OPERATION OF A WATER SUPPLY DAM AT MALAYSIAN WATER ACADEMY ON 22 ND MAY 2017

OPERATION OF A WATER SUPPLY DAM AT MALAYSIAN WATER ACADEMY ON 22 ND MAY 2017

OPERATION OF A WATER SUPPLY DAM CONTENT 1.0 Dam Classification By Function Single, Double And Multiple Function 2.0 Dam Operation Conversant with Information given in the Designer s Manual and Data to be Collected and Documented by Operator 3.0 Water Quality in Deep Reservoirs Discussion on Water Quality, Its Determination and Treatment

continue 4.0 Discussion on Relevant Terms Gross, Active, Dead and Total Critical Volume and Critical Depth 5.0 Variable Drawoff Tower Function and Objective 1

Operation Of A Water Supply Dam 1.0 Dam Classification by Function 1.1 Function a) Water Supply b) Irrigation c) Hydro Power d) Flood Control e) Recreation (not specifically) f) Environmental (improvement to Wet Land) 2

1.2 Single, Dual and Multiple In Malaysia dams are constructed for a single, dual or multiple functions. For example:- Function Name of Dam (a) Single Water Supply Irrigation Hydro Power Sg Selangor Dam Pedu Dam Cameron Highland Dam 3

(b) Dual (i) Water Supply and Flood Control (ii)irrigation and Water Supply (c) Triple Water Supply, Irrigation and Flood Control Klang Gate Dam Arning Dam Timar Tasoh Dam 4

For a Water Supply Dam the Operator has control over the Impounded Water Quality Choose to release from any selected Inlet of the Variable Drawoff Tower To scour when the dam is filled to Top Water Level or Overflows Dams of any other Functions, Water Quality of Impounded Water is not emphasized. Thus, treating water from a Water Supply Dam is normally much easier. 5

2.1 Introduction 2.0 Dam Operation To be successful and effective in operating a Water Supply Dam, understanding of the Regulation and Information given in the Designer s Operation Manual and constant reference to data regulary collected and documented by the operator. 6

2.2 Conversant With Information Given And Information Gathered And Documented In Advance 2.2.1 Time of Travel Release of Sg Tinggi Dam ( Sg Buloh Dam) to the Intake at Bestari Jaya. The estimated time given by the Designer is 16 to 17 hours. For Sg Selangor Dam which is located further upstream of Sg Tinggi Dam is estimated to be 20 to 22 hours. The travelling time varies with flow quantity available in Sg Selangor. These two dams cater for the raw water supply of three Water Treatment Plants constructed about 1 ½ meters apart along Sg Selangor with a total design capacity of 2600 MLD initially. 7

In respect of quantity of release, consideration must be given to possible abstraction along Sg Selangor by farmers and manufacturers. Knowledge of Time of Travel is important to the Operator as dam release has to be affected prior to requirement to sustain continuous abstraction at the Intake. 8

2.2.2 Data to be Acquired by Operator Both at Intake and at Dam 9

TABLE 1 - INTAKE (a) Water level and quantity of flow in river i) Under normal flow condition Recording at 12 or 24 hourly interval is suffice ii) During drought Recording of level at closer interval is necessary. 6 to 8 hours is likely the frequency Objective For base flow volume and recession constant estimation. For base flow volume and recession constant estimation. For river level monitoring, the installation of an automatic level recorder is ideal. 10

TABLE 1 INTAKE (cont..) (b) Rainfall At intake and at tributaries (c) Other users likely are the following:- - Compensation water - Irrigation - Manufacturing - Water treatment plants upstream Objective For estimation of flow volume In relation to forecast of dam releases. To consider quantity required by others in estimating quantity of dam release. 11

Regular ACQUISITION OF DATA & THEIR APPLICATION TABLE 2 - DAM a) Catchment Area Upstream of dam b) Rainfall - In catchment of dam (daily) c) Characteristic of Impounded water - Frequency, initially weekly - Thereafter bimonthly or monthly Objective For impounded reservoir volume estimation. For estimation of possible increase in volume of impounded water. For planning the treatment of water released at different levels of the impounded reservoir. Monitoring the water quality by conducting limnological survey. 12

Regular ACQUISITION OF DATA & THEIR APPLICATION TABLE 2 DAM (cont..) Objective d) Dam Level (daily) For trending the decrease or increase in dam level and volume. Documenting the acquired data will indicate a cut back or increase in quantity of dam release. e) Record the date and quantity of dam release at each instance. This information coupled with base flow in river will enable the likely water quantity of dam release in the future. 13

2.2.3 Understanding of Recession Constant 14

Recession Constant For Sg Selangor Value obtained from the equation Flow at any time Flow t days later q=q o x k t Reliable values of k can be derived when it is consistently dry across a river basin for many days Total River flow = Spill Over Weir + Abstraction + Dam release inclusive of compensation water Base River Flow = Total River Flow Dam Release Min. Base Flow = Compensation Flow + Abstraction K t = 0.95 of base flow The objective is to be aware of the flow quantity in the river the next day. Recession constant applicable to any river reach 15

2.2.4 Rule Curve for Sg Tinggi Dam 16

Total Reservoir Storage (MCM) RESERVOIR CONTROL CURVES 2020 MLD 1900MLD 1700MLD 1300MLD 110 100 90 80 70 60 50 40 30 20 Abstraction rates of 2020, 1900, 1700 and 1300 MLD were selected at intake for Sg Tinggi Dam 10 0 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 17

Gross Storage = 103 Mm³ Dead Storage = 8 Mm³ Active Storage = 95 Mm³ Total Storage = Active Storage + Dead Storage 18

Elevation - metre 2.2.5 SG. TINGGI RESERVOIR Elevation-Storage-Area Curve 0 1 2 3 4 5 6 7 8 9 10 11 12 70 60 50 Availability of surface area at different elevation. 40 30 20 10 0 20 40 60 80 100 120 140 160 180 200 220 240 Storage cubic metre 1 x 10 6 19

The Storage / Elevation Curve enables volume to be calculated at any water level. Top Water Level = 57.0 M Sill of First Inlet =49.0 M of Drawoff Tower Sill of Second Inlet= 41.0M Sill of Third Inlet = 32.0M There are three Inlets for the Sg. Tinggi Dam 20

2.2.6 Advanced Formulation of Tabulation Related to Dam Volume-Sg. Tinggi Dam (a) Available volume between Depth Interval from Top Water Level to Sill of Third Inlet (3 rd ) of Variable Drawoff Tower To Note: Volume between the Top Water Level (TWL) and the 1 st inlet is variable depending on TWL available in Dam. Whereas volume between the 1st and 2nd Inlet, between the 2nd and 3rd inlet etc. is constant. (b) Tabulation of Volume between selected Dam Levels (c) Available volume at 0.5M and 1.0M Depth Interval. To Note: Formulation under (a) to (c) only need to be prepared once. 21

a) Available Volume between depth from Top water Level To Sill of Third Inlet of Variable Draw-off Tower M 57.0 53.0 49.0 45.0 41.0 Volume in Mm 3 0 10 20 30 40 50 60 70 80 90 100 24.99 (26.31% of Total Volume (TV)) 12.50 (13.16% of TV) 13.78 (14.50% of TV) 8.73 (9.19% of TV) 95 36.5 35.00 (36.84% of TV) 32.0 22

continue Top Water Level (TWL) = 57.00m 1 st Inlet Level = 49.00m Mid Level between TWL and 1 st Inlet = 53.00m 2 nd Inlet Level = 41.00m Mid Level between 1 st and 2 nd Level = 45.00m 3 rd Inlet Level = 32.00m Mid level between 2 nd and 3 rd Inlet = 36.50m 23

b) Tabulation of Volume Between Selected Dam Levels Sg.Tinggi Dam Dam Level (M) Volume between Dam Level and Percentage to Total Volume Balance of Volume and Percentage to Total Volume Top Water Level(TWL) of 57M to Mid Level of 53M between TWL and Sill Level of 49M of 1 st.inlet 57M to 53M. 53M to 49M Volume(Mm³) Percentage(%) Volume(Mm³) Percentage(%) 24.99 12.50 26.31 13.16 70.01 57.51 73.69 60.54 37.49 This 37.49 Mm³ is 39.46% of Total Active Volume of 95.00 Mm³ 24

Tabulation of Volume Between Selected Dam Levels Sg.Tinggi Dam Dam Level (M) Volume between Dam Level and Percentage to Total Volume Balance of Volume and Percentage to Total Volume Sill Level of 1 st Inlet of 49M to Mid Level of 45M between 49M and Sill Level of 2 nd Inlet of 41M 49M to 45M 45M to 41M Volume(Mm³) Percentage(%) Volume(Mm³) Percentage(%) 13.78 8.73 14.50 9.19 43.73 35.00 46.03 36.84 22.51 This 22.51Mm³ is 23.69% of Total Active Volume of 95.00 Mm³ From TWL of 57M to Sill Level of 41M of 2 nd Inlet the available Active Volume is 60(37.49 + 22.51)Mm³.Available Active Volume is 35(95-60)Mm³ or (100-39.46-23.69)36.85% remaining for release by the 3 rd Inlet. 25

(c) Available Volume between 0.5M and 1.0M depth interval The available volume at 0.5M and 1.0M depth interval can be derived from the Storage / Elevation Curve from Top Water to Sill of 2 nd Inlet. However since the available volume between the Sill of the 2 nd and 3 rd Inlet is only 35.0Mm³ or 36.84% of the Total Volume, tabulation of volume at 0.5M or 1.0M can be ignored. The reason being it is good practice of dam volume management to retain at least 60% as Critical Volume. At very abnormal dry whether the suggested figure of 60% may have to be raised. 26

2.2.7 Formulation of Contingency Plan in Advance of Dam Release Contingency Plan To facilitate implementation of the Plan, tabulations are formulated in advance to identify the rate (quantity) of release and the sustaining period at any particular rate of release. These tabulations need to be prepared only once. 27

Contingency plan can be formulated in advance for any active volume in dam and dam level. Criteria involved in a plan formulation are as follows: Volume of dam release i. A range of volume Values based on past record related to river flow quantity and current weather condition. ii. Sustaining period selected related to weather condition and active volume available. In contingency plan formulation rainfall is not taken into consideration during the planned period. Any rainfall occurs during the planned period is considered a bonus. 28

Example of Formation of Contingency Plan Status of available volume. in dam as on 5/7/2002 for Sg. Tinggi Dam:- Dam Level = 53.32M Total Active Volume = 74,140 ML or 78.04% of Total Active Volume of 95,000 ML Planning Strategy:- Consider Critical level, Critical volume & sustaining period Critical level Dam Level (m) Critical Volume Active Volume At Specific Level (ML) Volume Between Specific (Level) Percentage To Total Active Volume 53.32 74,140 75.26 26.640 1 st critical level of 49.00M 49.00 47,500 48.22 2 nd critical level of 47.00M 8,750 47.00 38,750 39.34 29

Sustaining Period Available Volume (ML) 1 st Critical Level (53.32M to 49.00M) Rate of Dam Release (MLD) 800 700 600 500 400 300 Sustaining Period In Days 26,640 33 38 47 53 67 89 2 nd Critical Level (49.00M to 47.00M) 8,750 11 13 15 18 22 29 Total 44 51 59 71 89 118 30

3.0 WATER QUALITY IN DEEP RESERVOIRS 3.1 Introduction Seasonal density or thermal stratification varies for shallow (less than 6M) and deep (greater than 6M) lakes and reservoirs. In shallow reservoirs, water temperatures and oxygen concentrations will depend on the amount of wind induced mixing. As surface water temperatures rise in relation to bottom waters, stratified density layers will form in the water column. 31

An oxygen deficiency will result at the sediment water interface, creating anaerobic conditions that will solubilize nutrients and metals from bottom sediments. Deep water bodies experience thermal stratification and form three distinct layers of water below the surface. Top layer is called epilimnion. Bottom layer is called hypolimnion. The layer between is called metalimnion (thermocline). 32

WATER QUALITY IN DEEP RESERVOIRS ATTC Thermocline:Intermediate/boundary layer that has sharp change in both temperature and density Epilimnion: Upper layer of well-mixed warm water 30 oc Epliminion (warm, aerobic, well-mixed) Thermocline (sharp change in both temperature & water density) Hypolimnion (cool, anaerobic, poorly mixed) Lake Hypolimnion: Lower layer, poorly mixed cool water. Low DO and anaerobic. 28.5 oc Thermal Stratification 33

The water quality and temperature in these layers differ and are as follows: Epilimnion Water is high in ph, temperature and dissolved oxygen but low in turbidity, colour, iron and manganese. These metals are higher in proportion in the insoluble form. Metalimnion - A thin layer with sharp change in water temperature and density. Hypolimnion - Water is low in ph, temperature and dissolved oxygen but high in turbidity, colour, hydrogen sulphide, iron and manganse. The greater proportion of these metals are in the soluble form due to the anaerobic condition resulting from very low in dissolved oxygen content. 34

3.2 (A) CASE STUDY -Raw Water a)demonstration by color intensity-malut Dam ATTC Raw Water at Varying Depth 3537

Case Study-Treated Water Treated Water at Varying Depth 36

3.2 (B) Case Study (b) WATER QUALITY - Sungai Tinggi Dam Parameter Epilimnion Hypolimnion 1.0 Physical Changes a) ph b) Colour (HU) c) Turbidity (NTU) 6.5 to 7.2 Higher value due to algae action (photosynthesis) 35 to 150 3 to 28 Sedimentation 6.0 to 6.5 Lower value due to Stratification. 375 to 625 Decay of vegetation and leaching of organic matter from the soil. 6 to 66 Result of suspended matter. d) Temperature C 30 to 32 Subject to sunlight and wind action. 28 to 29 Shielded by the thermocline. 37

Parameter Epilimnion Hypolimnion 2.0 Chemical Changes a) Dissolved Oxygen mg/l b) Iron mg/l c) Manganese (mg/l) d) Ammonia as N (mg/l) 5 to 7 Exposed to atmosphere and wind action. 0.40 to 1.50 High dissolved oxygen content (aerobic condition resulting in precipitation). 0.03 to 0.07 High dissolved Oxygen content. 0.10 to 0.13 Nitrification can bring about a reduction in ammonical Nitrogen in the aerated surface waters. 2 to 5 Shielded from atmosphere and wind action. 7 to 20 Low dissolved oxygen Content (anaerobic condition, Metal remain in soluble state). 0.07 to 0.30 Low dissolved oxygen content. 0.54 to 1.73 Increase in the cold anaerobic stagnant zone. e) Alkalinity as CaCO 3 (mg/l) 4.4 to 6.9 Algae remove calcium carbonate and CO 2 by photosynthesis. The result is an increase in ph and decrease in calcium carbonate. 8.9 to 17.2 38

3.3 Improvement of Water Quality 39

TREATMENT ATTC (3.3.1) Aeration (Physical Means) The function of aeration To introduce oxygen to the water. To remove carbon dioxide (resulting in increase of ph). Removal of iron and manganese is ph dependent, more so with manganese. (3.3.1 a)natural Way 40

Oxidation Of Fe & Mn Sg. Terip Dam In Reservoir 41

Oxidation Of Fe & Mn At Scour - Malut Dam 42

Oxidation Of Fe & Mn At Dam Outlet - Sg. Semenyih Dam 43

ATTC TREATMENT (3.3.1 b)man-made Aeration at Source (a) Dam 44

View Of Air Diffuser Sg. Terip Dam 45

SIDE VIEW OF DIFFUSER Reinforced rubber nose 20MM X 5 MM 20mm DETAILED C1 Stopper Cap Perforated stainless Steel pipe Cross Connector PLAN VIEW OF DIFFUSER C1 Concrete Sinker Stainless Steel pipe (grade 304) Concrete Sinker 0.75M 0.5M Red strip replaced by cluster of holes 5mm diameter strategically located Concrete Sinker 6M Perforated stainless Steel pipe Renforced Rubber Hose Threaded Ends C2 6M Cross Connector Cross Connector Stainless Steel pipe Cross Connector Source from UTM DETAILED C2 Stainless Steel pipe (grade 304) 46

Dissolved Oxygen (mg/l) Variation of DO vs Depth After Aeration at Location 2 6.00 5.50 5.00 01-09-02 Aeration Hrs: 0.00 15-09-02 Aeration Hrs: 118.77 29-09-02 Aeration Hrs: 221.39 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 1/9/02 15/9/02 29/9/02 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 4.7 4.6 4.5 4.5 4.4 4.4 4.3 4.2 4.0 3.9 0.4 0.3 0.3 0.3 0.2 0.2 0.2 0.2 0.2 0.2 0.0 4.5 4.3 4.2 3.0 2.7 2.5 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.2 1.9 1.5 0.3 0.2 0.1 5.9 5.8 5.8 5.2 5.0 4.9 4.1 4.0 3.8 3.8 3.9 3.9 3.9 3.7 3.7 3.6 3.6 3.3 2.3 1.2 1.1 47

Dissolved Oxygen (mg/l) Variation of DO at Different Drawoff Level DO (01.09.02) DO (15.09.02) DO (29.9.02) 6.50 6.00 1 st Drawoff Level = 73.00m 2 nd Drawoff Level = 66.60m Drawoff Level 3 rd Drawoff Level = 60.20m 5.50 5.00 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 4 th Drawoff Level = 53.80m 48

Reservoir 1 to 4 DO monitoring Points 1,3 and 4 located upstream of Point 2 2 Aeration Point adjacent to Drawoff Tower The flow path of the air flume should be at right angle to the flow path of the inflow to the dam. 49

TREATMENT (3.4) Use of Chemicals (Chemical Means) Chemicals in use :- Chlorine Chlorine Dioxide Ozone Potassium Permanganate (KMnO 4 ) 50

USE OF CHEMICALS (CHEMICAL MEANS) (a) Use of Potassium Permanganate, a favoured chemical Advantages Analytical Analysis Besides effective in removal of iron and manganese, it also helps in the reduction of TOC (Total Organic Carbon). The optimum dosage and time of reaction has first to be determined. Adverse Effect of Over Dosage Manganese add colour to water. 51

(a) Use of Potassium Permanganate JAR TEST ON USE OF POTASSIUM PERMANGANATE (KMn0 4 ) To determine KMnO 4 Dosage and Reaction Time Table 1 : Raw Water Quality Analysis Date 06/10/03 ph 6.21 Turbidity (NTU) 97.1 Apparent Colour (Pt.Co) 521 Manganese total (mg/l) 0.224 Manganese soluble (mg/l) 0.128 Iron (mg/l) 0.132 Aluminium (mg/l) 0.038 TOC 3.90 52

Table 2 : Jar Test Data Alum and Lime Prior Determine Date of Test 24/09/03 Beaker No 1 2 3 4 5 6 Pre-lime (mg/l) 2 2 2 2 2 2 Potassium Permanganate (mg/l) 0.00 0.10 0.20 0.30 0.40 0.50 Liquid Alum Dosage (as mg/l product) 24 24 24 24 24 24 Flocculant AN910 (mg/l) 0.10 0.10 0.10 0.10 0.10 0.10 Floc Size d 3 d 3 d 3 d 3 d 3 d 3 Settled water quality SW ph 6.13 6.12 6.15 6.10 6.08 6.11 SW Turbidity (NTU) 3.76 3.82 3.58 3.55 3.68 3.65 SW Colour (Pt-Co) 24 24 21 21 22 22 SW Fe (mg/l) 0.12-0.11 0.12 0.13 - SW Al (mg/l) 0.098-0.073 0.061 0.054 - SW Mn (mg/l) 0.096 0.091 0.082 0.066 0.078 0.085 SW TOC (mg/l) 2.7-2.1 1.8 2.7-53

Table 3 : Jar Test Data To Determine KMnO 4 Reaction Time Date of Test 24/09/03 Beaker No 1 2 3 4 5 6 Pre-lime (mg/l) 2 2 2 2 2 2 Potassium Permanganate (mg/l) 0.30 0.30 0.30 0.30 0.30 0.30 Reaction time for KMnO 4 Dosing (mm) 11 9 7 5 3 1 Liquid Alum Dosage (as mg/l product) 24 24 24 24 24 24 Flocculant AN910 (mg/l) 0.10 0.10 0.10 0.10 0.10 0.10 Floc Size d 3 d 3 d 3 d 3 d 3 d 3 54

Table 4 : Jar Test Data Settled water quality Beaker No. 1 2 3 4 5 6 SW ph 6.10 6.09 6.11 6.08 6.05 6.07 SW Turbidity (NTU) 3.08 2.85 2.72 2.75 2.73 2.71 SW Colour (Pt-Co) 20 19 18 18 18 19 SW Fe (mg/l) - 0.11 0.11 0.12 - - SW Al (mg/l) - 0.056 0.055 0.057 - - SW Mn (mg/l) 0.016 0.016 0.017 0.020 0.032 0.046 SW TOC (mg/l) - 1.9 2.0 2.1 - - Filtered water quality FW Turbidity (NTU) 0.341 0.348 0.335 0.329 0.389 0.350 FW Colour (Pt-Co) 6 6 6 5 6 6 FW Fe (mg/l) - 0.01 0.01 0.01 - - FW Al (mg/l) - 0.08 0.08 0.07 - - FW Mn (mg/l) 0.009 0.010 0.012 0.014 0.023 0.028 FW TOC (mg/l) - 1.7 1.8 2.0 - - 55

Use of Potassium Permanganate - SSP 1 556

b) Use of chemicals (Coagulant) Appropriate Choice of Coagulant 57

Coagulant PAC Filter SSP1 58

Coagulant Alum Filter SSP1 59

3.5 MONITORING THE WATER QUALITY OF IMPOUNDED WATER (a) Introduction Limological Survey is conducted regularly to monitor the water quality of the water at varying depth in the impoundment. (b) Objective To monitor the raw water quality at varying depth in the impoundment or dam. For a dam, the survey is conducted at varying depth in the Epilimnion, the Thermocline and at the Hypolimnion initially. Knowing the water quality at varying depth will anable the selection of appropriate facilitate water quality for treatment. 60

(c) Parameters To Monitor At surface and at each variable inlet point for a dam provided with a variable drawoff tower. The parameters to monitor are: a) ph b) Colour c) Turbidity d) Iron (Soluble and Insoluble Form) e) Manganese (Soluble and Insoluble Form) f) Dissolved oxygen g) Alkalinity h) Hydrogen Sulphide i) Ammonia 61

(d) Sampling Procedure Manner of Sampling (i) Use of depth sampler for sample collection. (ii) For dissolved oxygen, use of Dissolved Oxygen Probe dip in water. Sampling Point The crucial points to monitor are the following:- (i) Top water level (ii) Inlets of Draw-off Tower 62

(e) Frequency of Sampling Dam with Variable Inlets in the Drawoff Tower Sampling just below the water surface and at each Variable Inlet. Suggest sampling weekly for a month. Thereafter by monthly for a month. Subsequently at least monthly. 63

Dam without variable Inlet Drawoff Tower Sampling just below Water Surface and at three meter or more depth interval. 64

4.0 Discussion on Relevant Term 4.1 Introduction In Dam operation, the following terms are often uttered :- (a) Gross Volume(Total volume) (b) Total Volume (c) Active Volume (d) Dead Volume (e) Critical Volume (f) Critical Level 65

4.2 Discussion 4.2.1 Gross Volume It is defined as the volume when the dam is filled to Top Water Level(TWL) also known as Spillway Level 4.2.2 Total Volume Total Volume=Active Volume + Dead Volume 66

4.2.3 Active Volume Theoritically it is defined as the volume between TWL or any Top Level (surface level) at the point in time to the sill of the lowest Inlet of the Variable Drawoff Tower (VDT) when the dam is in operation. This is the case when the dam is provided with a VDT. Without a VDT, that is dam designed for direct abstraction e.g. the Klang Gates Dam, the lowest reference point is the invert of the pipe. 67

continue However in practice, not the total available active volume can be abstracted. Abstraction will cease when the remaining active volume above the lowest Inlet due to lack of hydraulic head to meet the rate of dam release quantity. The limiting dam level is estimated to lie about a few meters above the lowest inlet level and varies from dam to dam. 68

4.2.4 Dead Volume It is defined as the volume below the sill of the lowest Inlet of the VDT or invert of pipe for direct abstraction from dam. 69

4.2.5 Critical Volume The Critical volume is defined as the available volume in dam when dam release has to be regulated or control (restricted) to tie over an impending dry period. Water rationing may have to be implemented during controlled dam release period. Every dam has its critical volume. Such critical volume in any dam is not time specific or volume specific. It is very closely related to weather conditions. It is suggested for good volume management practice to retain at least 60% of dam active volume. 70

4.2.6 Critical Level The level at which the critical volume occurs is defined as the Critical Level. 71

X Meter Active Volume X Meter X Meter LOWEST Dead Volume 72

5.0 Variable Drawoff Tower(VDT) 5.1 Introduction In recent years dams were constructed with Variable Drawoff Tower located in the reservoir. The number of Inlet varies from a minimum of three or more. Large capacity dam has more than three inlets. 73

5.2 Objective Variable Inlet provide the following possibilities :- (a) Enables the selection of the quality of water to be abstracted. (b) To release less oxygenated water from the bottom of the dam (Hypolimnion) by scouring. 74

DRAWOFF TOWER DECK LEVEL +60.5M RESERVOIR FULL SUPPLY LEVEL +57.0M Wet Well Trash Screen HIGH DRAWOFF INLET IL +49.0M INTERMEDIATE DRAWOFF INLET IL +41.0M DRAWOFF INLET IL Valve +32.0M Air Valve SG. TINGGI DAM DRAWOFF TOWER Regulating Valve 75

SG. TINGGI DAM DRAWOFF TOWER VALVE ARRANGEMENT Parallel Face Sluice Valve Regulating Valve Guard Valve Air Valve Plan View 76

5.3 Method of Control at Inlet In Malaysia the methods of control are as follows:- (a) Syphon (b) Roller Gate (c) Value 77

SYPHON CONTROL EMPANGAN SG. TERIP DAM DRAWOFF TOWER 106.50M Active Volume X Meter TWL 103.00M 100.75M 99.65M 95.70M 94.60M 92.50M 91.50M 87.70M 86.60M 84.60M 83.50M 79.70M 78.60M Syphon No. 1 Syphon No. 2 Syphon No. 3 Crown Level = 100.75M Spill Level = 99.65M Inlet Soffit Level = 95.70M Inlet Cill Level = 94.60M Crown Level = 92.50M Spill Level = 91.50M Inlet Soffit Level = 87.70M Inlet Cill Level = 86.60M Crown Level = 84.60M Spill Level = 83.50M Inlet Soffit Level = 79.70M Inlet Cill Level = 78.60M Dead Volume 78

Gate Control Active Volume X Meter LOWEST Dead Volume 79

Valve Control TWL Butterfly Value Control Active Volume BUTTERFLY VALVE CONTROL X Meter Dead Volume SG. KELALONG DAM BINTULU, SARAWAK 80

When the dam is in operation, only the selected valve will be fully opened and the others are totally shut. The butterfly value in this case is not intended for regulating flow. They should be totally open or shut. In whatever form of control, the required quantity of discharge is regulated by a flow meter or value downstream. The Larner Johnson Regulating Value or a Fixed Cone Value is used. 81

Thank You 82