**2. SPP strategy**

Normally, a natural or artificial lake may comprise multiple incoming and outgoing rivers that collect the rainwater/wastewater from upstream of the lake and drain the lake water to downstream, respectively. The SPP strategy is achievable if an internal levee with sluice gates is built in the lake. By doing so, flood disasters (too much water) of the watershed will be significantly reduced, water shortage problem (too little water) can be alleviated simultaneously, the siltation rate is reduced (too turbid) and clean water resources are protected against pollution. These two levees around the lake shoreline together would form an artificial canal or by-pass channel (BPC) as shown in Fig. 3. The inner bank of the

Novel SPP Water Management Strategy and Its Applications 245

*Protection against external pollution*: when the good quality floodwater enters the lake, this water is protected by the inner levee as the sluice gates are closed when the incoming river water quality becomes poor later. Thus the external contaminants in the rivers cannot mix with the clean water in the lake. In this stage (drought periods), the river water and the lake

*Prevention of water degradation*: As most of unwanted water (heavily polluted and high sediment-laden) will be concentrate in the BPC where the cross-section area is much smaller relative to the lake, thus for a certain discharge at the outlet, the velocity in the BPC will be rather fast. Consequently, the high level of turbulence will disperse all aggregated flocs and to purify the water, and the flow is capable to carry the sediment to the downstream without deposition. It may be hard to imagine that the water quality in the "by-pass canal" will be better than the water without the canal in the same conditions. This seems counterintuitive as most of unwanted water would flow in the canal surrounding the lake. But this is possible because, as mentioned early, hydrodynamic parameters are also a dominant factor for eutrophication and sedimentation, responsible for the appearance of algal blooms. It is often observed that higher velocities can prevent blooms/siltation from developing, and slow water movements create an almost quiescent environment where phytoplankton grow quickly with favourable nutrient, light and temperature conditions because microbial

*Too Much*: The above analysis shows that the proposed scheme can well solve the "unwanted water" ( i.e., too dirty and too turbid) problem. Furthermore, the flood disaster can also be mitigated. Under natural conditions, i.e., without BPC in Fig. 3, the highly contaminated river water with first flushes at the beginning of flood period occupies a lake's storage capacity. Consequently, the active storage is not sufficient to accommodate the following peak flow and flood disaster occurs. SPP approach can considerably reduce the dead storage of a lake as all unwanted water is discharged to the downstream via BPC and does not occupy the lake's capacity, thus it significantly increases the effective flood-control

The flood disaster can be mitigated, because the sluice gates are normally closed during dry period, so that the water level in the lake is very low due to regulation and water use after last year's flood period. Then just before the onset of the rainy season, water level in the lake is very low, and the low level can be kept until the arrival of peak flow, during which the sluice gates is open, thus the water level in BPC and the rivers can be lowered to acceptable

In other words, with BPC, the lake can be operated intentionally, and the lake's storage volume can be kept to accommodate the coming floods. The strategy of transforming a lake to a flood retention zone can greatly expand its capacity for flood control. During flood seasons, the sluice gates are opened when the water level in the rivers reaches the designed high level. Once opened, the velocity of flood wave propagation will be increased as very low water level in the lake increases the hydraulic gradient, then the scheme can greatly mitigate flood disasters. At the same time it transforms the floodwater to clean lake water

*Too Little*: This innovative strategy of water management can also alleviate the water stress in a lake, because under natural conditions, water from the lake keeps losing by

that is protected from pollutants by enclosing levee with the sluice gates.

water are separated and the clean water is fully protected.

particles can stick together to organic aggregates.

storage of the lake.

level for disaster mitigation.

canal would be built in the lake and could be constructed using dredged sediments to deepen the BPC.

Fig. 2. Simplified hydrograph of runoff and wastewater yielded in a catchment

Fig. 3. Simplified water system for a lake and the proposed infrastructure for water resources development and pollution prevention

*Separation in space and time*: The sluice gates would be used to regulate the unwanted water. If the river water is heavily polluted or sediment discharge is very high, the sluice gates will be closed so that all polluted water by-passes the lake and is discharged to the downstream of the catchment via the lake outlets. During flood periods, nutrient concentration is very low, except first flushes, the water quality from all inflow rivers will be relatively good. In such case, the sluice gates will be opened so that clean floodwater can enter the lake and be stored. Thus the water separation can be conducted based on the quality of river water in time (flood/drought) and space, i.e., good quality water enters to the lake for storage; but unwanted water runs to the downstream via BPC. Without the BPC, the lake receives all sediment particles from the rivers, with the BPC, the sedimentation rate is reduced to the particle volume carried by the stored water that is only a small fraction of all sediment yielded by the catchment.

canal would be built in the lake and could be constructed using dredged sediments to

Qs

Qa

Fig. 2. Simplified hydrograph of runoff and wastewater yielded in a catchment

Jan. Flood period Dec.

Fig. 3. Simplified water system for a lake and the proposed infrastructure for water

*Separation in space and time*: The sluice gates would be used to regulate the unwanted water. If the river water is heavily polluted or sediment discharge is very high, the sluice gates will be closed so that all polluted water by-passes the lake and is discharged to the downstream of the catchment via the lake outlets. During flood periods, nutrient concentration is very low, except first flushes, the water quality from all inflow rivers will be relatively good. In such case, the sluice gates will be opened so that clean floodwater can enter the lake and be stored. Thus the water separation can be conducted based on the quality of river water in time (flood/drought) and space, i.e., good quality water enters to the lake for storage; but unwanted water runs to the downstream via BPC. Without the BPC, the lake receives all sediment particles from the rivers, with the BPC, the sedimentation rate is reduced to the particle volume carried by the stored water that is only a small fraction of all sediment

**Incoming flow**

resources development and pollution prevention

yielded by the catchment.

Sluice gate

outside dike

Time

**Outgoing flow** 

Runoff Qr

BPC(by-pass pollution canal)

inner dike

deepen the BPC.

Q(m3/s)

Qw

*Protection against external pollution*: when the good quality floodwater enters the lake, this water is protected by the inner levee as the sluice gates are closed when the incoming river water quality becomes poor later. Thus the external contaminants in the rivers cannot mix with the clean water in the lake. In this stage (drought periods), the river water and the lake water are separated and the clean water is fully protected.

*Prevention of water degradation*: As most of unwanted water (heavily polluted and high sediment-laden) will be concentrate in the BPC where the cross-section area is much smaller relative to the lake, thus for a certain discharge at the outlet, the velocity in the BPC will be rather fast. Consequently, the high level of turbulence will disperse all aggregated flocs and to purify the water, and the flow is capable to carry the sediment to the downstream without deposition. It may be hard to imagine that the water quality in the "by-pass canal" will be better than the water without the canal in the same conditions. This seems counterintuitive as most of unwanted water would flow in the canal surrounding the lake. But this is possible because, as mentioned early, hydrodynamic parameters are also a dominant factor for eutrophication and sedimentation, responsible for the appearance of algal blooms. It is often observed that higher velocities can prevent blooms/siltation from developing, and slow water movements create an almost quiescent environment where phytoplankton grow quickly with favourable nutrient, light and temperature conditions because microbial particles can stick together to organic aggregates.

*Too Much*: The above analysis shows that the proposed scheme can well solve the "unwanted water" ( i.e., too dirty and too turbid) problem. Furthermore, the flood disaster can also be mitigated. Under natural conditions, i.e., without BPC in Fig. 3, the highly contaminated river water with first flushes at the beginning of flood period occupies a lake's storage capacity. Consequently, the active storage is not sufficient to accommodate the following peak flow and flood disaster occurs. SPP approach can considerably reduce the dead storage of a lake as all unwanted water is discharged to the downstream via BPC and does not occupy the lake's capacity, thus it significantly increases the effective flood-control storage of the lake.

The flood disaster can be mitigated, because the sluice gates are normally closed during dry period, so that the water level in the lake is very low due to regulation and water use after last year's flood period. Then just before the onset of the rainy season, water level in the lake is very low, and the low level can be kept until the arrival of peak flow, during which the sluice gates is open, thus the water level in BPC and the rivers can be lowered to acceptable level for disaster mitigation.

In other words, with BPC, the lake can be operated intentionally, and the lake's storage volume can be kept to accommodate the coming floods. The strategy of transforming a lake to a flood retention zone can greatly expand its capacity for flood control. During flood seasons, the sluice gates are opened when the water level in the rivers reaches the designed high level. Once opened, the velocity of flood wave propagation will be increased as very low water level in the lake increases the hydraulic gradient, then the scheme can greatly mitigate flood disasters. At the same time it transforms the floodwater to clean lake water that is protected from pollutants by enclosing levee with the sluice gates.

*Too Little*: This innovative strategy of water management can also alleviate the water stress in a lake, because under natural conditions, water from the lake keeps losing by

Novel SPP Water Management Strategy and Its Applications 247

Fig. 4. Dr. John Snow and the map he used in 1854 to identify the source of cholera; this

Water filtration 1850 to 1930's

 Snow, London 1850

Cl Disinfection 1920 to

Time Immemorial 1850 1950

Fig. 5. Death rate of human being in the history, indicating the application of SPP could

reconstructed to minimize the adverse effect of reservoir sedimentation.

In its planning stage, engineers and decision makers used the same practice as they did for other reservoirs, i.e., no special measures had been taken to separate incoming water based on its quality, and nothing had been done to protect the reservoir water and to prevent external high turbidity water. Consequently the reservoir storage capacity was decreasing at an astonishing rate in the reservoir, which caused the unacceptable negative impact of rapid development of backwater sediment deposition. In 4 years time, the accumulative sediment silted in the reservoir reached alarming level, i.e., 4.44 ×109 m3, in other words, the reservoir's storage capacity had almost totally lost. Under such circumstance, engineers were forced to reconsider the strategy of water management, and the dam had to be

discover leads to the first application of SPP strategy in water management

Death Rate per 100,000 per year

200

100

immediately reduce people's death rate

gravity via its outlets, and the water level quickly drops after flood period. If the proposed scheme is applied, the clean water will be protected, and sufficient high quality freshwater during flood period will be kept in the lake through the drought period until the next rainy season just like a reservoir. In other words, the water level is still high even after flood period. This water can be used by the human society to sustain their developments. Most importantly, during dry periods, all sluice gates are closed, the inner levee protects the lake water against external pollution, and it also prevents unnecessary loss of lake water.

The core idea of SPP is that the water should be separated based on its quality or turbidity; the unwanted water should be prevented mixing with the clean water, and good quality water must be stored and protected. In other words, the residence time of unwanted water in an ecosystem should be as short as possible; while the detention time of wanted water (or clean water) should be as long as possible.
