swip manual part 1

MANUAL FOR AGROHYDROLOGY

AND

ENGINEERING DESIGN

FOR SMALL WATER IMPOUNDINGPROJECT (SWIP)

Department of Agriculture BUREAU OF SOILS AND WATER MANAGEMENT

Diliman, Quezon City March 1997

TABLE OF CONTENTS

DESCRIPTION PAGE NO.

1. ESTIMATION OF RUN-OFF and DERIVATION OF INFLOW HYDROGRAPH1

1.1 Establishment of Project Data 11.2 Estimation of Basin Lag Time and Time Concentration 11.3 Computation for Rainfall Depth 21.4 Rainfall Increments Determination 21.5 Rearrangement of Rainfall Pattern 31.6 Derivation of Synthetic Unit Hydrograph 81.7 Convolution of Equation for Flood Hydrograph 9

2. FIELD WATER BALANCE COMPUTATION 10

2.1 Establishment of Cropping Pattern and Cropping Calendar 102.2 Computation of 80% Dependable Rainfall 102.3 Crop Coefficient and Crop Rooting Depth 112.4 Percolation Loss 112.5 Soil Water Holding Capacity 142.6 Actual Evapotranspiration 142.7 Change in Storage 142.8 Initial Storage 142.9 Estimation of Water Storage at End of Decade 142.10 Irrigation Efficiency 15

3. ESTIMATION OF 10-DAY RESERVOIR INFLOW 16

3.1 Estimation of 10-Day Inflow for Region I, II, & IV 163.2 Estimation of 10-Day Inflow for Other Regions 16

4. ANNEXES

A. Philippine Water Resources Region 24B. Climate Map of the Philippines 25C. Monthly Distribution of Potential Evapotranspiration

of Selected Places in the Philippines 27D. Planting Calendar 28

LIST OF TABLES

TABLE NO. PAGE NO.

1 Regression Coefficients of the Rainfall Intensity-Duration Frequency Curve for Different Locations 4

2 Soil Groups for Estimation of Watershed Index W. 6

3 Antecedent Moisture Condition for Estimation of Water Index W. 6

4 Values of Watershed Index W. 6

5 Adjustment of Watershed Index W for Antecedent Moisture Condition7

6 Recommended Retention Rate for Hydrologic Soil Groups 8

7 T/Tp versus q/qp for Dimensionless Hydrograph 9

8 Percolation for Different Soil Types 12

9 S W H C of Different Soil Textural Class 15

10 Regional Run-off Coefficient and % Monthly Baseflow Distribution 17

LIST OF FIGURES

FIGURE NO. TITLE PAGE NO.

1 Rearrangement of Rainfall Increments 5

2 Water Management Scheme and Crop Depending Variables for Field Water Balance for Irrigated Wetland Rice. 12

3 Crop Depending Variables for Field Water balance of Irrigated Corn. 12

4 Crop Depending Variables for Field Water balance of Irrigated Mungo. 13

5 Crop Depending Variables for Field Water balance of Irrigated Tomato. 13

6 Crop Depending Variables for Field Water balance of Irrigated Peanut. 14

AGROHYDROLOGIC STUDIES AND ANALYSES

There are 3 general computations to be considered in the study. These are as follows:

1. Estimation of Run-off and Derivation of Inflow Hydrograph (25 yrs.)2. Field Water Balance Computation3. Reservoir Inflow Computation

1. ESTIMATION OF RUN-OFF AND DERIVATION OF INFLOW HYDROGRAPH

This would require the following data and inputs to be taken from the project site. These are topographic map soil and land capability mp or report, land use/vegetation map or report and rainfall intensities. The following arranged procedures would be helpful in deriving the inflow hydrograph.

1.1 Establishment of the Project Data

a. Drainage Area, A, in sq. km.b. Mainstream length from outlet to highest ridge, L.c. Mainstream from outlet to point nearest basin centroid, Lc.d. Total fall (elevation difference) from highest ridge to outlet, H, in meter.e. Watershed gradient,

f. Soil type of watershed (dominant) to determine the soil group the identified soil type in the watershed belong to.

g. Watershed cover/land use.

1.2. Estimation of Basin Lag Time, TL and time of Concentration TC using Method, and Snyder’s Method (revised), Time to peak, Tp and peak runoff, qp.

a. Compute for unadjusted TL

(TL in hours)

Where: L = mainstream length from outlet to highest ridge, in miles LC = mainstream length from outlet to the nearest basin centroid. Y = watershed gradient a = 0.38 Ct = coefficient with values (Linsley’s):

1.2 for mountatins drainage area 0.72 for foothill drainage area 0.35 for valley drainage area

b. Adjust estimate of TL Adjusted TL (for ∆D = 0.4 ≠ )

Adjusted TL = TL + ¼ (∆D - )

1c. Compute time of concentration, TC, in hours.

TC = TL / 0.70

d. Compute the time to peak, Tp usingTp = ½ ∆D + TL (adjusted)

Where: ∆D = time duration of one inch of excess rainfall (USDA SCS) suggested values of ∆D as 0.5 hr. (or 0.40 hr.) where Tc < 3; 1 hr. where 3<Tc<6:1/5 Tc where Tc>6.

e. Compute the Peak rate of Runoff, qp, in cms/mm excess rainfall:

qp =

Where:A = drainage area, sq. km.TL = time lag (adjusted), hr.qp = cms/mm

1.3 Compute for rainfall Depth P for different duration D, utilizing equation:P = iD wherei = rainfall intensity computed using Rainfall Intensity Duration, Frequency

Curve for different location in the Philippines (Table 1). Gen. Equation :

D = Duration

The tabulation of rainfall depth Pi versus Duration Di is thus:

Duration, Rainfall Intensity Rainfall Depth Seq. No. D, Hr I, min/hr. P, mm 1 D1 = ∆D 1 P1 2 D2 = 2D1 2 P2 4 D3 = 3D1 3 P3 n Dn = 2Dn n Pn

1.4 Obtain rainfall increments ∆Pi and rearranged them according to three maximization patterns:

1. Peak ∆P1 at middle time position, i = n/2

2. Peak ∆P1 at 1/3 time position, i = n/33. Peak ∆P1 at 2/3 time position, i= 2n/3 + 1

The sequences for peak at the different positions mentioned are shown in figure I. Considering that the highest qp is usually computed or obtained from the 2/3 time position pattern,

the hydrograph to be derived will utilize this pattern without anymore working the other 2 patterns for comparison, thus tabulation would only be as follows:

2 Rainfall Increments Rearranged Rainfall Increments APi, mm in 2/3 Position of peak pi

________________________________________________________________________Seq. No.1. ∆P1 = P1 ∆P142. ∆P2 = P2 - P1 ∆P133. ∆P3 = P3 – P2 ∆P124. ∆P4 = P4 – P3 ∆P105. ∆P5 = P5 – P4 ∆P96. ∆P6 = P6 – P5 ∆P77. ∆P7 = P7 – P6 ∆P68. ∆P8 = P8 – P7 ∆P59. ∆P9 = P9 – P8 ∆P310. ∆P10 = P10 – P9 ∆P211. ∆P11 = P11 – P10 ∆P112. ∆P12 = P12 – P11 ∆P413. ∆P13 = P13 – P12 ∆P814. ∆P14 = P14 – P13 ∆P1115. ∆P15 = P15 – P14 ∆P15

This rainfall-increment pattern is subjected to estimation of losses in the next step for the determination of rainfall excess amounts.

1.5 For the rearranged rainfall pattern considered,

-Apply the Soil Conservation Service (SCS) Method to obtain Initial Abstraction, Ia: Ia = 0.2s Where: Ia = initial abstraction, in inches s = 1000 – 10 W = maximum potential difference between rainfall and runoff, in inches W = watershed index, also called the runoff curve number N or CN = function of soil group, antecedent moisture condition (AMC), and land use

cover in the watershed

- Refer to Table 2 (Soil Group), Table 3 (Antecedent Moisture Conditions, Table 4 Value of W for different land uses/covers, assuming AMC II) and Table 5 (Adjustments of W for AMC I and AMC III).

- The computed initial abstraction Ia is subtracted from the rainfall over the necessary initial number of time increment until Ia is satisfied.

- After subtracting Ia, a uniform retention rate f is applied in succeeding time increments so that retention depth subtracted each time from a rainfall increments is at most equal to f AP, Applicable values are given in Table 6.

3

TABLE 1 Regression Coefficients if the Rainfall intensity, f (mm/hr) – Duration, t (hr) Frequency, T Curve for Different Locations: General Equation: i = aT C

(t+b)d

Note:

If b - Ø the resulting rainfall intensity-duration-frequency curves are straight lines (plotted on log, log chart).

4

REGION STATION/LOCATION a b c d R

1 Vigan, Ilocos Sur 47.295 0.20 0.2710 0.577 0.9882 Baguio City 51.414 - 0.2337 0.343 0.9800

Laoag City 60.676 0.30 0.2370 0.554 0.9944

2 Tuguegarao, Cagayan 47.263 0.40 0.2290 0.598 0.9949

Aparri, Cagayan 53.503 0.20 0.2780 0.610 0.9916 3 San Agustin, Arayat,

Pampanga 48.749 0.40 0.2330 0.690 0.9973 Sta. Cruz, Pampanga 41.687 0.85 0.2220 0.611 0.9976 Dagupan, Pangasinan 53.665 0.10 0.1340 0.575 0.9959 Matalava, Lingayen 0.890 0.10 0.2220 0.611 0.9973 Iba, Zamabales 51.960 0.80 0.2020 0.448 0.9951 Cabanatuan City 62.961 0.20 0.1395 0.754 0.9950 Cansinala, Apalit, Pampanga 36.597 - 0.2280 0.568 0.9962

Gabaldon, Nueva Ecija 43.209 0.10 0.2150 0.487 0.9942 4 Infanta, Quezon 67.327 0.30 0.2010 0.617 0.9867 Calapan, Mondoro Or. 54.846 0.30 0.2460 0.768 0.9969 MIA 46.863 0.10 0.1940 0.609 0.9979 Pot Area, Manila 58.798 0.20 0.1980 0.679 0.9981 Tayabas, Quezon 39.710 - 0.1320 0.461 0.9912 Casiguran, Quezon 77.587 0.70 0.2380 0.717 0.9849 Alabat, Quezon 55.424 0.20 0.2310 0.491 0.9880 Ambalong, Tanauan, Batangas 41.351 - 0.2310 0.511 0.9620 Angono, Rizal 62.314 0.70 0.1910 0.630 0.9934 5 Daet, Camarines Norte 44.553 - 0.2240 0.570 0.9971 Legaspi, City 55.836 0.20 0.2480 0.591 0.9958 Virac, Catanduanes 49.052 0.20 0.2480 0.591 0.9958 6 Iloilo City 44.390 0.15 0.2040 0.670 0.9970 7 Cebu Airport 59.330 0.40 0.2400 0.812 0.9956 Dumaguete City 100.821 1.00 0.2370 1.057 0.9963 8 Borongan, Eastern Samar 51.622 0.10 0.1680 0.581 0.9972 UEP, Catarman, Samar 61.889 0.40 0.2300 0.681 0.9905 Catbalogan, Samar 51.105 0.10 0.2020 0.620 0.9948 Tacloban, Leyte 39.661 0.10 0.1660 0.629 0.9968 9 Zamboanga City 48.571 0.30 0.2090 0.803 0.9973 10 Cagayan de Oro 78.621 0.50 0.1950 0.954 0.9992 Surigao City 61.486 0.60 0.2520 0.602 0.9901 Binatuan, Surigao del Sur 57.433 0.10 0.1340 0.577 0.9932

11 Davao City 81.959 0.50 0.1740 0.945 0.9986

TABLE 2: Soil Groups for Estimation of Watershed Index W

Soil Group Description of Soil Characteristics

A Soils having very low runoff potential, For Example, deep sands with little silt or clay. B Light soils under/or well structured soils having above Average infiltration when thoroughly melted. For example, light sandy loams, silty loams. C Medium soils and shallow soils having below-average Infiltration when thoroughly melted. For example, clay loams. D Soils having high runoff potential. For example, heavy soils, particularly days of high swelling capacity, and very shallow soils underlain by dense clay horizons.

TABLE 3: Antecedent Moisture Conditions for Estimation of Watershed Index W

Antecedent Moisture Condition Rain in pervious 5 days (AMC) Dormant Season Growing Season

I less than 0.5 in. lass than 1.4 in. II 0.5 – 1.1 in. 1.4 to 2.1 in. III more than 1.1 in. more than 2.1 in.

TABLE 4: Values of Watershed Index W (Assuming Antecedent Moisture Condition II)

Land Use or CoverFarming Hydrologic SOIL GROUP

Treatment Condition A B C D Native pasture - Poor 70 80 85 90 or grassland - Fair 50 70 80 85 Good 40 60 75 80Timbered Areas - Poor 45 65 75 85 Fair 35 60 75 80 Good 25 55 70 75Improved Permanent

Good 30 60 70 80 pastures Rotation pastures Straightrow Poor 65 75 85 90 Good 60 70 80 85 Contoured Poor 65 75 80 85 Good 55 70 80 85Crop Straightrow Poor 65 75 85 90 Good 70 80 85 90 Contoured Poor 70 80 85 90 Good 65 75 80 85Fallow - - 80 85 90 95

6(Table 4 Con’t)

The meaning of the terms listed under the heading “Hydrologic Condition” are as follow:

a. Native pastures: Pastures in poor condition is sparse, heavily grazed pastures with less than half the total watershed area under plant cover. Pasture in fair condition is moderately grazed and with between half and three-quarters of the catchment under plant cover. Pasture in good condition is lightly grazed and with more than three-quarters of the catchment area under plant cover.

b. Timbered areas: Poor areas are sparsely timbered and heavily grazed with no undergrowth. Fair areas are moderately grazed, with some undergrowth. Good areas are densely timbered and ungrazed, with considerable undergrowth.

c. Improved permanent pastures: Densely sown permanent legume pastures subject to careful grazing management are considered to be in good hydrologic condition.

d. Rotation pastures: Dense, moderately grazed pastures used as part of a well planned, crop-pasture-fallow rotation are considered to be in good hydrologic condition. Sparse, overgrazed or “opportunity” pastures are considered to be poor condition.

e. Crops: Good hydrologic condition refers to crops which form a part of a well planned and managed crop-pasture-follow rotation. Poor hydrologic condition refers to crops managed according to a simple crop-follow-rotation.

TABLE 5: Adjustment of Watershed index W for Antecedent moisture Condition

Corresponding Value of W for:AMC = II AMC = I AMC = III

100 100 10095 87 9990 80 9885 70 9780 65 9575 60 9070 50 9065 45 8560 40 8055 35 7550 30 7045 25 6540 20 6035 20 5530 15 5025 10 45

7

TABLE 6: Recommended Retention Rate for Hydrologic Soil Group (USBR)

Hydrologic Soil Group Retention Rate, inches/hour

A 0.4B 0.24C 0.12D 0.04

1.6 Derive the synthetic unit hydrograph, using T/Tp versus q/qp for dimensionless hydrograph (Table 7)

-interpolate from the values of Table 7 the selected values of discharge ratios q/qp for values of time ratio equal to

T/Tp = ∆D , 2∆D , 3∆D etc. TP TP TP Until q/qp is less than 0.001

-Compute the ordinate of Synthetic Unit hydrograph as follows: Ui = (q/qp) i qp Where: Ui = ordinate of synthetic unit hydrograph in cms/mm (i= 1, 2, 3 . . . ) q/qp I = interpolated value of q/qp from smooth dimensionless hydrograph. qp = Computed peak rate of runoff in cms/mm

-Obtain correction factor k for synthetic unit hydrograph K = 3.6 Σ U 1 ∆D A

-Correct to ordinate Ui ( i = 1, 2, 3 . . . ) Uu (Corrected Ui) = original Ui K

-To check, K should be equal to one when using the same formula: K = 3.6 Σ U 1 ∆D A

-In tabulated form we will have:

Seq. No. Time Dimensionless Hydrograph Unit Hydrograph Cms/mmi T, hr T/Tp q/qp Ui = (q/qp) i qp Uu = Ui/ki

1 ∆D ∆D/Tp Values (q/qp)1 qp Uu1

2 2∆D 2∆DTp interpolated (q/qp)2 qp Uu2

3 3∆D 3∆D/Tp From (q/qp)3 qp

4 4∆D 4∆D/Tp Table 7 (q/qp)4 qp

n n∆D n∆D/Tp (q/qp)n qp Uu n Σ Ui Σ Uu

8

(Dimensionless and ideally close to 1: D in hours; A in sq. km.)

TABLE 7: T/Tp versus q/qp for dimensionless hydrograph

Time Ratio Disch. Ratio Time Ratio Disch. RatioT/Tp q/qp T/Tp q/qp

0 0 1.5 0.66

0.1 0.015 1.6 0.56

0.2 0.175 1.8 0.42

0.3 0.16 2 0.32

0.4 0.28 2.2 0.240.5 0.43 2.4 0.180.6 0.6 2.6 0.130.7 0.77 2.8 0.0980.8 0.89 3 0.0750.9 0.97 3.5 0.0361 1 4 0.018

1.1 0.98 4.5 0.0091.2 0.92 5 0.0041.3 0.84 Infinity 01.4 0.75

1.7 To the rearrange pattern of excess rainfall, apply the synthetic unit hydrograph Qi ( i = 1, 2, 3 . . . ) according to the convolution equations:

Q1 = U1 E1

Q2 = U1 E2 + U2 E1

Q3 = U1 E3 + U2 E2 + U3 E1

Q4 = U1 E4 + U2 E3 + U3 E2 + U4 E1

etc.

\

9

2. FIELD WATER BALANCE COMPUTATION

Establish the best cropping pattern and cropping calendar with the following objectives: a) minimum irrigation requirements; b) maximum annual production; c) optimum growing conditions for the given crop and growing stages: d) grow paddy rice during wet season when water

abundant and irrigation is minimal.

Fill the column for the rainfall (rain) with 80% dependability computed using the two parameter log-normal distribution and the average potential evapotranspiration (PET). To compute for 80% dependable for a given site the following procedures are to be considered:

a. Collect 10-day rainfall data, defined as the sums of daily rainfall over each defined 10-day period and arrange them as follows:

Y e a r

Month Decade 1 2 3 . . . N MeanStd. Dev.

Jan. 1 - - - . . . - - - 2 - - - . . . - - - 3 - - - . . . - - -

Feb. 4 - - - . . . - - - 5 - - - . . . - - - 6 - - - . . . - - -

Dec. 34 - - - . . . - - - 35 - - - . . . - - - 36 - - - . . . - - -

b. Compute the mean of 10 – day rainfall for all decades

K = 1, 2, 3 . . . . . . . . . . . . . . . 36 N XK = 1 Σ XKi N i =1 Where XK = mean of 10 – day rainfall in decade K XKi = 10 – day rainfall data in decade K and year 1

N = number of recorded observation in decade K in years.

c. Compute the standard deviation of 10 – day rainfall for decades K = 1, 2, 3 . . . . . . . . . . . . . . . 36

__ SK = 1 Σ (XKi - X )2

N-1 i=1

Where SK = standard deviation of 10 – day rainfall in decade K

d. Compute the coefficient of variation of 10 – day rainfall for all decades K = 1, 2, 3, ….36

10

e. Compute the standard normal deviation corresponding to an axceedance probability, p of 80 %, tp, for p = 80% tp = -0.831

Where ZK = coefficient variation

f. Compute the frequency factor for all decades K 1, 2, 3. . . . 36

Where: B = Ln ( 1 + Z2 ) KK = frequency factor in decade K

g. Compute the 10 – day rainfall at 80% dependability for all decades _ RK = XK + SK KK

Where: RK = 10 – day rainfall at 80% dependability

h. Tabulate the results as follows:

Month Decade XK SK ZK KK RK

Jan. 1 - - - - -

2 - - - - - 3 - - - - - . . . . . . . . . . . . . . . . . .

Dec. 34 - - - - - 35 - - - - - 36 - - - - -

Mean 80% dep or 10 – day rainfall at project site =

Fill- up the crop-coefficients (kc) and crop-rooting depth columns according to the establishment of cropping calendar and crop growing stages. Refer to Figures 2 to 6. For wetland rice, the crop coefficient at all stages can be assumed equal to one (1).

Make a reasonable assumption for probable percolation losses (mm/day) or refer to Table 8.

11TABLE 8: Percolation For Different Soil Types

Clay --------------------------------------------------------------------------------- 1.25 mm / day

Silty Clay --------------------------------------------------------------------------- 1.50 mm / day Clay Loam-------------------------------------------------------------------------- 1.75 mm / day Silty Clay Loam-------------------------------------------------------------------- 1.75 mm / day Sandy Clay Loam------------------------------------------------------------------ 2.0 mm / day Sandy Loam------------------------------------------------------------------------ 4.0 mm / day

Figure 2: Water Management Scheme & Crop Depending Variables Used In Field Balance Computation For Irrigated Wetland Rice

Rainfall Land Land Crop in the FieldCollecting Period Soaking Preparation (100 Days)

1 2 3 4 5 6 7 8 9 10 11 12 13

1 2 3 4 5 6 7 8 9 10 11 12 13

Maximum water200 80 80 80 80 80 80 80 80 80 80 10 0depth in paddy,

mmMinimum water

10 20 20 20 20 20 20 20 20 20 20 0 0depth, mm

Optimum water 100 65 65 50 50 50 50 50 45 45 45 0 0

depth, mm

FIGURE 3 Crop Depending Variables For Field Water Balance For Irrigated Corn

Rainfall Collection

Crop in the Field

& (110 Days)

Land Preparation

LP 1 2 3 4 5 6 7 8 9 10 11

LP 1 2 3 4 5 6 7 8 9 10 11Crop Coefficient 0.65 0.65 0.75 0.8 0.85 0.9 0.9 0.9 0.9 0.75 0.5Rooting Depth

(mm) 100 200 300 450 600 700 775 825 875 900 900

12FIGURE 4 Crop Depending Variables Used in the Field Water Balance For Irrigated Mungo

Rainfall Collection

& Crop in the FieldLand Preparation (80 Days)

LP 1 2 3 4 5 6 7 8

LP 1 2 3 4 5 6 7 8Crop Coefficient 0.35 0.5 0.7 0.9 0.9 0.85 0.77 0.7Rooting Depth 80 150 230 300 300 300 300 300

FIGURE 5 Crop Depending Variables Used in the Field Water Balance for Irrigated Tomato

Rainfall Collection & Crop in the Field

Land Preparation (80 Days)LP 1 2 3 4 5 6 7 8

LP 1 2 3 4 5 6 7 8Crop Coefficient 0.35 0.5 0.7 0.9 0.9 0.85 0.77 0.7Rooting Depth (mm) 80 100 300 400 500 600 700 700

13FIGURE 6 Crop Depending Variables for the Field Water Balance for Irrigated Peanut

Rainfall Collection & Crop in the Field

Land Preparation (100 Days) LP 1 2 3 4 5 6 7 8 9 10

LP 1 2 3 4 5 6 7 8 9 10

Crop Coefficient 0.40

0.70

0.70

0.95

0.95

0.95

0.75

0.75

0.75

0.55

Rooting Depth (mm) 80 150 200 250 300 350 400 500 600 600

2.5 Make a reasonable assumption of soil water capacities WHC in volume percentage of soils used for upland crops. (10% - 20%).Refer to Table 9.

2.6 Actual evapotranspiration (AET) is equal toAET = PET x KC

2.7 Change in storage (ΔSTOR) is equal toSTOR = RAIN - AET - PERCO - for paddy riceSTOR = RAIN - AET for upland crops.

2.8 Initial Storage (INIT) is estimated using the following formulaINIT = (Raini + Raini – 1) (0.70) for paddy riceINIT = (Raini + Raini – 1) (0.50) for upland crops

2.9 Estimate the water storage (STOR) at the end of a given decade:STORi = STORi – 1 + ΔSTOR

If STORi > allowable max storageThen DRAINAGE = STORi – allowable max storage

STORi = allowable max storage IRRIGATION = Ø. Ø

If STORi < allowable minimum storage Then IRRIGATION = Optimum Storage – STORi

STORi = Optimum Storage Drainage = Ø. Ø

ELSE IRRIGATION = Ø. Ø

DRAINAGE = Ø. Ø

14

Note: For upland crops, allowable min. soil moisture storage is usually assumed to 50% of soil water holding capacities in the root zone, that is 0.54 (WHC) (ROODEP). Do not irrigate during the last two decade of a given period.

2.10 Use an irrigation efficiency if 51% for paddy rice (lowland) and 54% for upland crops to the estimated net crop irrigation to get an estimate of system irrigation requirements.

TABLE 9 Soil Water Holding Capacities of Different Soil Textural Classes:

Soil Texture Total Available Moisture

Pv =Pw As Volume%

Sandy 8(6-10)

Sandy Loam 12(9-15)

Loam 17(14-20)

Clay Loam 19(16-22)

Silty Clay 21(18-23)

Clay 23 (20-25)

153. ESTIMATION OF 10 – DAY RESERVOIR INFLOW

3.1 For Regions I, III, IV, characterized by distinct wet and dry seasons, 10 – day reservoir inflow are estimated as follows:a. DQj = RCj . Pj

Where: DQj = direct runoff in decade j (mm)

RCj = runoff coefficient in decade j, equal to estimated mean monthly runoff coefficient Pj = 80% dependable rainfall

b. 10 – day Baseflow BFj = F .Qj – 1

Where: BFj = baseflow in decade j (mm)

F = 10 – day reservoir factor = 0.002 + 0.026 (D.A.) where DA is drainage area in sq. km. (This

regression equation analysis of several small watersheds <100 km2 In the country).

Qj – 1 = Total runoff (or inflow) in the previous decade (j-j), mm

c. 10 – day Reservoir Inflow Qj = DQj + BFj

Where: Qj = reservoir inflow in decade j (mm)

DQj = direct runoff in decade j (mm) BFj = baseflow in decade j (mm)

3.2 For the other regions in the country which are predominantly characterized by indistinct, short, or no dry season with more or less continuous rainfall, 10 – day reservoir inflow are estimated as follows:a. 10 – day Direct Runoff

DQj = RCj . Pj Where:

DQj = direct runoff in decade j (mm) RCj = runoff coefficient in decade j, equal to estimated monthly runoff

coefficients Pj = mean 10 – day rainfall in decade j (mm)

b. Annual Baseflow

BF = a + b . DA Where:

BF = annual baseflow a.b. = regression factor for the region where the project is located

(Table 10) D.A . = Drainage Area, (sq. km.)

c. 10 – day Baseflow Qj = DQj + BFj

Where: Qj = reservoir inflow in decade j (mm) DQj = direct runoff in decade j (mm) BFj = baseflow in decade j (mm)

16TABLE 10 Regional Run – off Coefficient and % Monthly Baseflow Distribution:

Region 1

Month Run - off Coefficient, RC

Jan. 0.25Feb. 0.05Mar. 0.03Apr. 0.03May 0.17June 0.37July 0.64Aug. 0.67Sept. 0.75Oct. 0.75Nov. 0.61

Dec. 0.25

Region 2

Month %Baseflow Run - off Coefficient, RC

Jan. 8.76 0.17Feb. 7.91 0.17Mar. 7.22 0.08Apr. 7.05 0.08May 6.7 0June 6.42 0.17July 7.39 0.2Aug. 8.18 0.34Sept. 9.37 0.4Oct. 10.43 0.41Nov. 10.84 0.44

Dec. 9.72 0.37

Linear Curve Fit : BF = a + b (D.A)

a = 286.021 b = -9.72 x 10-1 R = 0.74

17Region 3

Month Run - off Coefficient, RCJan. 0.45

Feb. 0.08Mar. 0Apr. 0May 0.24June 0.34July 0.58Aug. 0.7Sept. 0.75Oct. 0.7Nov. 0.4

Dec. 0.5

Region 4

Month Run - off Coefficient, RCJan. 0.45Feb. 0.44Mar. 0.19Apr. 0May 0June 0.19July 0.19Aug. 0.26Sept. 0.33Oct. 0.47Nov. 0.57

Dec. 0.5

Region 5

Month %Baseflow Run - off Coefficient, RCJan. 9.17 0.5Feb. 8.69 0.38Mar. 8.28 0.3Apr. 7.91 0.25May 7.64 0.1June 7.66 0.08July 7.86 0.15Aug. 8.08 0.15Sept. 8.31 0.15Oct. 8.53 0.35Nov. 8.79 0.39

Dec. 9.07 0.47

Linear Curve Fit : BF = a + b (D.A) a = 2, 057.31 b = 18.28 R = 0.87

18Region 6


Jan. 8.06 0.39Feb. 8.1 0.19Mar. 7.96 0.16Apr. 8.1 0.16May 8.26 0.16June 8.45 0.18July 8.66 0.44Aug. 8.73 0.44Sept. 8.6 0.33Oct. 8.47 0.49Nov. 8.37 0.39

Dec. 8.21 0.39


Region 7


Jan. 8.23 0.26Feb. 8.07 0.15Mar. 8.09 0.1Apr. 8.22 0May 8.23 0.09June 8.35 0.15July 8.47 0.3Aug. 8.66 0.3Sept. 8.57 0.3Oct. 8.45 0.3Nov. 8.37 0.3

Dec. 8.29 0.26


19Region 8


Jan. 9.1 0.38Feb. 8.8 0.28Mar. 8.6 0.25Apr. 8.3 0May 8.1 0.14June 7.9 0.22July 7.7 0.3Aug. 7.6 0.34Sept. 7.7 0.34Oct. 7.9 0.51Nov. 8.4 0.7

Dec. 9 0.7

Linear Curve Fit : BF = a + b (D.A) a = 12.52 b = 14.051 R = 0.872

Region 9


Jan. 8.53 0.3Feb. 8.33 0.22Mar. 8.16 0.08Apr. 7.94 0May 8 0June 8.13 0.07July 8.19 0.14Aug. 8.32 0.14Sept. 8.42 0.14Oct. 8.53 0.24Nov. 8.66 0.24

Dec. 8.76 0.3


20Region 10


Jan. 8.51 0.49Feb. 8.43 0.4Mar. 8.36 0.37Apr. 8.29 0.32May 8.21 0.15June 8.16 0.15July 8.21 0.15Aug. 8.27 0.24Sept. 8.3 0.24Oct. 8.34 0.28Nov. 8.4 0.25

Dec. 8.49 0.52


Region 11


Jan. 8.42 0.17Feb. 8.38 0Mar. 8.35 0Apr. 8.31 0May 8.3 0.12June 8.25 0.12July 8.27 0.29Aug. 8.3 0.29Sept. 8.32 0.26Oct. 8.34 0.26Nov. 8.37 0.23

Dec. 8.39 0.22

Linear Curve Fit : BF = a + b (D.A) a = 152.608 b = 7.53 R = 0.751

21Region 12


Jan. 8.13 0.21Feb. 7.99 0.12Mar. 8.03 0Apr. 8.13 0.13May 8.24 0.25June 8.39 0.35July 8.54 0.44Aug. 8.69 0.45Sept. 8.66 0.45Oct. 8.53 0.45Nov. 8.4 0.21

Dec. 8.26 0.21

Linear Curve Fit : BF = a + b (D.A) a = 1, 751.61 b = -4.018 R = 0.915

22

ANNEX A – I PHILIPPINE WATER RESOURCE REGIONS

Water Resources Region No. 1 – ILOCOSIlocos Norte, Ilocos Sur, Abra, Benguet, La Union and part of Mt. Province.Predominant Climate : Type I

Water Resources Region No. 2 – CAGAYAN VALLEYCagayan, Isabela, Nueva Viscaya, Quirino and parts of Mt. Province, Kalinga-Apayao, Ifugao and Quezon.Predominant Climate : Type III

Water Resources Region No. 3 – CETRAL LUZONNueva Ecija, Pamapanga, Pangasinan, Tarlac, Bulacan, ZamabaleS, Bataan and portions of Benguet and Aurora

Province.Predominant Climate : Type I

Water Resources Region No. 4 – SOUTHERN TAGALOGRizal, Cavite, Laguna, Batangas, Quezon and Metropolitan Manila in Luzon, and the island provinces of Marinduque, Mindoro, Romblon, and Palawan.Predominant Climate : Type I

Water Resources Region No. 5 – BICOLCamarines Norte, Camarines Sur, Albay, Sorsogon in the South-eastern Peninsula of Luzon and the inslands

of Catanduanes and Masbate.Predominant Climate : Type II and Type III and Type IV

Water Resources Region No. 6 – WESTERN VISAYASNegros Occidental, the sub-province of Guimaras, and the island of Panay which consist of the provinces of Aklan,

Antique, Capiz and Iloilo.Predominant Climate : Type I and Type III

Water Resources Region No. 7 – CENTRAL VISAYASCebu, Bohol, Siquijor, Negros OrientalPredominant Cliamate : Type III

Water Resources Region No. 8 – EASTERN VISAYASSamar and Leyte Islands.Predominant Climate : Type IV

Water Resources Region No. 9 – SOUTHWESTERN MINDANAOMisamis Occidental, Zamboanga del Sur and Zamboanga del Norte together with Sulu Archipelago.Predominant Climate : Type III and Type IV

Water Resources Region No. 10 – NORTHERN MINDANAOAgusan del Norte, Misamis Oriental and part of Agusan del Sur, Bukidnon and Lanao del Norte.Predominant Climate : Type II

Water Resources Region No. 11 – SOUTHEASTERN MINDANAODavao del Sur, Davao Oriental and Surigao del Sur and South Cotabato provinces.Predominant Climate : Type II and Type IV

Water Resources Region No. 12 – SOUTHERN MINDANAOLanao del Norte, Lanao del Sur, Bikidnon, North Cotabato, Maguindanao, Sultan Kudarat and South Cotabato.Predominant Climate : Type III and Type IV

24

PLANTING CALENDAR

PLANTING CALENDAR FOR TYPE I CLIMATE TWO PRONOUNCED SEASONS : DRY from November to April WET during the rest of the year

All the provinces of the western part of the islands of Luzon, Mindoro, Negros,and Palawan are covered in Type I.

CROP PERIOD CROP PERIODRice: Lowland June - September Muskmelon November - January October - December Okra May - JunePalagad January - February October - DecemberUpand April - June Patola May - June October - JanuaryCorn: Squash May - JuneDry season Ocrober - January October - DecemberRainy season May - June Tomato October - January Upo October - JanuaryPeanut: Watermelon November - JanuaryDry season November - January Rainy season May - June Root: Camote(Sweet May - JuneBeans: Potato) December - FebruaryBatao May - June Gabi May - JuneBountiful Bean May - June Ginger May - June October - December Raddish October - DecemberCowpea May - June Sinkamas October - December October - November Tugue May - JuneCadios May - June Ubi May - JuneMungo July - September Cassava May - June November - February October - DecemberPatani May - June October - January Others: Seguidillas May - June Garlic October - DecemberSitao May - June Onion October - December November - February Sweet Pepper May - JuneSoybean May - June September - December Condol May - JuneVegetables: October - DecemberLeafy: Chayote May - JuneCabbage October - December October - DecemberCauliflower October - February Spinach October - NovemberCelery October - February Sweet Peas October - DecemberLettuce August - January Carrot October - DecemberMustard August - January Potato(Irish) October - DecemberPechay October - December Talinum May - June October - DecemberFruit: Kutchai October - DecemberAmpalaya May - July Arrowroot May - June October - January Tapilan May - JuneCucumber May - June September - October September - December Beets October - JanuaryEggplant May - June Jute May - June September - February Endive September - OctoberMelon October - January Snap Bean October - December

28

PLANTING CALENDARPLANTING CALENDAR FOR TYPE 2 CLIMATENO DRY SEASON with a very PRONOUNCED MAXIMUM RAINFALL from November toJanuary. The areas covered are Catanduanes, Sorsogon, Eastern part of Albay, the Eastern andNorthern parts of Camarines Norte and Camarines Sur, a great portion of the Eastern part of Quezon,the Eastern part of Leyte and a large portion of Eastern Mindanao.

CROP PERIOD CROP PERIOD Rice: Fruit: Lowland October - December Ampalaya June - AugustPalagad May - July November - FebrauryUpand June - August Condol January - March September - November Cucumber March - April Eggplant January - AprilCorn: August - SeptemberDry season March - May Melon(ordinary) March - JuneRainy season January - February Muskmelon March - June August - September Okra Whole year Patola March - SeptemberPeanut: Squash Whole year Dry season Janury - Febraury Tomato January - April August - September August - SeptemberRainy season May - June Upo November - March Watermelon January - MarchBeans: Root: Batao Febraury - April Camote Year Round Cowpea or Kibal January March Carrot March - April May - July Cassava Year Round November - December Gabi Year Round Cadios Febraury - March Ginger Year Round Bountiful Bean January - May Raddish November - DecemberMungo Febraury - June March - MayPatani(climbing) January - May Ubi Year Round Seguidillas Febraury - April Sitao May - June Others: Soybean January - March Irish Potato February - MarchTapilan January - March Endive December - March August October Onion December - March Garlic November - DecemberVegetables: Sinkamas October - NovemberLeafy: Sweet Pepper February - MarchCabbage January - March August - SeptemberCelery January - March Chayote February - MarchKutchai March - July Arrowroot June - SeptemberLettuce March - June Beet January - MarchPechay January - March Peas February - MarchCauliflower January - March Jute January - MarchMustard January - March Talinum June - JulySpinach January - March November - December

29

PLANTING CALENDARPLANTING CALENDAR FOR TYPE 3 CLIMATESeasons are not pronounced, relatively DRY from November to April and WET during the rest ofthe year. This type of climate covers the Western part of Cagayan(Luzon), Isabela, Nueva Vizcaya,the Eastern portion of the Mountain Province, Southern Quezon, the Bondoc Peninsula, Masbate,Romblon, Northeast Panay, Eastern Negros, Central and Southern Cebu, part of Northern Mindanao,and most of Eastern Palawan.

CROP PERIOD CROP PERIODRice: Lowland June - August Mustard May - JulyPalagad November - January October - DecemberUpand April - June Pechay May - June

October - DecemberCorn: Spinach May - JuneDry season October - December October - DecemberRainy season April - June Third Crop December - February Fruit:

Ampalaya May - June Peanut: November - DecemberDry season September October Chayote May - June Rainy season April - June November - JanuaryThird Crop December - January Cucumber May - June October - JanuaryBeans: Eggplant May - June Batao May - June November - JanuaryBountiful Bean May - June Melon(ordinary) May - June November - January October - JanuaryCowpea or Kibal May - June Muskmelon November - January November - December Okra May - JulyKadios May - June October - December October - November Patola May - JulyMungo December - January October - January September - October Squash May - June Patani May - June October - December(climbing) November - December Sweet Pepper May - June Seguidillas May - June October - DecemberSitao May - June Tomato October - January November - January Upo April - MaySoybean May - June October - January October - December Condol June - JulyTapilan May - June November - January November - December Watermelon October - JanuaryPeas April June November - January Root: Vegetables: Sweet Potato April - JuneLeafy: November - JanuaryCabbage April - June Carrot October - December October - December Gabi May - JulyCauliflower October - December October DecemberCelery May - July Garlic October December October - December Ginger October DecemberLettuce April - May November - December October - December Irish Potato October - December

PLANTING CALENDAR

PLANTING CALENDAR FOR TYPE 4 CLIMATERAINFALL more or less evenly distributed throughout the year.The areas covered by Type 4 climate are Batanes Province, Northeastern Luzon, Western CamarinesNorte and Camarines Sur, Albay, Eastern Mindoro, Marinduque, Western Leyte, Northern Negros,and most of Central, Eastern, and Southern Mindanao.

CROP PERIOD CROP PERIODRice: Lowland May - July Lettuce May - June August - October January - FebruaryPalagad November - January Mustard June - JulyUpand April - June September - January

Corn: Pechay May - July

Dry season September - November November - January

Rainy season April - June Spinach April - May

Third Crop November - February Fruit:

Ampalaya May - June

Peanut: September - January

Dry season September - November Chayote May - June

Rainy season May - June November - December

Third Crop November - February May - June

Beans: October - December

Batao May - June Cucumber June - July

Bountiful Bean May - June October - December

October - December Eggplant June - July

Cowpea or Kibal May - June November - January

October - December Melon November - January

Kadios May - July Muskmelon November - JanuaryMungo May - June Okra June - July November - January September - OctoberPatani May - June January - February November - January Patola May - JuneSeguidillas May - June December - JanuarySitao May - June Squash May - June October - January November - JanuarySoybean May - June Sweet Pepper May - June November - January September - JanuaryTapilan May - June Tomato May - June November - December October - JanuaryPeas June - July Upo May - June December - January October - JanuaryVegetables: Watermelon April - MayLeafy: November - JanuaryCabbage June - September Root: October - January Camote May - JuneCauliflower April - July September - November September - January Carrot May - JuneCelery June - July November - January January - Febraury Gabi June - SeptemberKutchai June - July January - February

TABLE OF CONTENTS

Section Title Page

1.0 GENERAL 1

2.0 DAM 12.1 Determination of Dam Height 12.1.1 Dead or Inactive Storage 12.1.2 Active Storage 32.1.3 Flood Surcharge 32.1.4 Freeboard 62.1.5 Outline of Dam Height Computation 72.2 Dam Crest Width 72.3 Selection of Type of Earth Dam 72.3.1 Homogeneous/ Modified Homogeneous Type 72.3.2 Zoned Embankment Type 92.4 Embankment Slopes 112.5 Seepage Through Earth Embankment 132.5.1 Seepage Line 132.5.2 Position of Seepage Line 132.5.3 Quantity of Seepage 132.5.4 Filter Design 212.6 Embankment Slope Protection 222.6.1 Upstream Slope 222.6.2 Downstream Slope 23

Section Title Page

3.0 SPILLWAY 243.1 General 243.2 Spillway Type and Alignment 243.3 Spillway Hydraulics 243.3.1 Control Section 253.3.2 Discharge Channel 253.3.3 Terminal Section 313.4 Structural Requirements 40

4.0 OUTLET WORKS 434.1 General 434.2 Specific Type and Physical Arrangement 434.3 Outlet Works Hydraulics 444.3.1 Section of Design Discharge Head Combination 444.3.2 Sizing of Discharge Pipe 444.3.3 Sizing of Impact Type Dissipator 484.4 Structural Design Considerations 48

5.0 IRRIGATION WORKS 515.1 General 515.2 Canal Layout and Profile 515.3 Canal Hydraulics 515.3.1 Slide Slopes 515.3.2 Permissible Velocity 525.3.3 Applicable Formula for Sizing of Canal 525.3.4 Freeboard 535.4 Design of Canal Structures 53

Appendix I General Design Criteria for Canal Structures 55

LIST OF TABLES

Table No. Title Page

1 Outline of Dam Height and Dam Crest 8

2 Embankment Slopes for Homogeneous Dams 14

3 Embankment Slopes for Zoned Dams 15

4 Permissible Velocities for Non-Cohesive Soils 27

5 Permissible Velocities for Grassed Channel 28

6 Outline of USBR Basin Computations Format 46

7 Cantilever Retaining Wall Parameters 41

8 Discharge Pipe Computations Format 46

9 Impact Type Stilling Basin Computations Format 50

LIST OF FIGURES

Figure No. Title Page

1 Reservoir Storage Allocations 22 Reservoir Operation Studies Format and Flow Chart 43 Flood Routing Format and Flow Chart 54 Modified Homogeneous Dam Sections 105 Size of Impervious Core of Zoned Dam 126 Slope Stability Chart No. 1 167 Slope Stability Chart No. 2 178 Slope Stability Chart No. 3 189a Elements of Seepage Line 199b Diagrams for Determining ∆a and a 2010 Flow Profile Along Spillway 3011 Unsubmerged Deflector Bucket 3212 Type IV USBR Basin 3313 Type III USBR Basin 3414 Type II USBR Basin 3515 Hydraulic Jump Nomograph

(Stilling basin Depth Vs Hydraulic Head for Various Channel Losses) 39

16 Typical Chute and Stilling Basin Section 4217 Typical Outlet Works System 4518 Impact Type Energy Dissipator 4919 Types of Irrigation Canal Layout 54

ENGINNERING DESIGN

1.0 GENERAL

For the Water Impounding Component of the Rainfed Project, the earth embankment dam type (homogeneous or zoned type) is considered to be more cost effective over concrete or other types of dam. The dam embankment volumes, consisting of natural earth materials, are relatively small and are available at or in the vicinity of the project site. These materials are soil and rock in their many varied forms.

Included in this section are the procedures, criteria and assumptions used in the design of a small earth dam and its appurtenances.

Also included in the later part of this section are the procedures, criteria and assumptions in the design of irrigation works consisting of canals and canal structures as well as access roads to complete the coverage on the physical structural component of the project.

In the procedures and assumptions that follow, it is assumed that dam location, necessary site investigations as well as prerequisites studies on geology, hydrology, etc., have already been undertaken.

2.0 DAM

2.1 Determination of dam Height

In general, the height of the dam is determined on the basis of the following vertical space requirements in the reservoir.

a. Dead or Inactive Storage Spaceb. Active Storage Spacec. Flood Surcharged. Freeboarde. Settlement

Space allocations of each of the above items are illustrated in Figure 1.

2.1.1 Dead or Inactive Storage

The number of years for sediment to fill up the dead storage space plus about 20% of the live storage is termed as the expected “economic life” of the project. This time magnitude is an agency policy decision.

1

Unless amended later, sediment volume shall be computed on the basis of 25 years of accumulation in the reservoir. This volume shall be allocated in the dead storage space as shown in Figure 1.

2.1.2 Active Storage

The active storage is allocated primarily for irrigation purposes. This space is determined from reservoir operation studies.

Reservoir operation study basically “water accounting”. No clear-cut formula is involved but the basic principle is to optimize reservoir to meet water requirement.

The study involves trial runs for different hectareage of service area until maximum area is attained with minimum reservoir spill or shortage.

Among the data and assumptions needed to undertake the reservoir operation study are the following:

a. Reservoir inflowb. Reservoir evaporation lossc. Water requirementsd. Reservoir area-capacity-elevation curves.e. Reservoir elevation at the end of the operation must be equal to the starting elevation.

Items a, b and c are obtained from the results of Hydrologic Studies. Item d is derived from a reservoir topographic map.

Shown in Figure 2 are the typical format and detailed flow chart for reservoir operation studies.

2.1.3 Flood Surcharge

Flood surcharge space is allocated for the design flood.

Maximum surcharge height is the difference between maximum and normal water surface. It is dependent on three factors namely;

a. Spillway size opening.b. Reservoir capacity-elevation relationship.c. Magnitude and shape of the inflow hydrograph.

Flood surcharge height is estimated by flood routing.

3

There are a number of methods for flood routing but the basic formula is:

I = O + S ----------------------------------------- 1

Where; I = inflow volume O = outflow volume S = change in storage

A simple and expedient method of flood routing is by arithmetic trial and error.Shown in Figure 3 are format and detailed flowchart for such method.

In this all other methods of flood routing, it is assumed that all outlets are fully closed and all discharges are allowed to pass only over the spillway. Moreover, water surface in the reservoir is at normal level at the start of the flood.

The data required to undertake flood routing computations are the following:

a. Hydrograph of inflow design flood.b. Reservoir capacity-elevation curve.c. Spillway rating curve or equation given by the following formula for a broad-

crested weir:

Q = CLH3/2 ------------------------------------------ 2

Where: Q = discharge over the spillway C = weir coefficient; 1.704 metric H = surcharge height L = spillway width

2.1.4 Freeboard

Freeboard space is provided against wave splash along the upstream face of the dam, which may coincide with occurrence of the design flood as well as embankment settlement. It is estimated by the following formula:

For vertical wallFb1 = --------------------3Fb2 = 2% to 5 % of dam height ------------------------------------------- 4Fb = Fb1 + Fb2 ------------------------------------------------------------------5

Where: F b1= freeboard due to wave run-up, m F = reservoir effective fetch, km V = wind velocity, km/hr Fb2 = freeboard due to embankment settlement, m Fb = total freeboard, m

6

swip manual part 1

Documents

estimation of water

soil moisture storage

estimation of watershed

estimation of runoff

water management diliman

optimum storage drainage

water management scheme

unadjusted tl tl