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Flood Management Stategy

10 Second Summary

Predictable high tides from the South China Sea will severely damage the PGC golf course. Associated heavy rainfall would further compound the situation. The high cost of renewal following such a devastating event(s) may be significantly reduced and the risk of severe and widespread damage reduced with the implementation of a strategy to combat these destructive natural episodes.

Introduction

The history of the Panaga Golf Club (PGC) is marked with a number of damaging flooding events. Recent floods in 1999/2000, 1995 and 1985 caused serious disruption to the golf course and a repair cost that ran into many hundreds of thousands of dollars.

The next major flooding event with a combination of very high tides and excessive rainfall is predicted during a two month period in Q4 2004 to Q1 2005.

With the exclusion of the Ringer's Dyke and numerous ponds on the PGC, to date, no detailed planning, strategies or structures have been developed to counter or minimise any future flooding event at the Panaga Golf Club. The PGC is at risk from both sides of the golf course. The South China Sea threatens with very high tides, while the Panaga Camp contributes to rainwater runoff flowing through the golf course during periods of excessive precipitation.

This document is an attempt to highlight the threat of flooding (from heavy rainfall and / or from high tides) and to promote a strategy to counter these damaging flooding events. If we adopt a 'wait and see attitude', we can risk serious widespread flooding across the golf course. Judged by the cost of repair caused by the flood damage in 1999/2000, the cost of future serious flooding events could exceed B$1/2 million.

The Panaga Golf Club Flood Management Project was devised as a vehicle to formulate a defence strategy against flooding, or a least to minimise the impact and cost of a serious flooding event.

Data Acquisition

In order to evaluate and model flooding patterns across the golf course, the PGC commissioned a detailed topographical survey. The scope of work included surveying of all topographic features and acquiring elevations of the area inside the boundary of Jalan Utara, the Panaga Club, the beach frontage and the area around E1 (essentially the area of the golf course). All the elevations were taken at less than 100m intervals for flat terrain areas and at every change of the terrain profile.

The survey was conducted using GPS-RTK (Global Positioning System-Real Time Kinematic) which is very precise, determining three-dimensional point positions real time. The survey was referred to two known control base stations which were established on the ground prior to the survey commencing. All distances were recorded to the nearest 0.01m (where possible) and all spot levels taken on natural surfaces.

Flood Modelling

BSP TSM conducted the flood modelling using the detailed survey data gathered specially for the PGC (100m spacing) and tidal / rainfall data from the BSP metrological database. The modelling was superimposed on satellite photographs of the golf course.

Interpretation of the PGC Flood Modelling

Predicted Flood Area (blue) Simulated at 0.9m above MSL, Panaga Golf Course

Significant flooding occurs with a tide at 0.9m above MSL (Mean Sea Level).

Flood modelling confirms the premise that high tides will firstly penetrate the golf course through the Panaga Sungai mouth (centre right of simulation), and by the sungai in E1 (extreme left of simulation). These two areas are currently unprotected.

The dyke which runs between the beach and the golf course (at an angle across the simulation) provides protection at this level of tide.

In the Panaga Sungai Basin high tides would initially flood the area bordering the main Panaga Sungai basin (behind the main channel) and in the area bordering Jalan Utara and the 2nd Green. In the most part, it would appear that the flooding ‘extends’ the limits of these ponds, overflowing at various points on their perimeter. In addition, rising tidal waters penetrate along the connecting spoon drains, ditches and sungais to further extend the inundation (see below).

In the E1 area, flooding will be experienced initially behind the 13th green / 14th tee area and in the jungle behind the Half-way House.

Other centres of flooding can be identified on the 4th / 15th Holes and on the 6th Hole (left of centre of the simulation). The flood pattern at these locations are the result of water moving along drainage channels, spoon drains and larger sungais from both the Panaga Sungai Basin and the E1 area.

Predicted Flood Area (blue) Simulated at 1.4m above MSL, Panaga Golf Course

A high percentage of the northern half of the golf course is now under water, with only part of the 8th Hole and 10th Hole exposed.

The Panaga Sungai Basin is now largely covering an area from the Maintenance Road (which crosses the course just to the south of the middle of the course) to the Panaga Club.

The flooding across the 15th, 4th and 7th fairways has continued to extend and now are fully connected to the floodwater from the Panaga Sungai Basin along the border of the Jalan Utara.

In the E1 area, the floodwater has continued to extend and now covers an area 100% of its former size. However, the modelling indicates the floodwater at E1 has advanced less and covered less of the golf course than at the Panaga Sungai Basin.

In summary, the following significant points can be interpreted from the modelling of flooding patterns across the PGC.

• Tidal flooding will occur through the Panaga Sungai mouth and the sungai at E1.
• At E1, the model appears to indicate a flooding event to be less destructive (in terms of coverage), than at the Panaga Sungai Basin.
• At 1.4m above MSL, the flooding event will cover approximately 60-70% of the golf course.

Consultation

Consultation with Nicolas Leong regarding the BSP Panaga Area Flood Management Project, confirmed the use of polders (large water catchment areas) to drain flooded areas, and the use of pumps to move the water from these polders into the sea. He confirmed a similar strategy could be used for the PGC, making use of the existing lakes and sungai's both on and off the golf course. The strategy envisaged by the PGC is complimentary with the views of the BSP Seria Flood Management Project.

The meeting confirmed that at present, there is currently no funding for the Panaga Area Flood Management Project. Correspondingly, no data has been collected, no modelling completed and no planning finalised. Unfortunately, there is a significant risk of a major flooding event before BSP would be able to implement a Panaga Area Flood Management Project. Because of the greater impact from flooding on the golf course, it will be necessary for the PGC to initiate protection measures before that of BSP, while ensuring the PGC strategy is complimentary to that of the wider BSP strategy.

PGC Flood Management Strategy

It is clear that there must be a co-ordinated strategy between the PGC Flood Management Strategy and the wider issues of the BSP Panaga Area Flood Management Project. Indeed, the PGC Flood Management Project has to be seen in the context of this larger picture and therefore must have similar strategies and objectives.

Flooding on the golf course may be the result of two events, high tides or heavy rainfall. In the worst possible case, both these events may coincide.

By far the most damaging effects to the fabric of the golf course occur from high tides. The saline water lying on the golf course for even short periods will kill the grass. While the enhancement and development of new catchment areas (polders) will help drain saline water away in time, the fact that the grass has been exposed to saline water at all, will probably be enough for the grass to need replacement. Damage to the golf course by erosion, is not of great concern (since the tide will transgress across the golf course slowly), but the debris that comes with the advancing flood may cause damage (logs, debris etc).

Prolonged heavy rainfall produces different problems to that of tides on the golf course. Firstly, there is the rainfall that falls on the golf course itself, which needs to drain into the catchment areas. Secondly, there is the water that has fallen elsewhere and is moving through the golf course in the Panaga Sungai (from the Panaga Camp). Being fresh water, the damage to grass will be less damaging, especially if the water can be drained into the catchment quickly. However, tropical monsoonal rainfall tends to be heavy and for a short duration, just the right combination for flash floods. For the golf course this may lead to the erosion of the existing water courses and the undermining of protective sungai walls. This in turn may develop into increased localised flooding. Long term, the solution would be to limit the access of water to the PGC and divert excess rainwater away from the golf course.

The combination of high tides and heavy rainfall could have a disastrous effect on the golf course. On the one hand, the tide would be inundating the golf course from the seaward side, while on the other, rainwater from the Panaga Camp area would not be able to drain off into the sea.

The PGC envisage the development of two independent polders (water catchment areas), one in the golf course, and the other at E1.

The Panaga Sungai Basin area in the middle of the golf course, already offers the features of a polder. However, the capacity will need to be enhanced and the walls protected. The Panaga Sungai Basin will have to be protected at its mouth (where it enters the South China Sea) and where the water enters the PGC from the Panaga Camp (behind the 2nd Green). Control at the mouth of the Panaga Sungai will eliminate flow into the polder from the seaward direction, and allow excess rainwater out when required. In addition, control at the entry point into the PGC will control excessive rainwater from the Panaga Camp and divert this water toward the E1 polder.

The development of a polder (water catchment area) in the E1 area will drain the southern part of the golf course and act as a diversionary polder for excess rainwater from the Panaga Camp.

In order to divert excess rainwater away from the golf course, sluice control would be required at the entry point into the PGC from the Panaga Camp (behind the 2nd green). A connecting drain along the Jalan Utara would remove the excess floodwater to exit into the E1 polder (see Appendices - Diverted Water Flow).