MANUAL FOR AGROHYDROLOGY AND ENGINEERING DESIGN FOR SMALL WATER IMPOUNDING PROJECT (SWIP) Department of Agriculture BUREAU OF SOILS AND WATER MANAGEMENT Diliman, Quezon City March 1997 TABLE OF CONTENTS DESCRIPTION 1. ESTIMATION OF RUN-OFF and DERIVATION OF INFLOW 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 2. Establishment of Project Data Estimation of Basin Lag Time and Time Concentration Computation for Rainfall Depth Rainfall Increments Determination Rearrangement of Rainfall Pattern Derivation of Synthetic Unit Hydrograph Convolution of Equation for Flood Hydrograph PAGE NO. HYDROGRAPH 1 1 2 2 3 8 9 10 10 10 11 11 14 14 14 14 14 15 16 16 16 FIELD WATER BALANCE COMPUTATION 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 Establishment of Cropping Pattern and Cropping Calendar Computation of 80% Dependable Rainfall Crop Coefficient and Crop Rooting Depth Percolation Loss Soil Water Holding Capacity Actual Evapotranspiration Change in Storage Initial Storage Estimation of Water Storage at End of Decade Irrigation Efficiency 3. ESTIMATION OF 10-DAY RESERVOIR INFLOW 3.1 3.2 4. ANNEXES A. B. C. D. Philippine Water Resources Region Climate Map of the Philippines Monthly Distribution of Potential Evapotranspiration of Selected Places in the Philippines Planting Calendar Estimation of 10-Day Inflow for Region I, II, & IV Estimation of 10-Day Inflow for Other Regions 24 25 27 28 LIST OF TABLES TABLE NO. Regression Coefficients of the Rainfall Intensity-Duration Frequency Curve for Different Locations 2 3 4 5 6 7 8 9 10 Soil Groups for Estimation of Watershed Index W. Antecedent Moisture Condition for Estimation of Water Index W. Values of Watershed Index W. Adjustment of Watershed Index W for Antecedent Moisture 7 Recommended Retention Rate for Hydrologic Soil Groups T/Tp versus q/qp for Dimensionless Hydrograph Percolation for Different Soil Types S W H C of Different Soil Textural Class Regional Run-off Coefficient and % Monthly Baseflow Distribution 4 6 6 6 Condition 8 9 12 15 17 PAGE NO. LIST OF FIGURES FIGURE NO. 1 1 2 4 5 6 TITLE Rearrangement of Rainfall Increments Water Management Scheme and Crop Depending Variables for Field Water Balance for Irrigated Wetland Rice. Crop Depending Variables for Field Water balance of Irrigated Corn. Crop Depending Variables for Field Water balance of Irrigated Mungo. Crop Depending Variables for Field Water balance of Irrigated Tomato. Crop Depending Variables for Field Water balance of Irrigated Peanut. PAGE NO. 5 12 12 13 13 14 b. Field Water Balance Computation 3. Total fall (elevation difference) from highest ridge to outlet.2. TC. f. Estimation of Run-off and Derivation of Inflow Hydrograph (25 yrs. a. in miles LC = mainstream length from outlet to the nearest basin centroid. e. Tp and peak runoff. Watershed cover/land use. These are as follows: 1. Adjust estimate of TL Adjusted TL (for ∆D = 0. These are topographic map soil and land capability mp or report. land use/vegetation map or report and rainfall intensities.72 for foothill drainage area 0. Soil type of watershed (dominant) to determine the soil group identified soil type in the watershed belong to.2 for mountatins drainage area 0. Time to peak. Mainstream from outlet to point nearest basin centroid. ESTIMATION OF RUN-OFF AND DERIVATION OF INFLOW HYDROGRAPH This would require the following data and inputs to be taken from the project site.) 2. Compute for unadjusted TL (TL in hours) Where: L = mainstream length from outlet to highest ridge. 1. A. Reservoir Inflow Computation 1. in hours. Lc. Drainage Area. . c. Y = watershed gradient a = 0. Compute time of concentration. 1.35 for valley drainage area b. TL and time of Concentration TC using Snyder’s Method (revised). in meter. in sq. g. L.4 ≠ ) Adjusted TL = TL + ¼ (∆D ) Method.1 Establishment of the Project Data a.38 Ct = coefficient with values (Linsley’s): 1. the Estimation of Basin Lag Time. Watershed gradient. qp. H. The following arranged procedures would be helpful in deriving the inflow hydrograph.AGROHYDROLOGIC STUDIES AND ANALYSES There are 3 general computations to be considered in the study. km. and 1 c. Mainstream length from outlet to highest ridge. d. 3 Compute for rainfall Depth P for different duration D. in cms/mm excess rainfall: qp = Where: A = drainage area.) where Tc < 3. mm in 2/3 Position of peak pi . Frequency Curve for different location in the Philippines (Table 1).TC = TL / 0. No. 3. 1 2 3 n Rainfall Depth P. qp = cms/mm 1. Hr D1 = ∆D D2 = 2D1 D3 = 3D1 Dn = 2Dn Rainfall Intensity I.70 d. Considering that the highest qp is usually computed or obtained from the 2/3 time position pattern. sq. i = n/3 Peak ∆P1 at 2/3 time position. utilizing equation: P = iD where i = rainfall intensity computed using Rainfall Intensity Duration. thus tabulation would only be as follows: 2 Rainfall Increments Rearranged Rainfall Increments APi. 2. km. i= 2n/3 + 1 The sequences for peak at the different positions mentioned are shown in figure I. 1 hr. Equation : D = Duration The tabulation of rainfall depth Pi versus Duration Di is thus: Seq. Compute the Peak rate of Runoff. Compute the time to peak. mm P1 P2 P3 Pn Obtain rainfall increments ∆Pi and rearranged them according to three maximization patterns: 1.4 Duration. the hydrograph to be derived will utilize this pattern without anymore working the other 2 patterns for comparison. Tp using Tp = ½ ∆D + TL (adjusted) Where: ∆D = time duration of one inch of excess rainfall (USDA SCS) suggested values of ∆D as 0. 1 2 4 n 1. e. where 3<Tc<6:1/5 Tc where Tc>6.5 hr. (or 0. i = n/2 Peak ∆P1 at 1/3 time position. Peak ∆P1 at middle time position.40 hr. min/hr. D. Gen. TL = time lag (adjusted). hr. qp. No. Table 4 Value of W for different land uses/covers.2s Where: Ia = initial abstraction.5 For the rearranged rainfall pattern considered. Applicable values are given in Table 6. f (mm/hr) – Duration. and land use cover in the watershed . ∆P8 = P8 – P7 ∆P5 9. also called the runoff curve number N or CN = function of soil group. ∆P12 = P12 – P11 ∆P4 13. 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. assuming AMC II) and Table 5 (Adjustments of W for AMC I and AMC III). ∆P1 = P1 ∆P14 2. . ∆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. ∆P2 = P2 . T Curve for Different Locations: General Equation: i = aTC . antecedent moisture condition (AMC). 1. Ia: Ia = 0. in inches s = 1000 – 10 W = maximum potential difference between rainfall and runoff. in inches W = watershed index. 1.P1 ∆P13 3. ∆P14 = P14 – P13 ∆P11 15. -Apply the Soil Conservation Service (SCS) Method to obtain Initial Abstraction.Refer to Table 2 (Soil Group). ∆P6 = P6 – P5 ∆P7 7. ∆P5 = P5 – P4 ∆P9 6. ∆P7 = P7 – P6 ∆P6 8. ∆P11 = P11 – P10 ∆P1 12. Table 3 (Antecedent Moisture Conditions. ∆P3 = P3 – P2 ∆P12 4.________________________________________________________________________ Seq. ∆P9 = P9 – P8 ∆P3 10. 3 TABLE 1 Regression Coefficients if the Rainfall intensity.After subtracting Ia. ∆P10 = P10 – P9 ∆P2 11. ∆P4 = P4 – P3 ∆P10 5.The computed initial abstraction Ia is subtracted from the rainfall over the necessary initial number of time increment until Ia is satisfied. . ∆P13 = P13 – P12 ∆P8 14. t (hr) Frequency. 9968 0. Surigao del Sur Davao City a 47.30 0. MIA Pot Area.9972 0. Cagayan Aparri.577 0.486 57. Pampanga Dagupan. Quezon Alabat.620 0.9901 0.85 0.1740 d 0.9981 0.487 0.2020 0. Arayat.30 0.553 55.2280 0. Pampanga Gabaldon.20 0.057 0. Samar Catbalogan. Quezon Ambalong.80 0.2337 0.9944 0.690 0. Rizal Daet.20 0.10 0. Pampanga Sta.511 0.960 62.9916 0. Mondoro Or.2090 0.591 0.1680 0. Cagayan San Agustin.812 1.40 0.836 49.9942 0. Camarines Norte Legaspi.621 61.30 0.571 78.2220 0.327 54.10 0.9958 0.330 100.821 51. Batangas Angono. Quezon Casiguran.9956 0.314 44.2460 0.105 39.461 0.1340 0. Apalit.2310 0.2520 0.1395 0.846 46.491 0.9620 0. Tanauan.60 0.40 0.591 0.2310 0.577 0.10 0.414 60.609 0.209 67.676 47.9969 0.611 0. Leyte Zamboanga City Cagayan de Oro Surigao City Binatuan.9971 0.9986 2 3 4 5 6 7 8 9 10 11 .9979 0.754 0.670 0.9973 0.503 48.(t+b)d REGION 1 STATION/LOCATION Vigan.575 0.2150 0.1660 0.863 58.2330 0.602 0.70 0.9932 0.448 0.351 62.9973 0. Manila Tayabas.20 0.687 53. Quezon Calapan.9992 0.629 0.9950 0.9849 0.20 0.9951 0.9976 0.295 51.424 41.20 0.598 0.961 36.10 0.710 77.1910 0.2300 0. City Virac.9905 0.1940 0.679 0.10 0.343 0.9958 0.9880 0.587 55.20 0.1320 0.803 0.9800 0.9962 0.433 81.2400 0.630 0.40 1. Samar Tacloban.2780 0.959 b 0.9912 0.00 0.9882 0.263 53.570 0.2380 0.661 48.889 51.2040 0.9949 0. Lingayen Iba.10 0.70 0.681 0.610 0.2020 0.9934 0.1950 0.617 0.052 44. Catarman.768 0.2220 0.2290 0.2240 0. Eastern Samar UEP.665 0.50 c 0.1980 0.611 0.890 51.10 0.749 41.554 0. Ilocos Sur Baguio City Laoag City Tuguegarao.15 0. Cruz.798 39.2710 0.30 0.9973 0. Pangasinan Matalava.390 59. Nueva Ecija Infanta.9970 0.9867 0.20 0.568 0.622 61.2370 0.2480 0.2010 0.945 R 0. Catanduanes Iloilo City Cebu Airport Dumaguete City Borongan.2370 0.597 43.581 0.1340 0.40 0. Zamabales Cabanatuan City Cansinala.9963 0.9959 0.9948 0.10 0.50 0.954 0.2480 0.717 0. 4 .Note: If b resulting rainfall intensitydurationfrequency are straight (plotted on log chart). Ø the curves lines log. 5 TABLE 2: Soil Groups for Estimation of Watershed Index W . 0. Light soils under/or well structured soils having above Average infiltration when thoroughly melted.1 in. particularly days of high swelling capacity. deep sands with little silt or clay. 1. For Example.1 in. silty loams.1 in.1 in. For example. Growing Season lass than 1. light sandy loams. For example. For example.Soil Group A B C D Description of Soil Characteristics Soils having very low runoff potential. Antecedent Moisture Condition (AMC) I II III TABLE 4: Values of Watershed Index W (Assuming Antecedent Moisture Condition II) Farming Treatment Hydrologic Condition Poor Fair Good Poor Fair Good Good Straightro w Contoured Poor Good Poor Good Poor Good Poor Good A 70 50 40 45 35 25 30 65 60 65 55 65 70 70 65 80 6 SOIL GROUP B C 80 85 70 80 60 75 65 75 60 75 55 70 60 75 70 75 70 75 80 80 75 85 70 85 80 80 80 85 85 85 80 90 D 90 85 80 85 80 75 80 90 85 85 85 90 90 90 85 95 Land Use or Cover Native pasture or grassland Timbered Areas Improved Permanent pastures Rotation pastures Crop Straightro w Contoured Fallow - (Table 4 Con’t) . TABLE 3: Antecedent Moisture Conditions for Estimation of Watershed Index W Rain in pervious 5 days Dormant Season less than 0.5 in. Soils having high runoff potential.4 to 2. and very shallow soils underlain by dense clay horizons. clay loams. more than 1.5 – 1. heavy soils. Medium soils and shallow soils having below-average Infiltration when thoroughly melted. more than 2.4 in. Native pastures: Pastures in poor condition is sparse. with considerable undergrowth. Crops: Good hydrologic condition refers to crops which form a part of a well planned and managed croppasture-follow rotation. Pasture in good condition is lightly grazed and with more than three-quarters of the catchment area under plant cover. Rotation pastures: Dense. b. overgrazed or “opportunity” pastures are considered to be poor condition. Pasture in fair condition is moderately grazed and with between half and three-quarters of the catchment under plant cover. moderately grazed pastures used as part of a well planned. Good areas are densely timbered and ungrazed. e. heavily grazed pastures with less than half the total watershed area under plant cover. TABLE 5: Adjustment of Watershed index W for Antecedent moisture Condition AMC = II 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 Corresponding Value of W for: AMC = I 100 87 80 70 65 60 50 45 40 35 30 25 20 20 15 10 AMC = III 100 99 98 97 95 90 90 85 80 75 70 65 60 55 50 45 7 . c. Sparse. Poor hydrologic condition refers to crops managed according to a simple cropfollow-rotation. Fair areas are moderately grazed. d. crop-pasture-fallow rotation are considered to be in good hydrologic condition.The meaning of the terms listed under the heading “Hydrologic Condition” are as follow: a. Improved permanent pastures: Densely sown permanent legume pastures subject to careful grazing management are considered to be in good hydrologic condition. with some undergrowth. Timbered areas: Poor areas are sparsely timbered and heavily grazed with no undergrowth. hr ∆D 2∆D 3∆D 4∆D n∆D Dimensionless T/Tp ∆D/Tp 2∆DTp 3∆D/Tp 4∆D/Tp n∆D/Tp Hydrograph q/qp Values interpolated From Table 7 Unit Hydrograph Ui = (q/qp) i qp (q/qp)1 qp (q/qp)2 qp (q/qp)3 qp (q/qp)4 qp (q/qp)n qp Σ Ui Cms/mm Uu = Ui/ki Uu1 Uu2 Uu n Σ Uu 8 . ) Uu (Corrected Ui) = original Ui K -To check. i 1 2 3 4 n Time T.001 time etc. 2∆D .6 Σ U1 ∆D D in hours. km. 3 . -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. A in sq. . 2. K should be equal to one when using the same formula: K = 3. .TABLE 6: Recommended Retention Rate for Hydrologic Soil Group (USBR) Hydrologic Soil Group A B C D 1. 3∆D TP TP TP Until q/qp is less than 0. . . 3 . 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 ratio equal to T/Tp = ∆D .12 0. inches/hour 0.04 Derive the synthetic unit hydrograph.6 Retention Rate. qp = Computed peak rate of runoff in cms/mm -Obtain correction factor k for synthetic unit hydrograph (Dimensionless and ideally close to 1: K = 3.6 Σ U1 ∆D A -In tabulated form we will have: Seq.) A -Correct to ordinate Ui ( i = 1. ) q/qp I = interpolated value of q/qp from smooth dimensionless hydrograph.4 0. No. 2.24 0. 5 5 Infinity Disch.3 1.036 0.56 0.7 To the rearrange pattern of excess rainfall.13 0. 3 .89 0.84 0.5 1. Ratio q/qp 0 0.TABLE 7: Time Ratio T/Tp 0 0.24 0.1 0.8 3 3.8 2 2.6 0.43 0.97 1 0.75 Time Ratio T/Tp 1.098 0.4 2.32 0.6 2.18 0. 2.77 0.66 0.1 1.28 0.7 0.6 1.009 0.175 0. \ 9 .92 0.42 0.2 1.018 0.4 0.2 2.98 0.16 0.4 T/Tp versus q/qp for dimensionless hydrograph Disch.004 0 1. apply the synthetic unit hydrograph Qi ( i = 1.2 0. Ratio q/qp 0.6 0. .3 0.075 0.9 1 1. . ) 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.015 0.8 0.5 0.5 4 4. - Feb. . 2. 36 __ SK = 1 Σ (XKi . Where c. . . . . . . . .831 . .36 d. . 1 2 3 . FIELD WATER BALANCE COMPUTATION Establish the best cropping pattern and cropping calendar with the following objectives: a) minimum irrigation requirements. . . 3 . Dec. b) maximum annual production. . . 3 . Compute the standard normal deviation corresponding to an axceedance probability. . . Collect 10-day rainfall data. .2. . . . . Compute the mean of 10 – day rainfall for all decades K = 1. . To compute for 80% dependable for a given site the following procedures are to be considered: a. . . . . 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. . 3. N Mean Std. . 2. . . . . . . . . . defined as the sums of daily rainfall over each defined 10day period and arrange them as follows: Year Month Jan.X )2 N-1 i=1 Where SK = standard deviation of 10 – day rainfall in decade K …. . . . . Decade 1 2 3 4 5 6 34 35 36 b. Dev. for p = 80% tp = -0. . . p of 80 %. . . . . . Fill the column for the rainfall (rain) with 80% dependability computed using the two parameter lognormal distribution and the average potential evapotranspiration (PET). . Compute the standard deviation of 10 – day rainfall for decades K = 1. 10 Compute the coefficient of variation of 10 – day rainfall for all decades K = 1. 2. 36 N XK = 1 Σ XKi N i =1 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. tp. . . Where ZK = coefficient variation e. . . . . . . Compute the 10 – day rainfall at 80% dependability for all decades _ RK = XK + SK KK Where: RK = 10 – day rainfall at 80% dependability h. ZK .1. 36 Where: B = Ln ( 1 + Z2 ) KK = frequency factor in decade K g. - Dec. RK . . 11 TABLE 8: Percolation For Different Soil Types Clay --------------------------------------------------------------------------------. . Mean 80% dep or 10 – day rainfall at project site Fill. . . . Refer to Figures 2 to 6. = SK . 2. Compute the frequency factor for all decades K 1. . Month Jan. KK . . 3. Make a reasonable assumption for probable percolation losses (mm/day) or refer to Table 8. .f. . Tabulate the results as follows: Decade 1 2 3 . the crop coefficient at all stages can be assumed equal to one (1). 34 35 36 XK . For wetland rice. . .up the crop-coefficients (kc) and crop-rooting depth columns according to the establishment of cropping calendar and crop growing stages. . . .25 mm / day . 85 600 6 0.50 mm / day 1.9 775 8 0.75 900 11 0.5 900 12 FIGURE 4 Crop Depending Variables Used in the Field Water Balance For Irrigated Mungo .0 mm / day Water Management Scheme & Crop Depending Variables Used In Field Balance Computation For Irrigated Wetland Rice Land Soaking 1 2 Land Preparation 3 4 5 6 7 Crop in the Field (100 Days) 8 9 10 11 12 13 Rainfall Collecting Period 1 Maximum water depth in paddy. mm Minimum water depth.9 825 9 0. mm Optimum water depth.8 450 5 0.9 700 7 0.7 5 300 4 0.9 875 10 0. mm FIGURE 3 200 10 100 2 80 20 65 3 80 20 65 4 5 6 80 20 50 7 80 20 50 8 80 20 50 9 80 20 45 10 80 20 45 11 80 20 45 12 10 0 0 13 0 0 0 80 80 20 20 50 50 Crop Depending Variables For Field Water Balance For Irrigated Corn Crop in the Field (110 Days) 1 2 3 4 5 6 7 8 9 10 11 Rainfall Collection & Land Preparation LP LP Crop Coefficient Rooting Depth (mm) 1 0.Silty Clay --------------------------------------------------------------------------Clay Loam-------------------------------------------------------------------------Silty Clay Loam-------------------------------------------------------------------Sandy Clay Loam-----------------------------------------------------------------Sandy Loam-----------------------------------------------------------------------Figure 2: 1.0 mm / day 4.75 mm / day 2.65 100 2 0.75 mm / day 1.65 200 3 0. 77 700 8 0.85 600 7 0.5 150 3 0.35 80 2 0.Rainfall Collection & Land Preparation LP 1 2 3 Crop in the Field (80 Days) 4 5 6 7 8 LP Crop Coefficient Rooting Depth 1 0.9 300 6 0.85 300 7 0.7 700 FIGURE 6 13 Crop Depending Variables for the Field Water Balance for Irrigated Peanut Rainfall Collection .9 300 5 0.35 80 2 0.7 300 4 0.5 100 3 0.9 500 6 0.77 300 8 0.7 300 FIGURE 5 Crop Depending Variables Used in the Field Water Balance for Irrigated Tomato Rainfall Collection & Land Preparation LP 1 2 3 Crop in the Field (80 Days) 4 5 6 7 8 LP Crop Coefficient Rooting Depth (mm) 1 0.9 400 5 0.7 230 4 0. 8 2.9 5 350 7 0. Ø If STORi < allowable minimum storage Then IRRIGATION = Optimum Storage – STORi STORi = Optimum Storage Drainage = Ø.5 5 600 2.7 0 200 4 0. Ø DRAINAGE = Ø. soil moisture storage is usually assumed to 50% of soil water holding capacities in the root zone. that is 0. Do not irrigate during the last two decade of a given period.AET . (10% . allowable min.PERCO .54 (WHC) (ROODEP).6 2. Actual evapotranspiration (AET) is equal to AET = PET x KC Change in storage (ΔSTOR) is equal to STOR = RAIN . .7 600 10 0.70) for paddy rice INIT = (Raini + Raini – 1) (0.9 300 6 0. Ø 14 2. Ø ELSE IRRIGATION = Ø.& Land Preparation LP 1 2 Crop in the Field (100 Days) 3 4 5 6 7 8 9 10 LP Crop Coefficient Rooting Depth (mm) 0 1 0. Initial Storage (INIT) is estimated using the following formula INIT = (Raini + Raini – 1) (0.7 2. Refer to Table 9.4 80 2 0.5 Make a reasonable assumption of soil water capacities WHC in volume percentage of soils used for upland crops.7 5 500 9 0.20%).7 5 400 5 8 0.9 Note: For upland crops.AET for upland crops.7 0 150 3 0.50) for upland crops Estimate the water storage (STOR) at the end of a given decade: STORi = STORi – 1 + ΔSTOR If STORi > allowable max storage Then DRAINAGE = STORi – allowable max storage STORi = allowable max storage IRRIGATION = Ø.for paddy rice STOR = RAIN .9 5 250 5 5 0. Soil Water Holding Capacities of Different Soil Textural Classes: Total Available Moisture Pv =Pw As Volume% 8 (6-10) 12 (9-15) 17 (14-20) 19 (16-22) 21 (18-23) 23 (20-25) TABLE 9 Soil Texture Sandy Sandy Loam Loam Clay Loam Silty Clay Clay 15 3. IV. 10 – day reservoir inflow are estimated as follows: .2. III.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. characterized by distinct wet and dry seasons. 3.1 ESTIMATION OF 10 – DAY RESERVOIR INFLOW For Regions I. (sq. equal to estimated mean monthly runoff coefficient Pj = 80% dependable rainfall b. km.) 10 – day Baseflow Qj = Where: Qj = DQj = BFj = DQj + BFj reservoir inflow in decade j (mm) direct runoff in decade j (mm) baseflow in decade j (mm) c. 10 – day Direct Runoff DQj = RCj . = regression factor for the region where the project is located (Table 10) D.026 (D.) where DA is drainage area in sq.Qj – 1 Where: BFj = baseflow in decade j (mm) F = 10 – day reservoir factor = 0. (This regression equation analysis of several small watersheds <100 km2 In the country). Where: DQj = RCj .2 For the other regions in the country which are predominantly characterized by indistinct. equal to estimated monthly runoff coefficients Pj = mean 10 – day rainfall in decade j (mm) b. = Drainage Area.002 + 0. 10 – day Baseflow BFj = F . Annual Baseflow BF = a + b . or no dry season with more or less continuous rainfall.A. DA Where: BF = annual baseflow a. 10 – day reservoir inflow are estimated as follows: a. Pj Where: DQj = direct runoff in decade j (mm) RCj = runoff coefficient in decade j. Qj – 1 = Total runoff (or inflow) in the previous decade (j-j). TABLE 10 Region 1 16 Regional Run – off Coefficient and % Monthly Baseflow Distribution: . 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.b.A . mm c. km. Pj DQj = direct runoff in decade j (mm) RCj = runoff coefficient in decade j.a. short. RC 0.72 x 10-1 17 Region 3 Month Jan.05 0.75 0.64 0. Dec.67 0. Mar. Dec.91 7.42 7.021 : BF = a + b (D.76 7.A) R = 0.39 8.37 0.43 10.41 0.17 0.17 0.37 10. May June July Aug.25 Region 2 Month Jan. RC 0.7 6.44 0.2 0.off Coefficient.84 9.08 0. Apr. Run .03 0.03 0. Sept. May June July Aug. Nov.off Coefficient. %Baseflow 8.Month Jan.45 .25 0. Sept. Oct. Run . Apr. Feb.18 9.61 0. Nov.17 0.22 7.off Coefficient.08 0 0.05 6.17 0. RC 0. Oct.74 b = -9.37 Linear Curve Fit a = 286. Mar. Feb.72 Run .75 0.34 0.4 0. Oct.15 0.5 Run .3 0.Feb. Feb.5 0.08 0.38 0. Sept.5 %Baseflow 9.7 0. Mar. Apr.47 0.31 8. Nov. Mar.69 8.64 7. Region 5 Month Jan.91 7. Dec. Nov. Sept. Nov.53 8.08 8. Apr. RC 0.off Coefficient. Dec.off Coefficient.44 0.75 0.08 0 0 0. Sept. Region 4 Month Jan.25 0.A) b = 18. May June July Aug.off Coefficient.33 0.19 0.87 Region 6 Month %Baseflow Run .35 0. RC 0.24 0. Dec.19 0.15 0. Mar.28 18 Run .19 0 0 0.7 0.07 BF = a + b (D. Oct.47 R = 0.86 8. 057.79 9.17 8.34 0. Linear Curve Fit a = 2.39 0.66 7. Apr.45 0.58 0. May June July Aug.31 : 0. Oct. May June July Aug.28 7.57 0.4 0.15 0.26 0. RC .1 0. Feb. 043. Nov. Feb.37 8.3 0.A) b = 8.23 8. 055.96 8.A) b = 11.44 0.19 0.Jan.65 Region 7 Month Jan.21 = a + b (D.85 : BF : BF 8. Apr.15 0. Dec.29 = a + b (D.26 R = 0.37 8.695 %Baseflow 8. Sept.1 7.766 19 Region 8 Month %Baseflow Run .80 Run . Mar.3 0. Linear Curve Fit a = 1.45 8.15 0.39 R = 0.07 8.22 8. RC 0.06 8. Mar.33 0.18 0. May June July Aug.26 8. Sept.26 0.16 0.49 0. Linear Curve Fit a = 1. May June July Aug. Oct.45 8. Feb.66 8. RC .1 8.1 0 0.44 0.off Coefficient.09 0.16 0.09 8.6 8.23 8.16 0.35 8.66 8.3 0. Nov. Apr.57 8.39 0.47 8.3 0.39 0.73 8. Dec.47 8. Oct.221 0.3 0.off Coefficient. 24 0.76 = a + b (D.872 Region 9 Month Jan. May June July Aug.42 8.Jan.1 7.37 : BF %Baseflow 8.52 : BF 9.6 7. Sept.16 7.34 0.051 R = 0. Apr.14 0. May June July Aug.19 8.7 7. Dec.3 0.3 b = 30.4 9 = a + b (D.8 8.off Coefficient.51 0.9 8.94 8 8.32 8. RC 0.28 0.3 8. Linear Curve Fit a = 12. Oct.38 0.22 0.3 0.6 8.9 7.7 b = 14.7 7.25 0 0.53 8.22 0. Mar.53 8.14 0. Dec. Linear Curve Fit a = 1.08 0 0 0. Feb.33 8.14 0. Nov. RC . Feb. Oct.1 8.7 0.34 0.14 0.A) R = 0. 164.13 8. Nov. Apr.off Coefficient.07 0.36 20 Region 10 Month %Baseflow Run .66 8.999 Run . Sept.24 0.A) 0. Mar. RC .24 0.27 8.3 8.27 8.4 8. Oct. Feb.25 8.29 8.562 Region 11 Month Jan.39 = a + b (D.53 21 Region 12 Month %Baseflow Run .12 0.90 : BF 8.21 8.32 0.37 8.38 8.751 Run . Linear Curve Fit a = 152.15 0. 119.51 8.26 0. Feb.49 0.24 0.36 8.28 0. Dec.42 8. Sept.A) 0. Nov.3 8.26 0.09 R = 0. Linear Curve Fit a = 2. Apr.49 = a + b (D. Apr.15 0. May June July Aug.31 8.608 : BF %Baseflow 8.43 8. Dec.23 0. Oct. May June July Aug.12 0.21 8. RC 0.35 8. Sept.4 0.25 0.17 0 0 0 0.off Coefficient.34 8.52 b = 6.32 8.3 8.15 0. Mar.off Coefficient.Jan. Mar.29 0.22 b = 7.29 0.34 8.37 0. Nov.16 8.A) R = 0. 4 8.99 8.21 0. Mar.54 8.A) 0. Dec.39 8.45 0.25 0. Sept.44 0. Feb.13 7.13 8. Oct. Nov.66 8.915 22 .26 = a + b (D.21 0.21 b = -4.61 : BF 8. Apr. May June July Aug. Linear Curve Fit a = 1.45 0.24 8.53 8.018 R = 0.13 0.03 8. 751.45 0.69 8.Jan.12 0 0.35 0. 23 . Bohol. the sub-province of Guimaras. Zamboanga del Sur and Zamboanga del Norte together with Sulu Archipelago. 11 – SOUTHEASTERN MINDANAO Davao del Sur. Batangas. Lanao del Sur. Province. Predominant Climate : Type I and Type III Water Resources Region No. Bukidnon and Lanao del Norte. Nueva Viscaya. 5 – BICOL Camarines Norte. Benguet. Predominant Climate : Type II Water Resources Region No. Bulacan. Tarlac. Cavite. Ilocos Sur.ANNEX A – I PHILIPPINE WATER RESOURCE REGIONS Water Resources Region No. Pamapanga. 3 – CETRAL LUZON Nueva Ecija. Mindoro. and the island provinces of Marinduque. 9 – SOUTHWESTERN MINDANAO Misamis Occidental. Camarines Sur. Bikidnon. 10 – NORTHERN MINDANAO Agusan del Norte. Quirino and parts of Mt. North Cotabato. Sorsogon in the South-eastern Peninsula of Luzon and the of Catanduanes and Masbate. Predominant Climate : Type IV Water Resources Region No. 8 – EASTERN VISAYAS Samar and Leyte Islands. Misamis Oriental and part of Agusan del Sur. Albay. Capiz and Iloilo. Aurora Water Resources Region No. and the island of Panay which consist of the provinces of Aklan. Negros Oriental Predominant Cliamate : Type III Water Resources Region No. Predominant Climate : Type III and Type IV Water Resources Region No. Siquijor. 7 – CENTRAL VISAYAS Cebu. Davao Oriental and Surigao del Sur and South Cotabato provinces. Isabela. 1 – ILOCOS Ilocos Norte. Romblon. Predominant Climate : Type II and Type III and Type IV inslands Quezon. Predominant Climate : Type I Water Resources Region No. 6 – WESTERN VISAYAS Negros Occidental. Predominant Climate : Type I Water Resources Region No. Bataan and portions of Benguet and Province. Province. La Union and part of Mt. Ifugao and Predominant Climate : Type III Water Resources Region No. Sultan Kudarat and Predominant Climate : Type III and Type IV South Cotabato. and Palawan. Kalinga-Apayao. Abra. Predominant Climate : Type I Water Resources Region No. 2 – CAGAYAN VALLEY Cagayan. 24 . Predominant Climate : Type II and Type IV Water Resources Region No. 4 – SOUTHERN TAGALOG Rizal. Maguindanao. Laguna. ZamabaleS. 12 – SOUTHERN MINDANAO Lanao del Norte. Antique. Quezon and Metropolitan Manila in Luzon. Pangasinan. 25 . Mindoro. and Palawan are covered in Type I. CROP Rice: Lowland Palagad Upand Corn: Dry season Rainy season Peanut: Dry season Rainy season Beans: Batao Bountiful Bean Cowpea Cadios Mungo Patani Seguidillas Sitao Soybean Vegetables: Leafy: Cabbage Cauliflower Celery Lettuce Mustard Pechay Fruit: Ampalaya Cucumber Eggplant PERIOD June October January April Ocrober May November May May May October May October May July November May October May May November May September December February June January June January June June June December June November June September February June January June June February June CROP Muskmelon Okra Patola Squash Tomato Upo Watermelon Root: Camote(Sweet Potato) Gabi Ginger Raddish Sinkamas Tugue Ubi Cassava Others: Garlic Onion Sweet Pepper Condol Chayote October October October August August October May October May September May December February February January January December July January June December June Spinach Sweet Peas Carrot Potato(Irish) Talinum Kutchai Arrowroot Tapilan Beets Jute PERIOD November May October May October May October October October November May December May May October October May May May October October October May September May October May October October October October October May October October May May September October May January June December June January June December January January January June February June June December December June June June December December December June December June December June December November December December December June December December June June October January June . Negros.26 27 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. Sorsogon. CROP Rice: Lowland Palagad Upand Corn: Dry season Rainy season Peanut: Dry season Rainy season Beans: Batao Cowpea or Kibal Cadios Bountiful Bean Mungo Patani(climbing) Seguidillas Sitao Soybean Tapilan Vegetables: Leafy: Cabbage Celery Kutchai Lettuce Pechay Cauliflower Mustard PERIOD October May June September March January August Janury August May Febraury January May November Febraury January Febraury January Febraury May January January August December July August November May February September Febraury September June April March July December March May June May April June March March October CROP Fruit: Ampalaya Condol Cucumber Eggplant Melon(ordinary) Muskmelon Okra Patola Squash Tomato Upo Watermelon Root: Camote Carrot Cassava Gabi Ginger Raddish Ubi Others: Irish Potato Endive Onion Garlic Sinkamas Sweet Pepper Chayote Arrowroot Beet Peas Jute Talinum PERIOD June November January March January August March March Whole year March Whole year January August November January August Febraury March April April September June June September April September March March Year Round March .April Year Round Year Round Year Round November .December March .May Year Round February December December November October February August February June January February January June March March March December November March September March September March March March July January January March March January January January - March March July June March March March . the Eastern part of Leyte and a large portion of Eastern Mindanao. Eastern part of Albay. The areas covered are Catanduanes. the Eastern and Northern parts of Camarines Norte and Camarines Sur.Melon September October - February January 28 Endive Snap Bean September October - October December PLANTING CALENDAR PLANTING CALENDAR FOR TYPE 2 CLIMATE NO DRY SEASON with a very PRONOUNCED MAXIMUM RAINFALL from November to January. a great portion of the Eastern part of Quezon. January October . Masbate.January Cucumber May . the Eastern portion of the Mountain Province.January September .November Patola May .January Bountiful Bean May .December Condol June .January October . Southern Quezon.August Mustard May .January Third Crop December .May Soybean May .June October .December Upand April . relatively DRY from November to April and WET during the rest of the year.January November .December Corn: Spinach May .December October .June Third Crop December .June Muskmelon November .January Peas April June November . part of Northern Mindanao. Nueva Vizcaya.January Beans: Eggplant May . Central and Southern Cebu.June November .June Seguidillas May .December October .June October .July Mungo December .June October .January Upo April .December Rainy season April .June Batao May .December Sweet Pepper May .July Cauliflower October .January November .January Root: Vegetables: Sweet Potato April .January October .July Tapilan May .Spinach January - March November - December 29 PLANTING CALENDAR PLANTING CALENDAR FOR TYPE 3 CLIMATE Seasons are not pronounced.October Squash May . Romblon.June Pechay May .July Kadios May . and most of Eastern Palawan.June October .June October .June Tomato October .June October .June Peanut: November .June Melon(ordinary) May .June November .June Rainy season April .January Cowpea or Kibal May .December Sitao May .December October .June November .February Fruit: Ampalaya May . CROP PERIOD CROP PERIOD Rice: Lowland June .January Cabbage April .December Dry season September October Chayote May .June Dry season October . This type of climate covers the Western part of Cagayan(Luzon). Eastern Negros.December Okra May . the Bondoc Peninsula.January October .December Gabi May .December (climbing) November .December October December . Northeast Panay.July Palagad November .June Patani May .January November . Isabela.June Carrot October .June November .June Leafy: November .December Watermelon October . Celery Lettuce May October April October - July December May December Garlic Ginger Irish Potato October October November October - December December December December . . The areas covered by Type 4 climate are Batanes Province.July Cowpea or Kibal May .June Sweet Pepper May .September Root: October .September Kutchai June .February .June October .November Chayote May .June Cucumber June .January Sitao May .June September .January Rainy season April .January Tapilan May .December Eggplant June .January September . Eastern.June December .June Cauliflower April .November September .December Melon November .July January .July Upand April .February Fruit: Ampalaya May .January Mungo May .December October .January Patola May .January Peas June . Northeastern Luzon. Marinduque.February Palagad November .December October .January October . and most of Central.January Vegetables: Watermelon April .June December .June November . Eastern Mindoro.January Kadios May .May Third Crop November .October January .May Leafy: November . Western Leyte.February November .June Celery June .June October .July Bountiful Bean May .June Seguidillas May .June Squash May .June Peanut: September .June January .June Rainy season May .November November .January Camote May .December Batao May .January October .January Carrot May . Western Camarines Norte and Camarines Sur.June November .January Soybean May . Northern Negros.July September .January Corn: Pechay May .June Tomato May .July November .July Lettuce May .Febraury Gabi June .June Beans: October .July Dry season September .June November .February May .January January . CROP PERIOD CROP PERIOD Rice: Lowland May .January September . and Southern Mindanao.January Mustard June .June November .June Spinach April .July Muskmelon November .December Third Crop November . Albay.January Cabbage June .October Patani May .January November .July November .PLANTING CALENDAR PLANTING CALENDAR FOR TYPE 4 CLIMATE RAINFALL more or less evenly distributed throughout the year.July Upo May .June Okra June .January Dry season September .June August . 1.4 2.2 2.5.6.5.1.TABLE OF CONTENTS Section 1.5 2.1.6 2.1.2 GENERAL DAM Determination of Dam Height Dead or Inactive Storage Active Storage Flood Surcharge Freeboard Outline of Dam Height Computation Dam Crest Width Selection of Type of Earth Dam Homogeneous/ Modified Homogeneous Type Zoned Embankment Type Embankment Slopes Seepage Through Earth Embankment Seepage Line Position of Seepage Line Quantity of Seepage Filter Design Embankment Slope Protection Upstream Slope Downstream Slope Title Page 1 1 1 1 3 3 6 7 7 7 7 9 11 13 13 13 13 21 22 22 23 .1 2.2 2.5.1 2.3 2.3.2 2.3 2.0 2.1.1 2.3 2.4 2.5 2.0 2.1 2.6.5.1 2.3.2 2.4 2. 3.1 4.2 5.3.3 4.3 3.3 5.3.3.3.3 5.1 3.3.1 5.4 5.3.3.3.3 3.1 4.0 3.4 Appendix I Title SPILLWAY General Spillway Type and Alignment Spillway Hydraulics Control Section Discharge Channel Terminal Section Structural Requirements OUTLET WORKS General Specific Type and Physical Arrangement Outlet Works Hydraulics Section of Design Discharge Head Combination Sizing of Discharge Pipe Sizing of Impact Type Dissipator Structural Design Considerations IRRIGATION WORKS General Canal Layout and Profile Canal Hydraulics Slide Slopes Permissible Velocity Applicable Formula for Sizing of Canal Freeboard Design of Canal Structures General Design Criteria for Canal Structures Page 24 24 24 24 25 25 31 40 43 43 43 44 44 44 48 48 51 51 51 51 51 52 52 53 53 55 .2 3.0 5.2 4.2 4.4 4.1 5.0 4.Section 3.4 5.3.2 3.2 5.1 3.3 4. 1 2 3 4 5 6 7 8 9 Title Outline of Dam Height and Dam Crest Embankment Slopes for Homogeneous Dams Embankment Slopes for Zoned Dams Permissible Velocities for Non-Cohesive Soils Permissible Velocities for Grassed Channel Outline of USBR Basin Computations Format Cantilever Retaining Wall Parameters Discharge Pipe Computations Format Impact Type Stilling Basin Computations Format Page 8 14 15 27 28 46 41 46 50 .LIST OF TABLES Table No. 3 Elements of Seepage Line Diagrams for Determining ∆a and a Flow Profile Along Spillway Unsubmerged Deflector Bucket Type IV USBR Basin Type III USBR Basin Type II USBR Basin Hydraulic Jump Nomograph (Stilling basin Depth Vs Hydraulic Head for Various Channel Losses) Typical Chute and Stilling Basin Section Typical Outlet Works System Impact Type Energy Dissipator Types of Irrigation Canal Layout Page 2 4 5 10 12 16 17 18 19 20 30 32 33 34 35 39 42 45 49 54 . 1 2 3 4 5 6 7 8 9a 9b 10 11 12 13 14 15 16 17 18 19 Title Reservoir Storage Allocations Reservoir Operation Studies Format and Flow Chart Flood Routing Format and Flow Chart Modified Homogeneous Dam Sections Size of Impervious Core of Zoned Dam Slope Stability Chart No. 2 Slope Stability Chart No.LIST OF FIGURES Figure No. 1 Slope Stability Chart No. ENGINNERING DESIGN 1.0 DAM 2. Included in this section are the procedures. the height of the dam is determined on the basis of the following vertical space requirements in the reservoir.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. 1 . Flood Surcharge d. The dam embankment volumes.0 GENERAL For the Water Impounding Component of the Rainfed Project. it is assumed that dam location. Dead or Inactive Storage Space b. etc. a. 2. Freeboard e. Also included in the later part of this section are the procedures. are relatively small and are available at or in the vicinity of the project site. the earth embankment dam type (homogeneous or zoned type) is considered to be more cost effective over concrete or other types of dam. In the procedures and assumptions that follow. This time magnitude is an agency policy decision. These materials are soil and rock in their many varied forms. 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. Settlement Space allocations of each of the above items are illustrated in Figure 1. Active Storage Space c. consisting of natural earth materials. have already been undertaken..1 Determination of dam Height In general. necessary site investigations as well as prerequisites studies on geology. 2. criteria and assumptions used in the design of a small earth dam and its appurtenances.1. hydrology. 2 . 3 . Flood surcharge height is estimated by flood routing. d.3 Flood Surcharge Flood surcharge space is allocated for the design flood. Reservoir operation study basically “water accounting”. 2.1. Reservoir capacity-elevation relationship. It is dependent on three factors namely.1. c. This volume shall be allocated in the dead storage space as shown in Figure 1. sediment volume shall be computed on the basis of 25 years of accumulation in the reservoir. Among the data and assumptions needed to undertake the reservoir operation study are the following: a. Items a. Maximum surcharge height is the difference between maximum and normal water surface. Shown in Figure 2 are the typical format and detailed flow chart for reservoir operation studies. Magnitude and shape of the inflow hydrograph. e. This space is determined from reservoir operation studies. c. 2. b. No clear-cut formula is involved but the basic principle is to optimize reservoir to meet water requirement. Spillway size opening. b and c are obtained from the results of Hydrologic Studies. Item d is derived from a reservoir topographic map. Reservoir elevation at the end of the operation must be equal to the starting elevation.Unless amended later.2 Active Storage The active storage is allocated primarily for irrigation purposes. Reservoir inflow Reservoir evaporation loss Water requirements Reservoir area-capacity-elevation curves. The study involves trial runs for different hectareage of service area until maximum area is attained with minimum reservoir spill or shortage. a. b. 4 5 . There are a number of methods for flood routing but the basic formula is: I=O+S Where.704 metric H = surcharge height L = spillway width 2. In this all other methods of flood routing. water surface in the reservoir is at normal level at the start of the flood. km V = wind velocity. Moreover. Shown in Figure 3 are format and detailed flowchart for such method. m F = reservoir effective fetch. Spillway rating curve or equation given by the following formula for a broadcrested weir: Q = CLH3/2 Where: -----------------------------------------.4 Freeboard Freeboard space is provided against wave splash along the upstream face of the dam. 1. km/hr Fb2 = freeboard due to embankment settlement.4 Fb = Fb1 + Fb2 ------------------------------------------------------------------5 Where: F b1= freeboard due to wave run-up. It is estimated by the following formula: For vertical wall Fb1 = --------------------3 Fb2 = 2% to 5 % of dam height ------------------------------------------. m Fb = total freeboard.2 Q = discharge over the spillway C = weir coefficient. Hydrograph of inflow design flood. it is assumed that all outlets are fully closed and all discharges are allowed to pass only over the spillway.1. ----------------------------------------. which may coincide with occurrence of the design flood as well as embankment settlement.1 I = inflow volume O = outflow volume S = change in storage A simple and expedient method of flood routing is by arithmetic trial and error. m 6 . Reservoir capacity-elevation curve. The data required to undertake flood routing computations are the following: a. c. b.