rainfall totals fromOctober to end of March were 1603mm, 2144 mm and 1569 mm respectively (Table2), well above the respective annual averages of 912mm, 1099 mm and 1077mm.Daily rainfalls for these stations from December 2003 to April 2004 are listed inTable 3. It should be noted that the daily rainfalls in this report are 24-hour rainfalls to9 am on that day. The Darwin Regional office of the Commonwealth Bureau ofMeteorology supplied all rainfall data and statistics.

The one-day total of 284mm at Tindal on the 22nd December 2003 is higher than anydaily rainfall recorded at Katherine in the past 132 years. The two day rainfall total atTindal on the 22nd and 23rd of December 2003 was 392mm. Katherine Railway Bridgerecorded 93mm on 22nd and 199mm on 23rd of December 2003. Figure 2 comparesdaily rainfalls at Tindal and the Katherine Railway Bridge.

Katherine River Levels and FloodwayThe maximum river level reached at the old Katherine Railway Bridge so far for thisWet season is 16.2m GH (Gauge Height) in December 2003. The highest levelsrecorded at the old bridge in February and March 2004 were 13.0 and 15.0m GHrespectively. These are still below the level when Katherine River breaks its bank ataround 17.0m GH.

The original designated flood level (1% Annual Exceedance Probablity – literallymeaning 1 in 100 year flood) at the Old Railway Bridge was 19.27m GH which is105.63m AHD (Australian Height Datum). The designated flood level was revisedafter the 1998 floods (Water Studies Pty Ltd, 2000) to 19.98 m GH (106.34 m AHD).The 5% AEP (1 in 20 year) flood level at the old bridge is 18.86m GH. Areas withmore than 2m depth of flood are referred to as “floodway” (Water Studies, 1998). Theold and the new designated flood levels in Lot 1114 are 104.0m and 105.2m AHDrespectively. Lot 1114 was in the Floodway as per the old designated flood level andhence it is also in the floodway as per the new designated flood level.

Tindal CreekThe creek rises in an area some 20km south of the Tindal RAAF Base. It flows northwest to the Stuart Highway where it changes direction abruptly to the west-southwest.Downstream of the highway it has a floodplain that averages 1km in width. Itschannel is poorly defined in this area. Several drains from urban areas to the northjoin the creek between the Stuart and Victoria Highways. Near the intersection ofBicentennial Dve. and the Victoria Hwy. the floodplain abruptly narrows to 300metres between a bedrock hill to the east and the levee bank of the Katherine River tothe west. From that point the creek turns to the southwest and is joined by severaltributaries coming from the southeast. Downstream of the old Victoria Highway itbecomes progressively more entrenched and meandering until it reaches the KatherineRiver.

An approximate longitudinal section of the Tindal Creek from Uralla Road to theconfluence of Katherine River (derived from Photo-Image Map of Katherine 1998) isshown in Figure 3. The catchment areas at the first Stuart Highway crossing, thesecond Stuart Highway crossing and at the Victoria Highway are 334, 353 and 397km2 respectively. The catchment of the tributaries flowing into Tindal Creekdownstream of the Victoria Highway is 119 km2. Approximate ground slopes ofTindal Creek were estimated using the 1m contours from the Photo-Image Map ofKatherine (1:5000) scale. The section between the recorder (G8140407) and thecrossing at the Victoria Highway has a moderate slope of 0.0015. The sectionbetween the crossing at Victoria Highway and the crossing at the old VictoriaHighway has a slope of 0.0012. The section between the old Victoria HighwayCrossing and the last tributary confluence has a slope of 0.0016. The slopes arecommonly up to a one and a half metre drop over a kilometre.

Lot 1114 - Bicentennial Drive / Victoria HighwayHobbit Auto Electrics in Lot 1114, which is located on the corner of BicentennialDrive and Victoria Highway, was visited by Lakshman Rajaratnam (DIPE, Darwin),Gordon Atkinson (DIPE, Katherine) and Warrick Jacks (Katherine Town Council) onthe 2nd March 2004. The owner, David Bretherton was present and he described theflooding of his property, which he stated had occurred four times this wet season. Thefirst flood was on the 23rd of December 2003 with subsequent occurrences on the 22nd

and 28th of February 2004 and on the 3rd of March 2004. On the last occasion theoffice flooded to a maximum height of 0.6m (above floor level). David marked theflood heights and DIPE agreed to install a gauge plate in the vicinity of the lot. Thiswas done the next day. According to the owner, the water was flowing from southeast

to northwest across Bicentennial Drive into his lot during all these events. In the lastflood, water was seen backing up northeast along the town drain east of the VictoriaHighway and was overflowing the highway on to the northwestern side.

Mr. Bretherton expressed concerns over the inadequate drainage in the Tindal Creekbeing the cause of the flooding. He feels that the Tindal Creek flood ponds on theeastern side of Bicentennial Drive and flows through the culvert at the corner ofBicentennial Drive and the Victoria Highway (culvert A) and then over the road intothe lot. He agreed that the December flood extent was consistent with the 1 in 100year modelling that was done for DIPE by the consultants. However, he feels that thesubsequent flooding would have been avoided if man made obstructions wereremoved from Tindal Creek. Possible restrictions to flow along the Tindal Creek werediscussed, including the railway haulage road and Tindal Creek crossings of the newand old Victoria Highways. During the inspection Tindal Creek was over-flowing theold Victoria Highway by about 100mm. Another tributary of Tindal crossing NovisQuarry Road was also overflowing.

The location of the two height recorders G8140407 and G1840408 in relation to Lot1114 are shown on Figure 1. The recorders are designed to measure water levelscontinuously. G8140407 was functioning but G8140408 was not. Appendix 1contains water level observations from the following locations: G8140407, shed inHobbits Auto Electrics (manual readings), the gauge plate on a tree close toG8140408, and from selected monitoring bores. It also has the invert levels of theopenings in culvert A. Flood levels and peak flood heights are noted in Table 4. Aplot of daily rainfalls recorded at the old Katherine Railway Bridge, KatherineAviation Museum, and Tindal AWS along with the water level from G8140407 isshown in Figure 4.

Aerial photographs taken on the 27/02/2004 and 01/03/2004 as well as ground levelphotographs taken on 3/03/2004 were used to assess the flood extent (Appendix 2).The extent of flooding in the photograph was compared with the 1m contours on the1:5000 photo-image map of Katherine (1998). A first pass estimate of the floodextent, flood slope and the water levels was also noted.

Uralla RoadA shallow lake of some 97 hectares extends over several properties, mainly on theeast side of the road (see cover photograph). Access along the road was blocked andsome houses were flooded by up to 1.0 m of water. The lake first started to form somefour weeks previously (Bernie Tomlin) and was at a level of 109.66m AHD on2/3/2004.

A 500 metre long drain was dug from the west side of the road towards the TindalCreek during late February. The rectangular drain was approximately 0.6m wide and0.75 m deep. Its flow was gauged at 56 litres/second on 03/03/2004. Where the lakecrosses Uralla Road, flow was only detected at its northern end and was measured at750 litres/second on the same day. That latter water sheet flowed over a wide area toTindal Creek. The drain was enlarged and its flow on 17/3/2004 was 837litres/second. At that latter date the majority of flow out of the lake was via the drain.

Some basic water quality parameters were measured, in order to determine the sourceof the water. On 2/3/2004, along the road outside of NT portion 2142, electricalconductivity was 349 µS/cm; pH 7.35 and temperature 28.20C. On the 17/3/2004 theelectrical conductivity of water in the drain was 500 µS/cm.

The lake is located in a natural closed depression in a minor tributary valley of theTindal Creek. There is normally no significant surfacewater flow in the valley. Runoffnormally drains into sinkholes (Karp 2002), fractures and cavities in limestoneoutcrops that surround the valley. The Tindal Limestone, an important cavernous andfractured rock aquifer, underlies the area. The local residents reported water issuingfrom springs at the base of the hills. Abundant springs and broad areas of seepagewere seen along Collins and Cragborn roads, just to the east and north east of the lake.A Water Resources observation bore RN022394, located at the southern end of UrallaRd. had a water level of 109.54 metres AHD on 3/3/2004, similar to that of the lakelevel (109.66m) on the previous day. A further level of 108.83 metres AHD wasrecorded on the 16/3/2004. The lake level was 109.43m on that day. The watertabledropped 0.71m while the lake only dropped by 0.23m over that period.

Discussion

The local floods in Katherine have taken some residents by surprise, flooding somewho were not affected by the major Katherine riverine flooding of 1998. Others whowere within the 1 in 100 year flood extent were flooded despite the river not breakingits banks. The areas affected include rural blocks on Uralla Rd, the workshop on thecorner of Bicentennial Drive and the Victoria Highway in Lot 1114, and parts of theVictoria Highway, Harrod Street, Rundle Street and other streets in that vicinity.

Katherine Floodplain ModellingFloodplain modelling of Katherine River was undertaken for DIPE by consultants(Water Studies Pty Ltd, 2000). This estimated floodplain inundation, peak floodheights, and flood extents for Katherine from the Katherine Gorge to Vampire Creek.Flood maps incorporating peak flood heights, flood extents, and floodway for 1%,2%, and 5% AEP flood events were produced. In December 1999, a report wasproduced by the same consultants regarding the impact of the railway embankment onthe 1% AEP flood extent and inundation. The design of the railway embankment andthe openings (bridges and viaducts) was done with the objective of minimum impacton the Katherine Designated Flood Level (Coffey Water Studies, 1999). Sufficientopenings have been allowed to keep the afflux (additional height above the normalheight) in high-risk areas (town area) to a minimum. Immediate surroundings (low orno risk areas) just upstream of the embankments will bear the maximum afflux of theorder of 0.25m. There is no afflux over the Designated Flood Levels elsewhereincluding the Katherine CBD area. Flood depth ranges and extent around BicentennialDrive due to a 1 in 100-year rainfall over the entire catchment when the river level is17.5m at the old Railway Bridge are shown in Figure 5 and 6. Figure 6 shows the postrailway line situation while Figure 5 shows the situation before the construction of therailway.

Lot 1114 - Bicentennial Drive / Victoria HighwayEach major rainfall event and the subsequent flooding as well as the impact on Lot1114 are discussed below. Flood level interpretations from the aerial photographstaken on the 27th of February and 1st of March 2004 are also discussed.

22nd and 23rd December 2003The first flooding of Lot 1114 was on December 23rd and followed very high rainfallin the Tindal catchment that flooded Tindal Creek. The floodplain modellingdescribed above clearly shows that the flood in the subject lot was not due to theKatherine River overflowing its banks. The owner said that there was inundation of0.75 m to 1m and this is consistent with the model predictions.

The modelled flood depth ranges in Lot 1114 (Figure 5 and 6) clearly show that theimpact of railway was minimal. This was evidenced by the fact that the level of theTindal Creek was well below the railway viaduct during the flooding on the 27/02/03(photo 9682).

The one day rainfall at Tindal, Katherine Museum and Katherine Railway up to 9amon the 23rd was estimated to be between 1 in 100 and 1 in 200 years, about 1 in 25years, and 1 in 20 years respectively. The overall one-day rainfall in Tindal catchmentand Katherine town area was less than 1 in 100-year event. The peak flood level thatwas observed at the Lot 1114 (102.83m AHD at 03:00hours on 23rd) which was lessthan that noted in Figures 5 and 6 is consistent with the exceptional rainfall. Duringthis event, the peak level recorded at the Katherine Old Railway Bridge was 16.16mGH at 06:00 hours on the 23rd. At this height the river does not break its bank aroundthe town area. The flooding was due to the runoff from the town and Tindal Creekcatchment.

The Katherine Flood Model indicates a level of 99.7m AHD at the confluence ofTindal Creek and Katherine River for a 1 in 100-year rainfall over the catchmentwhen the river level at the old bridge is 17.5m GH and rising. The peak as notedbefore was 16.16m GH and hence an estimate of the river level at the confluence islikely to be less than 98.2 m AHD. If the river level at the confluence is 98.0m AHD,the river level would back up along Tindal Creek to the old Victoria Highway.However during this event the level at the confluence would be less than 98.0m AHD,as the overall rainfall has been less than 1 in 100-year event.

28th and 29th January 2004Katherine Railway Bridge and Tindal recorded a 24-hour rainfall of 65 and 21mmrespectively up to 9 am on the 28th. The 24-hour rainfall up to 9 am on the 29th, atKatherine Museum was 103mm and at Tindal 56mm. The river at Katherine OldRailway Bridge peaked at 10.43m GH at 01:45 hours on the 29th. The height recorderG8140407 indicated a flood peak of 101.42m at 13:15 hours on 28th and is likely dueto the town rainfall on 27th and 28th. There may have been another flood peak on the29th. However, height records are not available for this recorder from 29th of Januaryto 9th of February 2004. It seems that the flood peak height was not high enough toinundate Lot 1114.

During this event a first pass estimate of the peak level at the Katherine River / TindalCreek confluence would be less than 92.0 m AHD. If the river level at the confluenceis 92.0m AHD, the river would back up along Tindal Creek to a distance of less than300m which should not have caused any obstruction to the flow down Tindal Creek.Also Tindal experienced less rainfall than Katherine Town area. Therefore the waterlevels on both sides of Bicentennial Drive were not sufficient to inundate Lot 1114.

16th and 17th February 2004There was very little rain recorded at Katherine Railway Bridge and the Museum overthe 48 hours up to 9 am on the 16th. Tindal recorded 42 and 92 mm up to 9 am on the15th and 16th respectively. The height recorder G8140407 indicated a flood peak of101.8m AHD on 17/02/04 at 08:00 hours. The river height at the Katherine OldRailway Bridge was 6.92m GH at 23:15 hours on the 16th and still rising. The riverlevel at the confluence would be too low to have any impact on the Tindal floodplainwater levels. It is very likely that one of the major factors causing this flooding is thehigh two-day rainfall in Tindal catchment. There would have been little or noinundation of Lot 1114 and the buildings were not inundated.

22nd and 23rd February 2004There was little rain in the Katherine Town area while the Katherine Museum andTindal recorded 48 and 128 mm up to 9am of the 22nd respectively. Again Tindalrecorded 44mm up to 9am of the 23rd. Lot 1114 was inundated and according to theowner, water level reached the floor. A peak flood height of 102.56m was reached onLot 1114 on the 23rd at 04:00 hours. The height recorder G8140407 indicated a floodpeak of 102.35m AHD on the 23rd at 01:12 hours. It is very likely that the majorfactor causing this flooding is the high two-day rainfall in Tindal catchment. There isa difference between the peak height observed in Lot 1114 and that of the heightrecorder. This could be attributed to the water surface slope. However the time offlood peak height observed at Lot 1114 and the height recorder are different and needsexplanation.

The peak river level recorded at the Katherine Railway Bridge was 11.07m GH on the23rd at 15:23 hours and should not have had an impact on the local flooding. Whenthis event occurred, it is presumed that there would have been water in the Tindalfloodplain, sourced from discharging groundwater. Significant flows from the majortributary of the creek near the confluence would have increased the water level nearthe confluence.

27th February 2004The water levels estimated from the aerial photographs are consistent with those fromthe height recorder on the evening of the 27th (101.3 to 101.4m AHD). The first passestimate of the level on the eastern side of the Bicentennial Drive was about 101.5mAHD across Lot 1114. Since the river level was low (less than 92.0 m AHD) therewas flow in Tindal Creek downstream of the new Railway Bridge as seen onphotograph 9682. A first pass estimate of the water surface slope indicate that it is lessthan the respective ground slope between the height recorder (G8140407) and theVictoria Highway Crossing. This would indicate that the flow is not free and may bedue to insufficient drainage capacity.

Water in Tindal floodplain being sustained at these levels since the last flood eventfour days previously, would mean that there was continuous flow from groundwaterdischarging from springs and sinkholes adjacent to the floodplain.

28th February 2004Katherine Museum and Tindal recorded about 75mm up to 9 am of 28th whileKatherine Railway Bridge recorded 38mm over the same period. Lot 1114 wasflooded and the building was 100mm under water at the peak. The peak flood heightas observed by the owner was 102.66m AHD at 22:00 hours on the 28th. The peakheight recorded by the height recorder was 102.46m AHD at 02:24 hours on the 29th.The difference between the peak heights could be attributed to the water surfaceslope. However, the difference between the times of the flood peak height needsexplanation.

The peak river level recorded at the Katherine Old Railway Bridge was 13.0m GH onthe 28th at midnight. This peak was due to the rainfalls upstream of Katherine Townarea. Though the peak river level at the confluence would have backed into TindalCreek, the impact on the local flooding would be insignificant. When this eventoccurred, there was already water ponded in the floodplain and this is one of thereasons for the inundation of Lot 1114. A secondary reason being groundwatertopping up the ponded water despite evaporation and transpiration. Significant flowsfrom the two tributaries of the creek near the confluence would have increased thewater level near the confluence.

1st March 2004The water levels estimated from the aerial photographs are not consistent with thosefrom the height recorder on the evening of the 1st. At that time the height recorderindicated a level of 101.6 to 101.7m AHD but a first pass estimate of the level on theeastern side of the Bicentennial Drive was about 101.3m AHD across Lot 1114. Thisdiscrepancy needs to be explained.

The water level in the river on the evening of the 1st was 10.5m and falling at the oldRailway Bridge. This would mean that the river level at the confluence was too low tohave any impact on the water ponding in the Tindal Creek floodplain. A first passestimate of the water surface slope as observed from the photographs taken in theevening indicate that it is slightly less than the respective ground slope between theheight recorder and the Victoria Highway Crossing. This would indicate that the flowis not free and may be due to insufficient drainage capacity.

Water in Tindal floodplain being sustained at these levels since the last flood eventthree days previously, would mean that there was continuous flow from groundwaterdischarging from springs and sinkholes adjacent to the floodplain.

3rd March 2004Tindal, Katherine Museum and Katherine Old Railway Bridge recorded 116, 75, and62 mm of rainfall respectively up to 9 am on the 3rd. This resulted in the inundation ofLot 1114 by about 0.6m. There was runoff from both sides of Bicentennial Drive, thetown area and the Tindal catchment. The peak flood height as observed by the ownerwas 103.16m AHD at 17:30 hours on the 3rd. The peak height recorded by the heightrecorder was 102.89m AHD at 18:32 hours on the 3rd and level at 17:30 hours was

102.88. The difference between the peak flood heights could be attributed to slope ofthe water surface and the timing of the peaks seems consistent.

The river level at Katherine peaked at noon on the 3rd at 15.04m GH at the oldRailway Bridge. This peak would have travelled to the confluence in the next hour. Afirst pass estimate of this flood wave peak at the confluence is likely to be less than97.0 m AHD. At the time of the flood peak in the premises around 17:30 hours, theriver height at the old Railway Bridge was 14.71m and falling. Therefore it is verylikely that the water level backing into Tindal Creek from the river would have someimpact on the flooding but not significant. When this event occurred, there wasalready water ponded in the floodplain and this may also have contributed to theinundation. The other factor contributing to the inundation was groundwater toppingup the ponded water on the floodplain. The water table may have been above groundlevel on either side of Bicentennial Drive. The monitoring bore (RN22475) near theWalpiri Camp entrance in Bicentennial Drive was overflowing on the 5th of March,indicating that the water table was above the ground level on this day.

Significant flows from the two tributaries of the creek near the confluence would haveincreased the water level near the confluence. The DIPE field crew noted the waterlevel in this creek at noon on the 3rd was over Novis Quarry Road. At the same timeTindal Creek was overflowing the old Victoria Highway bridge and lapping onto thecurrent Victoria Highway bridge. Tindal Creek just upstream of the Stuart Highway.peaked around 10:30 hours. There is a seven-hour lag between the peak at StuartHighway and that at the recorder. The peak flow from Tindal Creek should havereached height recorder sooner than the 7-hour lag.

A first pass estimate of the water surface slopes along different sections of the creekas observed from the photographs taken just before noon indicate that they are similarto the respective ground slopes. This would indicate that there is free flow in thecreek.

Each time Tindal Creek was overflowing Uralla Road it filled the floodplain south ofthe industrial area and east of Bicentennial Drive. In essence the floodplain acts as aretention basin. Water backs up during a major rainfall event because of the naturalrestriction at the downstream end of the floodplain (Figure 5). This wet season, thebasin has been replenished by groundwater discharging from the Tindal Limestoneaquifer. In this fully saturated environment, any heavy rainfalls in the catchmentdirectly translate into runoff and thus flooding. In a flash flood situation draining thewater from both sides of Bicentennial Drive as quick as possible will increase theflooding immunity for Lot 1114 area. This may be partly possible by improving thecapacity of Tindal Creek to the Katherine River.

Any alteration to the Tindal Creek drainage such as additional inflow through newdrain construction as well as clearing and urbanisation in the catchment will alsoincrease runoff. Improving the drainage in one part will have impact elsewhere in thefloodplain. However only a proper hydrological and a hydraulics study of the areaconcerned will be able to deliver the appropriate improvements in drainage with leastenvironmental damage. One of the cost-effective measures to mitigate flood hazardsis to restrict development in a designated floodway.

Uralla RdThe groundwater levels in the Tindal aquifer are currently at an all time high sincemeasurements began in the mid 1980’s (Figure 7). The reason for this is the run ofabove average annual rainfalls since the 1996/1997 wet season (Figure 8). Thedetailed response of groundwater levels to rainfall is shown in Figure 9 where dailyrainfalls at Tindal are plotted with the hydrograph of the observation bore RN029429.In late December the watertable rose by 3.5 metres over twelve days due mainly toheavy rainfalls on the 22nd, 23rd and 31st of December 2003. From January to mid-March an additional rise of only 1.5 metres occurred despite significant rainfalls. Theaquifer filled to overflowing and so was unable to accept more recharge.

In February and March the watertable was close to or even above ground level in low-lying areas. This means that there was no longer an avenue for surface runoff to draindown into the aquifer. In previous years a high proportion of runoff soaked into theground or drained directly into sinkholes or caves. The depression along Uralla Rdusually did not hold water because it lost water through downward drainage fasterthan it ran in. A lake formed this season because the runoff had nowhere to drain. Thesource of the lake water was a combination of groundwater, rain falling directly onthe lake and surface runoff from higher in the catchment. The groundwater comesfrom springs and sinkholes higher in the catchment and presumably from similarfeatures under and surrounding the lake. A similar feature locally known as “LakeHickey” formed several years ago just west of Katherine, adjacent to Zimmin Dve.That has filled intermittently since 1998 and takes up to several months to dry. It isdirectly connected to the watertable by caves and sinkholes. In March this year thelake was discharging some 3000 Litres/second through a recently constructed drain.

The contribution from groundwater can be seen in the high electrical conductivity ofthe lake water (349 µS/cm). Electrical conductivity gives a measure of the amount ofsalts dissolved in water. Rainwater would typically be less than 30 µS/cm while thelocal groundwater averages 600 µS/cm. More than half of the lake water musttherefore be sourced from groundwater.

The extent of groundwater discharge to the surface can be gauged by the height of thewatertable across the area (Figure 10). Areas likely to be sites of seepage or springsare where the watertable is above ground level and where there is no sealing layersuch as thick clay soil. On the aerial inspection, groundwater was observeddischarging over a wide area from the Tindal RAAF Base to Katherine. The mainsites were at the base of rocky hills where they adjoin valleys with alluvium or soilcover (Plate 18).

Inflow of water to the lake will continue until groundwater levels in the seepage areasdrop below ground level. On the 16th March the watertable had dropped to 0.6 metresbelow the lake level suggesting that there is little direct connection between the lakeand the watertable. The base of the lake is probably sealed by soil and so once thelake has been lowered to the level of the intake of the new drain, water will only belost by evaporation (approximately 6mm/day). The lake is likely to remain for severalmore months and if similar high rainfalls occur next season the problem will recur.

Plate 18 Water seeping from the base of low limestone hills, NT por. 5591, view tothe northeast. Photo Gordon Atkinson, DIPE Katherine, 27/2/2004.

A more immediate and permanent solution to the flooding experienced on UrallaRoad is the construction of a drain. This would facilitate the draw-down of the lake tothe minimum level of Uralla Road. A small drain was constructed during the lastweek of February and was enlarged between the 8th and 15th of March. The base of thedrain at the start should be above 108.5 m AHD; otherwise the channel would tend todrain the sinkhole rather than the water in the inundated areas in Uralla Road. Thedrain should slope down to the natural surface of 105.0m AHD over a distance of akilometre.

The drain should have a bed width of at least 2m and a side slope of 1 in 2 for drainstability. Assuming an overall slope of 0.003 with a bed roughness of naturallyexcavated material (Mannings number of approximately 0.035), the design dischargeof the drain for a flow depth of 1m is about 4500 litres/second. The existing drain isrectangular in section with a width of 3.2m and a depth of 1m. Its flow measured atthe upstream end was 837 Litres/second on 17.03.04. The flow measured in theoriginal drain, which was smaller (0.6m wide and 0.7m deep), was 56 Litres/secondon 03/03/04. At the rate of 840 Litres/second, it would take 6 days to discharge 450Ml. However there is groundwater flow into the lake.

To install a permanent feature to drain the ponded water below the level of the road inLot 2143 and neighbouring properties would need a detailed survey of the area. Theestablished ground levels could then be used to design an underground drainage pipesystem to discharge the ponded water into the nearest low-lying area across the road.

Conclusions

Lot 1114 - Bicentennial Drive / Victoria Hwy.The flooding of Lot 1114 was due to the following factors:• Heavy rainfall over short periods.• Low conveyance of Tindal Creek due to inefficient drainage to the Katherine

River.The situation was exacerbated by:• A high watertable keeping the floodplain waterlogged.• A natural water way restriction (Figure 5) resulting in water backing up onto the

floodplain.• Water levels in Katherine River backing into Tindal Creek during major rainfall

events as in the first and the last event. This however had minimal impact on theflood levels on the Tindal floodplain.

Uralla Rd.The lake on the Uralla Rd. properties resulted from a combination of several factors.Above average rainfalls since the 1996/1997 have raised watertables to high levels.The rainfall in the 2003/2004 wet season has been exceptional and filled the aquifer tooverflowing in many areas. This resulted in widespread springs and seepages in areaswhere such features have never been noted before. The high watertables have meantthat nearly all of the rainfall has been diverted as surface runoff. Discharginggroundwater and surface runoff collected in a low enclosed depression to form thenew lake. Should the above average rainfalls continue next wet season the lake willlikely form again.

Recommendations

The following recommendations are made to minimise the flood hazard throughappropriate mitigation in the town and nearby rural areas.

Lot 1114 - Bicentennial Drive / Victoria Hwy.A hydrological and hydraulics study of the Tindal Creek catchment is required so thata design to increase sustainable drainage from the Tindal Creek Floodplain can beundertaken. Different options should be studied for cost and hydraulic effectiveness.

Uralla Road1. Maintain and improve the newly constructed drain.2. Additional Gauge Boards to be placed at strategic points to monitor future flood

level.3. Monitoring bores in the town and greater town area should be maintained.

In addition to the technical recommendations noted above serious consideration mustbe given to planning issues in areas within the designated flood extent. This wouldinvolve restricting development in a floodway.

References

Coffey Water Studies, 1999 Impact of Proposed Katherine River Crossings onUpstream Flood Levels – Report No 12/99D, Department of Transport & Works -Department of Lands, Planning & Environment.

Commonwealth Bureau of Meteorology (CBM) – Regional Office Darwin, Daily,Annual and Annual Average Rainfalls.

Karp, D. 2002 Land degradation associated with sinkhole development in theKatherine region, Department of Lands, Planning & Environment

Water Studies, 1998 Best Practice Guidelines – Floodplain Management in Australia,March 1998, Water Studies, QLD, Australia

Water Studies Pty Ltd, 2000.Katherine River Flood Study, Report 02/2000DDepartment of Lands, Planning & Environment

GlossaryAnnual Exceedance Probability (AEP): The likelihood of occurrence of a flood of agiven size or larger in any one year; usually expressed as a percentage.

Aquifer: A body of rock that is sufficiently permeable to conduct groundwater andyield economically significant quantities of water to bores or springs.

Australian Height Datum (AHD): Survey height datum adopted by the NationalMapping Council of Australia as the reference datum for defining reduced levels.

Designated Flood Level: The flood level that represents the 1% AEP flood event. 1%AEP flood event is selected as the defined flood event for the management of floodhazard as determined by the floodplain studies.

Floodway: Those areas of the floodplain where significant velocity or height of wateroccurs during a 1% AEP flood event. In the Northern Territory, any areas with 2m ormore of inundation for a 1% AEP flood or areas where the product of velocity andheight is more than 1 is defined as a floodway.

Runoff: The rainfall that falls in a catchment and drains into the surface drainage andbecomes a creek or stream flow.

Sinkhole: A funnel shaped depression caused by solution and or collapse ofunderlying limestone. Often directly connected to subterranean caverns.

Watertable: The water level in an unconfined aquifer.

Table 1 Floodwater levels at a temporary gauge board on Uralla Rd,opposite NT Por.2143. Observations made by Mr Bernie Tomlin.

Date Time Level(m) Level (m_AHD) Rainfall(mm) Comments2/03/2004 17:00 0.74 109.664 03/03/2004 ? ? ? 70 level rose

100mm4/03/2004 16:30 0.744 109.668 05/03/2004 16:15 0.734 109.658 06/03/2004 16:30 0.73 109.654 0 Same level as on

27/2/047/03/2004 16:15 0.715 109.639 08/03/2004 17:00 0.702 109.626 0 Diversion trench

started9/03/2004 16:30 0.695 109.619 010/03/2004 16:30 0.665 109.589 011/03/2004 16:15 0.685 109.609 11 up to 40mm rain

on eastern side12/03/2004 16:30 0.675 109.599 013/03/2004 16:30 0.663 109.587 814/03/2004 16:45 0.605 109.529 1015/03/2004 16:30 0.555 109.479 17 Diversion trench

finished16/03/2004 16:00 0.51 109.434 017/03/2004 8:00 0.524 109.448 24

Table 2 Monthly Rainfalls (mm) for Katherine Railway Bridge, Katherine Museumand Tindal AWS, 1st October 2003 to 31st March 2004

Months Katherine RailwayBridge

Katherine Museum Tindal AWS

Total Average Total Average Total AverageOctober 03 0 30.1 0 39.1 17.6 42.1November 03 36 93.8 0 88.7 39.4 102December 03 503.5 216.6 531 191.5 638.8 187January 04 332 262.8 301 270.6 356.8 268February 04 322 202.2 387 251.3 695.8 240March 04 409 106.6 350.4 182.7 396.0 147Total 1602.5 912.1 1569.4 1023.9 2144.4 986.1

Date TindallAWS

KatherineRailwayBridge

Date TindallAWS

KatherineRailwayBridge

Date TindalAWS

KatherineRailwayBridge

Date TindallAWS

KatherineRailwayBridge

1-Dec-03 0 0 1-Jan-04 0 23 1-Feb-04 0 0 1-Mar-042-Dec-03 13 0 2-Jan-04 37 16 2-Feb-04 0 0 2-Mar-04 7.4 23-Dec-03 0 0 3-Jan-04 0.4 0.5 3-Feb-04 7 0 3-Mar-04 116 624-Dec-03 0 0 4-Jan-04 0 0 4-Feb-04 45 37 4-Mar-04 0 2.55-Dec-03 0 0 5-Jan-04 0.4 11 5-Feb-04 0.2 0 5-Mar-04 1.2 7.56-Dec-03 0 0 6-Jan-04 8 17 6-Feb-04 21 21 6-Mar-04 0 07-Dec-03 5 0 7-Jan-04 0 0 7-Feb-04 37 11 7-Mar-04 0 08-Dec-03 0 0 8-Jan-04 13 3 8-Feb-04 68 8 8-Mar-04 0 09-Dec-03 0 2 9-Jan-04 4 1 9-Feb-04 27 37 9-Mar-04 0 0

10-Dec-03 0.2 3 10-Jan-04 14 21 10-Feb-04 34 27 10-Mar-04 0 011-Dec-03 0 0 11-Jan-04 38 21 11-Feb-04 0.4 0.5 11-Mar-04 5.6 2312-Dec-03 5 13 12-Jan-04 10 14 12-Feb-04 0.4 0 12-Mar-04 0 013-Dec-03 0 0 13-Jan-04 51 43 13-Feb-04 0 0 13-Mar-04 3 1014-Dec-03 32 0 14-Jan-04 22 16 14-Feb-04 2 1 14-Mar-04 8 115-Dec-03 3 7 15-Jan-04 0 2 15-Feb-04 42 11 15-Mar-04 0.6 016-Dec-03 - - 16-Jan-04 0 0 16-Feb-04 92 11 16-Mar-04 33 717-Dec-03 - - 17-Jan-04 0 0 17-Feb-04 4 31 17-Mar-04 28 2018-Dec-03 40 23 18-Jan-04 0 0 18-Feb-04 2 7 18-Mar-04 29 719-Dec-03 5 7 19-Jan-04 0 0 19-Feb-04 7 2 19-Mar-04 22 3220-Dec-03 0.4 0 20-Jan-04 0 0 20-Feb-04 0 0.5 20-Mar-04 29 4621-Dec-03 3 17 21-Jan-04 36 14 21-Feb-04 9 19 21-Mar-04 9.8 1822-Dec-03 108 93 22-Jan-04 20 0.5 22-Feb-04 128 12 22-Mar-04 43 5423-Dec-03 284 199 23-Jan-04 1 0.5 23-Feb-04 44 13 23-Mar-04 0 024-Dec-03 0.2 0.5 24-Jan-04 0.2 5 24-Feb-04 1 19 24-Mar-04 2 1825-Dec-03 21 8 25-Jan-04 3 0.5 25-Feb-04 6 0 25-Mar-04 0 026-Dec-03 15 8 26-Jan-04 1 29 26-Feb-04 17 2 26-Mar-04 6 827-Dec-03 0 0 27-Jan-04 11 5 27-Feb-04 21 14 27-Mar-04 53 2328-Dec-03 0 0 28-Jan-04 21 65 28-Feb-04 80 38 28-Mar-04 0 029-Dec-03 6 5 29-Jan-04 56 23 29-Feb-04 0 0 29-Mar-04 0 030-Dec-03 13 28 30-Jan-04 0 1 30-Mar-04 0 031-Dec-03 85 90 31-Jan-04 6 0 31-Mar-04 0 0

Table 3 Daily rainfall (24Hr rainfall readings in mm to 9am on the day listed) for Tindal AWS and Katherine Railway Bridge (old)

Table 4 Flood levels and Peak Flood Heights

Date 24 hrrainfallto 09:00at TindalAWS

Time ObservedInundationat Lot 1114above floorlevel (m)

Water levelof observedinundationat Lot 1114m AHD

ObservedLevel –Gaugeplate ontree

ObservedLevel -GaugeStationG8140408

ObservedLevel –GaugeStationG8140407

Water LevelboreRN 22475

Water LevelBoreRN 22397

Comments

22/12/03 10823/12/03 284 0.24 102.803 Flood Peak Lot 111413/01/04 51 No flooding Reported29/01/04 56 No flooding Reported15/02/04 42 No flooding Reported16/02/04 92 18:00 101.547 No flooding Reported17/02/04 06:41 101.80222/02/04 128 20:45 102.30523/02/04 44 01:12 102.354 Peak Level

04:00 0.0 102.563 Flooded up-to floorlevel; Flood Peak

17:47 102.26128/02/04 80 18:21 102.355

22:00 0.100 102.663 102.420 Flood Peak Lot 111429/02/04 02:24 102.457 Peak Level03/03/04 116 11:42 102.620 101.655

17:30 0.596 103.159 103.147 103.160 102.88018:32 102.887 Peak Level20:01 102.867

05/03/04 07:45 102.56

APPENDIX 1Water level observations from various sources, December 2003 TO March 2004

1. Observations from Recorder G8140407

This recorder is located east of Victoria Hwy. just before the turn off to low levelcrossing. This is a height recorder. This has recorded water levels from January todate.

1.1 Rainfall event of 16th and 17th February 2004:

Tindal Rainfall Recorder Height Recorder (G8140407)09:00 - 15/2 to 09:00 - 16/2 42mm 16/02/04 17:11 101.32709:00 - 16/2 to 09:00 - 17/2 92mm 16/02/04 18:00 101.547

16/02/04 23:35 101.72817/02/04 04:54 101.78517/02/04 06:41 101.80217/02/04 08:00 101.80217/02/04 10:48 101.77917/02/04 15:16 101.73817/02/04 22:30 101.647

1.2 Rainfall event of 23rd and 24th February 2004:

Tindal Rainfall Recorder Height Recorder (G8140407)09:00 - 22/2 to 09:00 - 23/2 128mm 22/02/04 08:01 101.66209:00 - 23/2 to 09:00 - 24/2 44mm 22/02/04 09:57 101.945

22/02/04 17:13 102.12622/02/04 20:45 102.30523/02/04 00:14 102.34923/02/04 01:12 102.35423/02/04 02:24 102.34223/02/04 17:47 102.26124/02/04 02:03 102.17824/02/04 09:00 102.077

1.3 Rainfall event of 28th February 2004:

Tindal Rainfall Recorder Height Recorder (G8140407)09:00 - 27/2 to 09:00 - 28/2 80mm 28/02/04 02:07 101.339

28/02/04 04:03 101.42728/02/04 05:05 101.64128/02/04 09:07 101.85128/02/04 12:01 102.16628/02/04 18:21 102.35528/02/04 23:07 102.43729/02/04 17:47 102.26129/02/04 02:03 102.17829/02/04 09:00 102.07701/03/04 04:51 101.989

01/03/04 22:28 101.574

1.4 Rainfall event of 3rd March 2004:

Tindal Rainfall Recorder Height Recorder (G8140407)09:00 - 02/3 to 09:00 - 03/3 80mm 03/03/04 02:40 101.663

03:25 101.76104:39 101.96107:17 102.26210:20 102.56213:40 102.76617:27 102.88018:32 102.88720:01 102.867

04/03/04 05:08 102.61613:11 102.37017:59 102.26223:15 102.176

05/03/04 08:43 101.93119:49 101.686

2. Manually Observed Flood Heights:

2.1 Lot 1114 Shed - Marks by Dave Bretherton

03.03.04 10:30 102.657 m AHD13:00 102.99914:00 103.06216:00 103.12917:30 103.159

2.2 Gauge Plate on Tree (near historic gauge station G8140408)

03.03.04 08:30 0.335 Gauge Board reading 102.290m AHD17:30 0.335 + 0.172 103.147m AHD

2.3 Historic Gauge Station ( G8140408)

03.03.04 08:30 0.862 Gauge Board Reading 102.267m AHD17:30 Arrow marking 103.160m AHD

3. First Culvert on Bicentennial Drive:

Invert level of the small culvert on Tindal Creek side = 101.470 m AHD(2 Nos of 37cm x 70cm)

Invert level of the big culvert on Tindal Creek side = 101.508 m AHD(2 Nos of 45cm x 102cm)

Middle of Bicentennial Drive above this culvert = 102.902 m AHD

4. Monitoring Bore levels:

The observed level of the monitoring bore at the Bicentennial Drive:

RN 2247505.03.04 - 07:45 102.56 m AHD (water table 0.23 m above ground level)18.03.04 - 17:30 101.905m AHD (water table 0.43 m below ground level)

The observed level of the monitoring bore at Uralla Road:

RN 22394

02.03.04 - 16:20 109.54m AHD (water table 1.27m below ground level)

Appendix 2 Flood extent and estimated water levelsThe extent of flooding in all the photographs was compared with the 1:5000 photo-image map of Katherine (1998) with 1m contours. A first pass estimate of the waterlevels was also noted.

Plate 1 Tindal Creek floodplain south west of Katherine East industrial area (waterlevel is above 103.0 m AHD). Drain 1 behind the industrial area is overflowing itsbanks. Photo 9599.jpg, 27/02/2004

Plate 2 Tindal Creek floodplain downstream of G8140407 (water level is above101.0m AHD.) Photo 9594.jpg, 27/02/2004

Plate 3 Tindal Creek floodplain and Drain 2 on the eastern side of Bicentennial Drive(water level is above 101.0m AHD). Photo 9596.jpg, 27/02/2004

Plate 4 Drain 2 near Walpiri Camp on the western side of Bicentennial Dve. confinedto its banks. Photo 9597.jpg, 27/02/2004

Plate 5 Tindal Creek at the Victoria Hwy. Flow is seen downstream of the newrailway bridge (water level just down stream of the bridge is above 100.0m AHD).Photo 9682.jpg, 27/02/2004

Plate 6 Drain 2 at Bicentennial Dve. (water level is above 101.0m AHD). Photo9685.jpg, 01/03/2004

Plate 7 Tindal Creek at Uralla Road (water level is above 105.0m AHD). Photo9689.jpg, 01/03/2004

Plate 8 Tindal Creek floodplain at Stuart Hwy. (water level is above 110.0m AHD).Photo 9690.jpg, 01/03/2004

Plate 9 Drain 1 behind the Katherine East industrial area (water level is above 103.0mAHD. Photo 9693.jpg, 01/03/2004

Plate 10 Drain 2 near Walpiri Camp on the western side of Bicentennial Dve. is fulland confined to its banks. Photo 9696.jpg, 01/03/2004

Plate 11 Drain 3 at Bicentennial Dve. (water level around Lot 1114 is above 101.0 mAHD). Photo 9697.jpg, 01/03/2004

Plate 12 Tindal Creek at Victoria Hwy. flowing just downstream of bridge (waterlevel is above 100.0m AHD.) Photo 9510.jpg, 01/03/2004

Plate 13 Tindal floodplain just south and south east of Lot 2980. The water level inthe vicinity of the height recorder is above 101.0m AHD. The water level from theheight recorder was about 101.65m around 17:00 hours. Therefore the water levelbelow the restriction in the Tindal drainage area is likely to be 101.6m AHD. Photo9537.jpg, 01/03/2004

Plate 14 Lot 1114 Bicentennial Dve. At 11:10 hours water was flowing from right toleft. (Water level is above 102.0m AHD.) Photo 9849.jpg, 03/03/2004

Plate 15 Victoria Hwy. at north side of railway overpass. At 11:15 hours that thewater level was lapping onto the highway (water level about 101.0m AHD.) Photo9850.jpg, 03/03/2004

Plate 16 Victoria Hwy. just north of the railway overpass. At 12:00 hours water wasjust over flowing the highway (water level is about 101.0m AHD.) Photo 9852.jpg,03/03/2004

Plate 17 Novis Quarry road. At 11:30 hours, a tributary of Tindal Creek wasoverflowing the road (water level at the crossing more than 99.0m AHD.) Photo9851.jpg, 03/03/2004

Tindal Creek was overflowing the old Victoria Hwy. at about 11:30 hours on03/03/04. The estimated water level at the crossing was above 100.0m AHD (nophotograph, observation made by R. Farrow).

Tindal Creek peaked around 10:30 hours on 03/03/04at the first crossing on StuartHwy. and was rapidly flowing about 0.5m over the road. The estimated water level atthe crossing was above 109.0m AHD (no photograph, observation made by R.Farrow).

Figure 1 Locality Map

!(

!(

!(

!(

!(

$

$

$

$

Drain 1

Drain 2

Drain 3

DR014903

G8140407

G8140408

RN022392

RN022394

RN022397

RN022475

RN029429

Tindal Creek

Vict

oria

Hw

y.

Ur a

lla R

d.

Stuart Hwy

Katherine

RAAFTindaBase

Collins Rd.Bicente

nnial

Dve.

Zimmin

Dve.

Cragborn

Rd.

Kath

erin

e

River

Lot 1114 214221432144

G8140001

DR014932

Figure 2 Daily rainfalls at Tindal AWS and Katherine, 1 December to 22 March (24Hr rainfall readings to 9am on the day listed)

0

50

100

150

200

250

300

1/12/2003

8/12/2003

15/12/2003

22/12/2003

29/12/2003

5/01/2004

12/01/2004

19/01/2004

26/01/2004

2/02/2004

9/02/2004

16/02/2004

23/02/2004

1/03/2004

8/03/2004

15/03/2004

22/03/2004

Rai

nfal

l (m

m)

Tindall AWS Katherine Railway Bridge

Figure 3 Longitudinal Section of Tindal Creek

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000Distance Downstream from Uralla Rd.(metres)

84

88

92

96

100

104

108

Elev

atio

n (m

etre

s A

HD

)

LONGITUDINAL SECTION OF TINDAL CREEK

Uralla Rd.

Katherine River

Drain 3

Industrial Area Drain 1Drain 2

Floodplain constriction Victoria Hwy.

Old Victoria Hwy.Tributary on left bank

Figure 4 Daily rainfalls and water levels from G8140407

0

20

40

60

80

100

120

140 0

20

40

60

80

100

120

140 1.0

1.4

1.8

2.2

2.6

3.0

0

20

40

60

80

100

120

140

G8140407 Water Level (metres)

I\~ ! ~ . I Rail Bridge

Daily Rainfall (mm)

- 1

1I 1I lJi I. I. _.t tt lliih: I I .IJId _.11 •. _1.11 .11 .0 I

nndalAWS

Daily Rainfall (mm)

•

JdiE I I :k m· :IIbtl I • 1.11.[ .1 --. i

Daily Rainfall (mm)

• • ~n · I • I .GW .1. 11 • __ .1. 1I • •• _11 •• 11 .1. , .- I

Janurary 2004 Feburary 2004 March 2004

Figure 5 Katherine flood depth and extent – pre railway

KATHERINE RIVER FLOOD DEPTH and EXTENT

at RAILWAY BRIDGE GAUGE HEIGHT 17.Sm

A •• ~ 0.0111 0.0 _ O.$m

A •• ~ o.olll O.$ - I .lm

A •• ~ 0.0111 I.l - l.Om

A •• ~ 0.0111 ,.l.Om

Ri,. • . er"" or ~ .. i.

Figure 6 Katherine flood depth and extent – post railway

KATHERINE TOWN AREA

KATHERINE RIVER FLOOD DEPTH and EXTENT

at the OLD RAILWAY BRIDGE HEI GHT

-,_ """"00- o~_ ...

,_ """" 0.' _" "",.. ._ """. , , . , 0 ..... ""

._ """" >'-0 ..... ' .. ,...,_."

" c' ... . , ..... "reo ... ,"""""'" "''''''''''

Figure 7 Bore water levels from selected observation bores between Katherine and TindalRAAF Base.

Figure 8 Bore water levels and Katherine annual rainfall.

RN029429 TINDALR.A.A.F

RN022392 TINDALRAAF

RN022394 URALLA Rd

RN022475 KATH GOLFCLUB

RN022397 DEPOT90

99

108

117

126

135

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

GroundwaterLevel

Metres AHD

NT Water Resources HYPLOT V125 Output 09/03/2004

Period 20 Year Plot Start 00:00_01/06/1985 1985-05Interval 1 Year Plot End 00:00_01/06/2005

RN029429 TINDAL R.A.A.F 115.00 Point Level (AHD)RN022001 VENN 2/81 100.11 Point Level (m) GSG8140001 KATH. RWY BRIDGE 10.00 Total Rainfall (mm)

115

119

123

127

131

135

115

119

123

127

131

135

500

750

1000

1250

1500

1750

85/8686/8787/8888/8989/9090/9191/9292/9393/9494/9595/9696/9797/9898/9999/0000/0101/0202/0303/0404/05

Figure 9 Daily rainfall at Tindal DR014932 and average daily water level in bore RN029429Note: 24hr rainfall readings to 9am on the day measured

Figure 10 Groundwater level contours (height above sea level) on 3/3/2004

Groundwater Flow

130.265

101.655

102.505

109.54

-0.22

-0.17

1.28

2.6

Limit of TindallLimestone

Limit of Tindall Limestone

130

120

11010

8

106104102

Ura

lla R

d

Stuart Hwy.

Bicenten

nial Dve

.

109.54

1.28

Observation bore

Water depth below ground level (M)Note: negative valuesare above ground level

Water level (Metres AHD)

0

100

200

300D

aily

Rai

nfal

l (m

m)

6/12

/03

20/1

2/03

3/1/

04

17/1

/04

31/1

/04

14/2

/04

28/2

/04

13/3

/04

Date

124

125

126

127

128

129

130

Wat

e r le

vel (

met

res

abo v

e se

a le

vel)

Ground levelat RN29429