THE WATER Resources Authority has published an update on the flooding that occurred across Jamaica between May and October last year.
Main areas that were flooded were Newmarket, St. Elizabeth; Chigwell, Hanover; New River, St. Elizabeth; Evergreen, Manchester; Porus and Harmons in Manchester.
This update presents the results of the monitoring carried out by the Water Resources Authority up to December 17, 2002.
NEWMARKET
Flood levels at Newmarket crested on November 8, 2002 at an elevation of 349.4m above sea level and an average water depth of 20.6m in the main depression. This level is 4.24m below the 1979 flood water level. The total area flooded was 2.22 km(2).
The water is now declining at an average rate of 0.06m per day. The water has withdrawn from the Newmarket-Leamington road. The Newmarket-Darliston road is still flooded. Calculations indicate that it will take in excess of 6 months for a total withdrawal of water from Newmarket. This time frame will be reviewed and refined as more data become available.
CHIGWELL
The floodwaters at Chigwell have peaked and declined completely by November 30, 2002.
NEW RIVER
All floodwaters at New River have drained off via the Black River into the Lower Morass and out to sea. The deliberate breaking of the most southern dam across the Black River facilitated the drainage. The Authority is now modelling the runoff for different rainfall events to determine a management model that will be implemented to prevent further flooding. Completion of the model is scheduled for the middle of this month.
EVERGREEN
Flooding of a topographic depression at Evergreen near Balaclava has resulted from groundwater draining from aquifers at full storage. The groundwater table has risen from 40.5 metres to 1.4 metres below ground.
Since December 11 the water levels in the flooded depression have started declining.
The Authority has intensified its mapping and monitoring at Evergreen and more detailed information will become available later this month.
PORUS
Groundwater levels continued to decline along the Williamsfield- Porus trough. As the groundwater declines, the springs draining the aquifer and flooding the road surface have also declined. The mined out depressions located along the old Melrose Hill Road have all dried up and two of four depressions along the new Melrose Hill Bypass road have also dried up.
The water in storage in the remaining two depressions continues to maintain flow to the south of the main road and into Redberry and on to the Milk River. The decline in water levels and surface flows are within the time frame of 153 days originally determined by the Authority for a return to preSeptember conditions.
Surface flows out of Redberry peaked on November 15, 2002 at 5.72 cubic metres per second (M(3)/sec.) or 108.8 million imperial gallons per day (migd). On December 17, the out flow was 3.62 m(3)/sec. or 69 migd. The St. Toolis Springs and canal flow peaked on December 6, 2002 at 2.81 m(3)/sec. or 53.4 migd.
Total outflow from the Porus area into the Milk River on December 17, 2002 was 7.73 m(3)/sec. or 147 migd.
HARMONS
The groundwater drained from the Manchester Highlands continued to increase flooding at Harmons in South Manchester. The increase in groundwater levels at Reeveswood and Harmons since the May/June rainfall event are:
Reeveswood 39 metres (from 84 to 45 metres below ground level)
Harmons 54.7 metres (from 56.4 to 1.7 metres below ground level).
The total area flooded at Harmons is approximately 0.46 km(2). The flooding:
Closed several bauxite mining pits operated by Alpart Mining Venture (AMV)
Cut the Green Pond road and the main road to St. Jago in Clarendon making both impassable
Inundated several houses and shops.
An estimate of the volume of water within the flooded depressions at Harmons exceeds 1.8 cubic metres or 400 million imperial gallons.
The Water Resources Authority says until the water table begins to decline it will not be able to give an indication of the time frame for a total withdrawal of the water.
However, the decline in the water table at the nearby Redberry borehole would suggest that the wave of water should pass through Harmons in a short time and a decline in the water table would then begin.
WATER QUALITY
The water quality assessment of the Porus and Newmarket areas indicate the following:
No contamination from the bauxite/alumina operations at Kirkvine.
Phosphate levels were less than 0.3 mg/l, well within the ambient water quality standards.
Nitrate concentration, though within the World Health Organisation (WHO) guideline value of 45 mg/l, was higher than expected varying from 6.16 to 12.76 mg/l.
Bacteriological quality as indicated by the coliform bacteria analyses was very poor.
At Redberry faecal coliform exceeded 2,400 MPN/100 ml (recreational standard 200 MPN/100 ml). The high count indicates the presence of faecal mater from a source very close to Redberry. This could be the impact of the absorption pits in Porus (between Melrose and Redberry) being flooded out.
There should definitely be no swimming in or ingestion of the floodwaters in the depressions or at Redberry. It is anticipated that as that flows and hence dilution, decline, the bacteria concentration will increase.
NEWMARKET
The analyses of samples from Newmarket indicate
Phosphate concentrations within the ambient standard of 0.3 mg/l.
Nitrate concentration within the ambient range of 0.1 7.5 mg/l.
High faecal bacteria at Newmarket and even higher at springs draining the flooded area. Groundwater flowing from Newmarket and discharging as springs at Bluefields pick up the high faecal bacteria from housing developments located between Newmarket and Bluefields. Absorption pits and latrines are the primary mode of sewage disposal in these housing developments.
No swimming in, or ingestion of these waters should be allowed.
