FISHPOND ENGINEERING 1. INTRODUCTION Fishpond Engineering is the science of planning, designing and constructing ponds including water control structures. Although not entirely new in the Fish Farm industry, it has gained international acceptance and plays an important role for the efficiency of the farm management as well as in attaining higher farm production. Fishpond Engineering takes into consideration most especially the physical structures and economy of construction based on the proper engineering procedure and application. . SITE SELECTION AND EVALUATION OF EXISTING AREAS 2. 1 Water Supply Water supply is the first and most important factor to consider in the suitability of a fishpond site. Usually, water supply comes from a river, a creek or from the sea. It must meet the quality and quantity requirement of the pond system throughout the year. Water quality is affected by the physical, the chemical, and the biological parameters.
Such parameters are affected by the 1) by-products and wastes resulting from urbanization, 2) agricultural pollutants such as pesticides and fertilizers, 3) industrial wastes from pulp mills, sugar, oil refineries, and textile plants, 4) radio-active wastes, 5) oil pollution arising navigational activities, uncontrolled spillage, and oil exploration. Some of these parameters are discussed in detail under fishpond management. Poor quality water sometimes causes the fouling of gates, screens or metal pipes. This happens when heavy dredging is being conducted in an area.
Heavy dredging increases turbidity and causes the release of organic substances embedded in the soil. Once these organic substances are released, they use up oxygen causing high biological oxygen demand (BOD). Higher BOD causes oxygen depletion which in turn makes the water foul. Similar conditions also occur during floods. Water supply in tide-fed farms must be adequate especially during some months of the year when the height of high water is at minimum. This problem can be solved by proper gate design and by the use of pumps.
The rate of volume flow of nearby tidal stream needs also to be considered; measurement is made during the dry stream flow and during floods. The data obtained give the developer the minimum and maximum rates of discharge. These are important requirements in fish farm design. For details, refer to Annex I. 2. 2 Tidal Characteristic and Ground Elevation The suitability of a tide-fed area for a “bangus” fishpond project depends on the relationship between the tidal characteristic of the area and its ground elevation.
The only free source of energy that could be tapped for flooding a brackishwater coastal pond is tidal energy which is available once or twice a day depending on geographical location. Five reference stations in the Philippines exhibit five peculiarly different patterns during some months of the year. Figure 1 shows in a graphical form the relationship of natural ground elevation to tidal characteristic. Tables 1 and 2 show such relationships as they are applicable to the six stations of reference. [pic]
Figure 1 – Suitability of Proposed Fishpond Site Based on Tidal Characteristic and Ground Elevation. |LOCALITY |Elevations in Meters Above Mean Lower Low H20 | | |Mean High Water (MHW) |Mean Sea Level (MSL) |Mean Low Water (MLW) | |Pier 13, South Harbor, Manila |0. 872 |0. 479 |0. 104 | |Pier 2, Cebu City |1. 50 |0. 722 |0. 183 | |Legaspi Port, Legaspi City |1. 329 |0. 744 |0. 165 | |Sta. Ana Port Davao City |1. 405 |0. 753 |0. 101 | |Port of Poro, San Fernando, La Union |- |0. 372 |- | |Jolo Wharf Jolo, Sulu |0. 631 |0. 38 |0. 034 | Table 1. List of Primary Tide Stations and Datum Planes | |Highest |Lowest |Absolute |Normal daily fluctuation |R E M A R K S | | |recorded tide |recorded tide|annual range |low/high(range) (m) | | | |(m) |(m) |(m) | | | |PHILIPPINES |1. 4 |(-)0. 21 |1. 25 |(-)0. 03/0. 61(0. 64) |Tidal fluctuation too | |San Fernando, La | | | | |narrow for proper | |Union | | | | |fishpond management | |Manila City |1. 46 |(-)0. 34 |1. 8 |0. 14/1. 05(0. 1) |Tidal fluctuation | | | | | | |slightly narrow for | | | | | | |proper fishpond | | | | | | |management | |Legaspi City |1. 83 |(-)0. 4 |2. 23 |1. 09/1. 40(1. 9) |Tidal fluctuation | | | | | | |favorable for proper | | | | | | |fishpond management | |Cebu City |1. 98 |(-)0. 4 |2. 38 |(-)0. 03/1. 49(1. 52) |-do- | |Davao City |1. 98 |(-)0. 49 |2. 47 |(-)0. 03/1. 77(1. 80) |-do- | |Jolo, Sulu |1. 19 |(-)0. 12 |1. 31 |(-)0. 03/0. 98(1. 1) |Tidal fluctuation | | | | | | |slightly narrow for | | | | | | |proper fishpond | | | | | | |management | Table 2. Suitability of Six Tidal Stations of Reference for Fish Farms Areas reached only by the high spring tides should be ruled out as it is costly to move large quantities of soil during the process of excavation.
There is that other problem of where to place the excess materials. While these can be solved by constructing high and wide perimeter dikes, putting up more dikes will create narrow compartments resulting in less area intended for fish production. Low areas on the other hand will require higher and more formidable dikes which may mean that earth will have to be moved long distances. The pond bottom should not be so low that drainage will be a problem. The best elevation for a pond bottom therefore, would at least be 0. 2 meter from the datum plane or at an elevation where you can maintain at least 0. meter depth of water inside a pond during ordinary tides. This index should satisfy the requirements of both fish and natural fish food. 2. 2. 1 Tides The attractive forces of both the moon and the sun on the earth surface which changes according to the position of the two planets bring about the occurrence of tides. Tides recur with great regularity and uniformity, although tidal characteristic vary in different areas all over the world. The principal variations are in the frequency of fluctuation and in the time and height of high and low waters.
When the sun, the moon and the earth are in a straight line, greater tidal amplitudes are produced. These are called spring tides. Tides of smaller amplitudes are produced when the sun and the moon form the extremes of a right triangle with the earth at the apex. These are called neap tides. When high and low waters occur twice a day it is called a semi-diurnal tide. When the high and the low occur once a day it is called a diurnal tide. The moon passes through a given meridian at a mean interval of 24 hours and 50 minutes. We call this interval one lunar day.
Observations reveal that the mean interval between two successive high (or low) waters is 12 hours and 25 minutes. Thus, if there is a high water at 11:00 A. M. today, the next high water will take place 12 hours and 25 minutes later, i. e. , 11:25 P. M. and the next will be at 11:50 A. M. of the following day. Each day the time of tide changes an average of 50 minutes. The difference in the sea water level between successive high and low waters is called the range. Generally, the range becomes maximum during the new and full moon and minimum during the first and last quarter of the moon.
The difference in the height between the mean higher high and the mean lower low waters is called the diurnal range. The difference in the tide intervals observed in the morning and afternoon is called diurnal inequality. At Jolo, for instance, the inequality is mainly in the high waters while at Cebu and Manila it is in the low waters as well as in the high waters. The average height of all the lower of low waters is the mean lower low (MLLW), or (0. 00) elevations. This is the datum plane of reference for land elevation of fish farms.
Prediction of tides for several places throughout the Philippines can be obtained from Tide and Current Tables published annually by the Bureau of Coast and Geodetic Survey (BCGS). These tables give the time and height of high and low water. The actual tidal fluctuation on the farm however, deviates to some extent from that obtained from the table. The deviation is corrected by observing the time and height of tidal fluctuation at the river adjacent to the farm, and from this, the ratio of the tidal range can be computed. From the corrected data obtained, bench marks scattered in strategic places can be established.
These bench marks will serve later on as starting point in determining elevations of a particular area. 2. 2. 2 Tide prediction There are six tide stations in the Philippines, namely: San Fernando, Manila, Legaspi, Cebu, Jolo and Davao stations. Reference stations for other places are listed under the “Tidal Differences” and “Constants” of the Tide and Current Tables. The predicted time and height of high and low waters each day for the six tide stations can be read directly from the table. Tide predictions for other places are obtained by applying tidal differences and ratios to the daily predictions.
Tidal differences and ratios are also found in the Tide and Current Tables. Let us take for example, the tidal predictions for Iloilo on 23 Sept. 1979. Looking through the tidal differences and constants of the Tide Tables, you will find that reference station for Iloilo is Cebu. The predicted time and height of tides for Cebu obtained from the tide tables on 23 Sept. 1979 are as follows: |High |Low | |Time |: |Height |Time |: |Height | |0004 |: |1. 3 m |0606 |: |0. 14 m | |1216 | |1. 52 m |1822 | |0. 18 m | (The heights are in meters and reckoned from mean lower low water (MLLW); 0000 is midnight and 1200 is noon). Again, from the table on Tidal Differences and Constants, the corrections on the time and height of high and low waters for Iloilo are as follows: |Time |Height of High Water |Height of Low Water | |+ 0 hr. 05 min. |+ 0. 09 |+ 0. 3 | Thus, the corrected time and heights of high and low waters for Iloilo are: |High |Low | |Time |: |Height |Time |: |Height | |0009 |: |1. 52 m |0611 |: |0. 17 m | |1221 |: |1. 61 m |1827 |: |0. 21 m | 2. 2. 3 Height of tide at any given time
The height of the tide at any given time of the day may be determined graphically by plotting the tide curve. This can be done if one needs to know the height of the tide at a certain time. The procedure is as follows: On a cross-section paper, plot the high (H) and the low (L) water points between which the given time lines (see Fig. 2). Join H and L by a straight line and divide it into four equal parts. Name the points as Q1, M and Q2 with M as the center point. Locate point P1 vertically above Q1 and P2 vertically below Q2 at a distance equal to one tenth of the range of the tide.
Draw a sine curve through points H, P1, M, P2 and L. This curve closely approximates the actual tide curve, and heights for any time may be readily scaled from it. Figure 2 shows the curve on 23 Sept. 1979 for Iloilo. H is 1. 61 m at 12:21 hr and L is 0. 21 m at 18:27 hr. Since the range is 1. 40 m, P1 is located 0. 14 units above Q1 and P2 is located 0. 14 units below Q2. The height of the tide at 14:30 hr is given by point T to be 1. 22 m. [pic] Figure 2. Height of Tide at any Given Time for Iloilo on 23 Sept. 1979. 2. 3 Soil Properties
Most of our fishponds are constructed on tidal lands consisting of alluvial soils which are adjacent to rivers or creeks near the coastal shores and estuaries at or near sea level elevation. If you pick up a handful of soil and examine it closely, you will find that it is made up of mineral and organic particles of varying sizes. The mineral particles are the clay, silt, and sand while the organic particles are plant and animal matter at various stages of decomposition. Soils are assigned with textural classes depending on their relative proportion of sand, silt and clay.
Each textural class exhibits varying colors which are based on their chemical composition, amount of organic matter and the degree of decomposition. U. S. Department of Agriculture Classification System has classified soil as: |GENERAL TERMS | |Common Names |Texture |Basic Soil Textural Class Names | |1. |Sandy Soils |Coarse |Sandy | | | | |Sandy Loam | |2. Loamy Soils |Moderately Coarse |Sandy Loam | | | | |Fine sandy Loam | | | |Medium |Very fine Sandy Loam | | | |Moderately fine |Loam | | | | |Silty Loam | | | | |Silt | |3. |Clayey Soils |Fine |Sandy Clay |Clay Loam | | | | |Silty Clay |Sandy Clay Loam | | | | |Clay |Silty Clay Loam | Many properties of soil, which are related to its texture, determine how well suited it is for fishpond purposes.
A sandy loam, for instance, is more porous than silty loam and the latter will hold more nutrients than the former. Clay or sandy clay may be the best for dike construction but not as good as clay loam or silty clay loam in terms of growing natural food. So, in general, finer textured soils are superior for fishpond purposes because of their good water retention properties. Each soil texture exhibits different workability as soil construction material. Studies conducted show that clayey soil is preferred for diking purposes. Suitability of a soil class as dike material decreases with decreasing percentage of clay present in the mixture (see Table 3). CLASS |RELATIVE CHARACTERISTIC |COMPACTION CHARACTERISTIC |SUITABILITY FOR DIKE | | | | |MATERIAL | | |PERMEABILITY |COMPRESSIBILITY | | | |Clay |impervious |medium |fair to good |excellent | |Sandy clay |impervious |low |good |good | |Loamy |semi-pervious |high |fair to very |fair | | |to | | | | | |impervious |high |poor | | |Silty |semi-pervious to |medium to |good to very |poor | | |impervious |high |poor | | |Sandy |pervious |negligible |good |poor | |Peaty |- |- |- |very poor | Table 3. Relationship of Soil Classes and Suitability for dike material Sediments are a dominant and observable characteristic in lower areas of brackishwater swamplands.
Field observations and laboratory analysis of soil samples taken reveal that the majority have a thick layer of loose organic sediments which make them unsuitable for fishpond development and other infrastructures. Engineering and other technical considerations indicate that areas having this type of soil are rather difficult to develop because it is directly related to future land development problems such as (1) subsidence and related flood hazards, (2) unavailability of stable and indigenous soil materials for diking, and (3) unavailability of land with adequate load bearing capacity for future infrastructures such as buildings for storage and production facilities.
Areas dominated by organic and undecomposed sediments are expected to experience considerable subsidence which eventually result to loss in effective elevation of the land after development as a result of drainage or controlled water table. Since elevation of most tidal lands converted to brackishwater fishponds are generally one meter above MLLW, any future loss of elevation due to subsidence shall predispose the area to severe drainage and flooding problems due to blocking effect of seawater during high tides. Organic and undecomposed sediments are not a good foundation for dikes nor for diking material. Fishpond areas dominated by this type of soil will mean that there is an inadequacy of indigenous soil materials for diking or filling of lower areas.
In the absence of good soil materials, the site under consideration will require importing of soils from the adjoining areas which will make the system of development a very expensive process, or considerable excavation for diking will cause (1) unnecessary exposure of acid organic layers, (2) difficulty in leveling, (3) high cost of dike maintenance and (4) technical problems on seepage losses which will cause difficulty in maintaining water levels in the pond. 2. 3. 1 Field method for identification of soil texture Sand – Soil has granular appearance. It is free-flowing when in a dry state. A handful of air-dry soil when pressed will fall apart when released. It will form a ball which will crumble when lightly touched. It cannot be ribboned between thumb and finger when moist. Sandy Loam – Essentially a granular soil with sufficient silt and clay to make it somewhat coherent. Sand characteristic predominate. It forms a ball which readily falls apart when lightly touched when air-dry.
It forms a ball which bears careful handling without breaking. It cannot be ribboned. Loam – A uniform mixture of sand, silt, and clay. Grading of sand fraction is quite uniform from coarse to fine. It is soft and has somewhat gritty feel, yet is fairly smooth and slightly plastic. When squeezed in hand and pressure is released, it will form a ball which can be handled freely without breaking. It cannot be ribboned between thumb and finger when moist. Silty Loam – It contains a moderate amount of finer grades of sand and only a small amount of clay; over half of the particles are silt. When dry, it may appear quite cloddy; it can be readily broken and pulverized to a powder.
When air-dry, it forms a ball which can be freely handled. When wet, soil runs together and puddles. It will not ribbon but has a broken appearance; it feels smooth and may be slightly plastic. Silt – It contains over 80% of silt particles with very little fine sand and clay. When dry, it may be cloddy; it is readily pulverized to powder with a soft flour-like feel. When air-dry, it forms a ball which can be handled without breaking. When moist, it forms a cast which can freely be handled. When wet, it readily puddles. It has a tendency to ribbon with a broken appearance; it feels smooth. Clay Loam – Fine texture soils break into lumps when dry. It contains more clay than silt loam.
It resembles clay in a dry condition. Identification is made on physical behaviour of moist soil. When air-dry, it forms a ball which can be freely handled without breaking. It can be worked into a dense mass. It forms a thin ribbon which readily breaks. Clay – Fine texture soils break into very hard lumps when dry. It is difficult to pulverize into a soft flour-like powder when dry. Identification is based on cohesive properties of the moist soil. When air-dry, it forms long thin flexible ribbons. It can be worked into a dense compact mass. It has considerable plasticity, and can be moulded. Organic Soil – Identification is based on its high organic content.
Much consists of thoroughly decomposed organic materials with considerable amount of mineral soil finely divided with some fibrous remains. When considerable fibrous material is present, it may be classified as peat. Soil color ranges from brown to black. It has high shrinkage upon drying. 2. 4 Studies of Watershed and Flood Hazard 2. 4. 1 Watershed A watershed is a ridge of high land draining into a river, river system or body of water. It is the region facing or sloping towards the lower lands and is the source of run-off water. The bigger the area of the watershed, the greater the volume of run-off water that will drain to the rivers, creeks, swamps, lakes or ocean. Precipitation from a watershed does not totally drain down as run-off water.
A portion of the total rainfall moving down the watershed’s surface is used by the vegetation and becomes a part of the deep ground water supply or seeps slowly to a stream and to the sea. The factor affecting the run-off may be divided into factors associated with the watershed. Precipitation factors include rainfall duration, intensity and distribution of rainfall in the area. Watershed factors affecting run-off include size and shape of watershed, retention of the watershed, topography and geology of the watershed. The volume of run-off from a watershed may be expressed as the average depth of water that would cover the entire watershed. The depth is usually expressed in centimeters. One day or 24-hours rainfall depth is used for estimating peak discharge rate, thus: Volume of Flood Run-off (Q) [pic]+ S1 Engineering Field Manual For Conservation Practices, 1969, pp 2–5 to 2–6 |where |Q |= |accumulated volume of run-off in centimeters depth over the drainage area | | |P |= |accumulated rainfall in cm depth over the drainage area | | |Ia |= |initial obstruction including surface storage, interception by vegetation and | | | | |infiltration prior to run-off in cm depth over the drainage area | | |s |= |potential maximum retention of water by the soil equivalent in cm depth over the | | | | |drainage area | 2. 4. 2 Flood hazard
Floods are common in the Philippines due to overflowing of rivers triggered by typhoons and the southwest monsoon rain prevailing over the islands during the rainy season. Overflow of the rivers is largely attributable to the bad channel characteristic such as steep slopes as well as meandering at the lower reach of the river. The network of the tidal streams in some delta areas has been rendered ineffective in conveying the flood-water to the sea due to fishpond construction. Flooding is common in this country and is considered the most destructive enemy of the fishpond industry. The floods of 1972 and 1974 greatly affected the fishpond industry in Central Luzon causing damage amounting to millions of pesos.
Because of the floods, fishponds became idle during the time necessary for operators to make repairs and improvements. Floods cannot be controlled, but what is important is to know how a fishpond can be free to some extent from flood hazard. In order to prevent frequent flooding, it is necessary to know the weather conditions in the area where the fishpond project is located. The highest flood occuring in an area can be determined by proper gathering of information. In big rivers, the Ministry of Public Works (MPW) records the height of flood waters during rainy seasons. However, in areas where the MPW has no record, the best way is by gathering information from the people who have stayed in the area for many years.
The size of the creek, river and drainage canal should also be determined to find out whether it can accommodate the run-off water or flood water that drains in the area once the fishpond project is developed. Records of the highest flood in the site, especially during high tide, is very important. It will be the basis in providing allowance for the drainage of flood water coming from the watershed. 2. 5 Climatic Conditions Climate has been described in terms of distribution of rainfall recorded in a locality during the different months of the year. In the Philippines, it is classified into four climatic zones preferably called weather types, namely: |Type I |- |Two pronounced seasons; dry from November to April and wet uring the rest of the year. | |Type II |- |No dry season with very pronounced maximum rainfall from November to January. | |Type III |- |Season not very pronounced; relatively dry from November to April and wet during the | | | |rest of the year. | |Type IV |- |Rainfall more or less evenly distributed throughout the year. | The elements that make up the climate of a region are the same as those that make up the weather, the distinction being one mainly of time. But the elements that concern most fishpond operators are the rainfall, temperature and the prevailing wind direction because they greatly affect fish production directly or indirectly.
Data on rainfall and wind direction are very necessary in planning the layout and design of pond system. Knowing past rainfall records, you can more or less decide whether it will be necessary to include a drainage canal in the layout, and how large it will be when constructed. Knowing past rainfall records will also be necessary in computing the height of the secondary and tertiary dikes. Wind on the other hand, plays a role in fishpond design. Strong wind generates wave actions that destroy sides of the dike. This causes great expense in the construction and maintenance. However, this problem can be minimized with proper planning and design.
For instance, longer pond dimension should be positioned somewhat parallel to the direction of the prevailing wind (see Fig. 3). This will lessen the side length of the dike exposed to wave action. This orientation of pond compartments will also have some advantageous effects in the management aspect. [pic] Figure 3. Layout of Pond Compartments Oriented to the Prevailing Wind Direction Nearly every location is subject to what is called the prevailing wind, or the wind blowing in one direction for a major portion of the year. Monsoons are prevailing winds which are seasonal, blowing from one direction over part of the year and from the opposite direction over the remaining part of the year.
Trade winds, which generally come from the east, prevail during the rest of the year when the monsoons are weak. [pic] Figure 4. Wind Directions Wave action in ponds is caused by wind blowing across the surface. One cannot totally control wave action in ponds although it can be minimized. In typhoon belt areas or in areas where a strong wind blows predominantly, it is better to include wind breakers in planning the layout of ponds. 2. 6 Type and Density of Vegetation Mangrove swamps occur in abundance on tidal zones along the coasts of the Philippines which are being converted into fishponds for fish production, but not all mangrove swamps are suitable for fishpond purposes.
Some are elevated and are not economically feasible for development; others have too low an elevation to develop. The distribution of mangrove species in tropical estuaries depend primarily on the land elevation, soil types, water salinity and current. It has been observed that “api-api” and “pagat-pat” trees (Avicennia) abound in elevated areas while “bakawan” trees (Rhizophora) are mostly found in low areas. It has also been observed that nipa and high tannin trees have a long-lasting low pH effect on newly constructed ponds. Presence of certain shrubs and ferns indicate the elevation and frequency of tide water overrunning the area. Certain aquatic plants such as water lily, eel grass and chara sp. indicate low water salinities.
The type and density of vegetation, the size, wood density and root system of individual trees greatly affect the method of clearing, procedure of farm development and construction cost. Thickly vegetated areas, for instance, will take a long time to clear of stumps. Density of vegetation is classified according to kind, size and quantity per unit area. This is done to determine the cost of land clearing and uprooting of stumps. One method used is by random sampling. The process requires at least five or more samples taken at random, regardless of size, and vegetation is classified according to kind, size and number. Then the findings are tabulated and the average of the samples is determined. However, vegetation of less than 3 cm in diameter is not included.
The total vegetation of the area is determined as follows: [pic] |Station |NIPA |BAKAWAN |API-API |LIPATA |BIRIBID | |(20? 20) | | | | | | | |No|Av|No. | | |. |e. | | | | |Si| | | | |ze| | | |b |= |line GD | | |h |= |height or distance | The total area of the irregular figure is equal to the sum of A1, A2, A3, A4 and A5.
Example: Find the area of an irregular figure shown in Figure 13 using the triangulation method. Solution: [pic] [pic] b. Trapezoidal Rule [pic] Figure 14. Area Determination Using the Trapezoidal Rule If a field is bounded on one side by a straight line and on the other by a curved boundary, the area may be computed by the use of the trapezoidal rule. Along a straight line AB, Fig. 14, perpendicular offsets are drawn and measured at regular intervals. The area is then computed using the following formula: [pic] Where: |ho, hn |= |length of end offsets | |Sh |= |sum of offsets (except end offsets) | |d |= |distance between offsets | Example: In Fig. 4, if the offsets from a straight line AB to the curved boundary DC are 35, 25, 30, 40, and 10, and are at equal distance of 30, what is the included area between the curved boundary and the straight line? Solution: |Area ABCD |= |[pic] | | |= | | | |= |117. 5 ? 30 | | |= |3,525 sq. m. | 3. 2. 3 Laying out right angles and parallel lines a. Laying out right angles. For instance it is required to lay out the center line of dike B (see Fig. 15) perpendicular to that of dike A using a tape.
A simple corollary on the right triangle states that a triangle whose sides are in proportion of 3, 4, and 5 is a right triangle, the longest side being the hypotenuse. In the figure, point C is the intersection of the two dike centerlines. One man holds the zero end of the tape at C and 30 m is measured towards B. Again from C, measure 40 m distance towards A and then from A’ measure a distance of 50 meters towards B’. Line CB’ should intersect line A’ B’. Therefore, line CB is formed perpendicular to line CA. It is always desirable to check the distances to be sure that no mistake has been made. [pic] Figure 15. Laying Out Right Angles b. Laying out parallel lines. In Figure 16, CD is to be run parallel to AB.
From line AB erect perpendicular lines EF and GH in the same manner described in the previous discussion. Measure equal distances of EF and GH from line AB and the line formed through points C’ and D’ is the required parallel. [pic] Figure 16. Laying Out Parallel Lines 3. 3 Topographic Survey 3. 3. 1 Explanation of common terms a. Bench Mark (BM). A bench mark is a point of known elevation of a permanent nature. A bench mark may be established on wooden stakes set near a construction project or by nails driven on trees or stumps of trees. Nails set on trees should be near the ground line where they will remain on the stump if the tree will be cut and removed. Procedure on setting up a bench mark is attached as Annex 4.
It is a good idea to mark the nail with paint and ring the tree above and below also in case a chain saw is used to cut down the tree. The Philippines Bureau of Coast and Geodetic Survey has established bench marks in nearly all cities and at scattered points. They are generally bronze caps securely set on stones or in concrete with elevations referenced to mean sea level (MSL). The purpose of these bench marks is to provide control points for topographic mapping. b. Turning Point (TP). A turning point is a point where the elevation is determined for the purpose of traverse, but which is no longer needed after necessary readings have been taken.
A turning point should be located on a firm object whose elevation will not change during the process of moving the instrument set up. A small stone, fence post, temporary stake driven into the ground is good enough for this purpose. c. Backsight (BS). Backsight is a rod reading taken on a point of known elevation. It is the first reading taken on a bench mark or turning point immediately after the initial or new set-up. d. Foresight (FS). Foresight is a rod reading taken on any point on which an elevation is to be determined. Only one backsight is taken during each set-up; all other rod readings are foresights. e. Height of Instrument (HI). Height of instrument is the elevation of the line of sight above the reference datum plane (MLLW).
It is determined by adding the backsight rod reading to the known elevation of the point on which the backsight was taken. 3. 3. 2 Transit-stadia method of topographic survey The following describes the procedure of determining ground elevations using the engineer’s level with a horizontal circle and stadia rod. A transit may be substituted for the level if care is exercised in leveling the telescope. It is assumed that a bench mark with known elevation has been established. a. Establish your position from a point of known location on the map. In Figure 17, point B is “tied” to a point of known location on the map, such as corner monument C of the area. This is done by sighting the instrument at
C and noting down the azimuth and distance of line BC. The distance of B from C is determined by the stadia-method discussed under area survey. [pic] Figure 17. Establishing Position from a Point of Known Location on the Map b. Take a rod reading on the nearest bench mark (BM), as shown in Figure 18, previously installed for such purpose. This reading is called the backsight (BS), the rod being on a point of known elevation. The height of the instrument (HI) is then found by adding the elevation of the bench mark (Elev. ) and backsight (BS), thus: H. I. = Elev. + B. S. [pic] Figure 18. Transit-stadia Method of Topographic Survey c.
The telescope is sighted to point D, or any other points desired, and take the rod reading. The reading is called the foresight (F. S. ), the rod being on a point of known elevation. Ground elevation of point D is then determined by subtracting the foresight (F. S. ), from the height of the instrument (H. I. ), thus: Elevation = H. I. – F. S. d. Similar procedure is used in determining the ground elevation of several points which are within sight from the instrument at point B. The azimuth and distance of all the points sighted from point B are read and recorded in the sample field notes such as shown in Figure 19. |Sta. |Sta. |B. S. | |Occ. |Obs. | |HAT |= |Highest Astronomical Tide | |GS |= |Elevation of the ground Surface | |MF |= |Maximum Flood level | |FB |= |Allowance for Free Board | |%S |= |Percent Shrinkage and settlement | 1. The design height of a secondary dike is calculated using the following formula: [pic] Where: Hs |= |Height of the secondary dike | |HST |= |Highest Spring Tide | |GS |= |Elevation of the ground Surface | |MR |= |Maximum Rainfall within 24 hours | |FB |= |Allowance for Freeboard | |%S |= |Percent Shrinkage and settlement | 2. The design height of a tertiary dike is calculated using the following formula: [pic] Where: Ht |= |Height of the tertiary dike | |DWL |= |Desired Water Level | |GS |= |Elevation of the ground Surface | |MR |= |Maximum Rainfall within 24 hours | |FB |= |Allowance for Freeboard | |%S |= |Percent Shrinkage and settlement | [pic] Figure 28. Design of Different Dikes 4. 3. 3 Canals. About one to two percent of the total farm area is used in the canal system. The main water supply canal starts from the main gate and usually traverses the central portion of the fishfarm. The canal bed should not be lower than, but rather sloping towards, the floor elevation of the main gate. Generally, the canal bed is given a slope of 1/1500 or one meter difference in elevation for a horizontal distance of 1,500 m. A one meter opening main gate will have a canal bed at least 3. m. wide. This width is enough to supply a 10–15 hectares fishpond system considering that the canal dikes have a ratio of 1:1 slope. Secondary water supply canals are constructed in portions of the farm which cannot be reached by the main canal. It starts from the main canal and traverses the inner portion of the fishpond. It is usually constructed in large fishpond areas and smaller than the main canal. Generally, secondary supply canal has a bed width of 2. 0 m. A tertiary canal is usually constructed to supply water in the nursery and transition ponds. Because of the small size, it is sometimes said to be a part of the nursery pond system.
Some fish culturists modify the tertiary canal as a catching pond. This usually happens when the designed tertiary canal is short, Generally, a tertiary canal has a bed width of 1. 0–1. 5 m. A diversion canal, when necessary, is also constructed to protect the farm from being flooded with run-off water coming from the watershed. It must be strategically located so that run-off will empty on an established disposal area, natural outlets or prepared individual outlets. It should have the capacity to carry at least the peak run-off from the contributing watershed for a 10-year frequency storm. The slope of the diversion canal should be in such a way that water flows towards the drainage area.
A drainage canal is constructed when there is a need to have a separate canal for draining rearing ponds. This is to improve water management in the pond system. It is usually located at the other side of the pond, parallel to the supply canal. A drainage canal is recommended in intensive culture, especially of shrimps. [pic] Figure 29. Design of Different Canals 5. PROJECT COST AND PROGRAMMING The worst error a prospective fishfarm operator can make is to develop an area without project cost estimates and a programme of development. Development money is wasted, and management of the area may be difficult or impossible. Poor planning is the major cause of project failure and even leads to personal bankruptcy.
It is very necessary that preparation of the project cost estimates as well as programme of development be done before any construction is started. It is important to know approximately how much will be spent to finish the whole project. It is better that one knows how and when the project will be constructed and completed. The importance of the project cost estimates and programme of development should not be underestimated. 5. 1 Project Cost EStimates The cost of development can be estimated based on the 1) data gathered in the area, 2) proposed layout plan, and 3) design and specification of the physical structures and other facilities. 5. 1. 1 Pre-development estimates a. For the preparation of Feasibility Study.
Whether the fishpond operator will apply for a loan in the Bank or he will use his own money to finance the development of a fishpond project, a feasibility study of the area is needed. The feasibility study will be his guide in the development and management of the project. All activities such as the development, management and economic aspects are embodied in the feasibility study. It is a specialized work by engineers, aquaculturist and an economist having special knowledge in fishfarming industry. Usually, for the preparation of the feasibility study, the group charges about 2% to 10% of the total estimated cost of development. b. For the Survey of the Area. An area survey includes a topographic survey, and re-location survey.
Whether the area is owned by a private individual or by the government, an area survey by a licensed Geodetic Engineer is very important for the proper location and boundary of the land. It is one of the requirements in the application for a 25-year Fishpond Lease Agreement in the BFAR and also in the application for a loan in the Bank. It must be duly approved by the Bureau of Lands. A topographic survey is necessary in the planning and development of the project. A re-location survey must be conducted to check the validity of the approved plan as well as to avoid conflict in the future. An area and topographic survey done by a Geodetic Engineer will cost about [pic]400. 00 for the first hectare or a fraction thereof and [pic]50. 00 per hectare for the succeeding hectarages.
Re-location survey is cheaper than the area and topographic survey. c. For the Construction of a Temporary Shelter. Experienced fishpond laborers generally do not live in the locality. To be more effective they need to have a place to stay during the construction activities. For the construction of a shelter house made of light material, assume a cost of [pic]300. 00/sq. m. of shelter. This includes materials and labor costs. d. For the Construction of Transport Facilities. Flatboats will be needed in the transport of mudblocks. A banca may be used in going to the site. Cost of construction varies from locality to locality. A flatboat with dimensions of 8′ ? 4′ ? 14″ will cost around [pic]500. 00.
A small banca will cost around [pic]600. 00. e. For Representation and Transportation Expenses. This item is not included in the cost of development of a fishpond project. However, it appears that a big amount is being incurred in representation and transportation expenses before the project is started. Example of expenditures are follow-ups of survey plan of the area, FLA application and bank loan. Other expenses are incurred in canvassing of supplies and materials, survey of manpower requirement and equipment needed in the development of a project. Representation and transportation expenses cover about 10–20 percent of pre-development cost. 5. 1. 2 Development Proper. a.
For the Clearing of the Whole Area. Clearing the area of vegetation can be divided into three categories, namely: 1) cutting and chopping, 2) Falling and burning, and 3) uprooting and removal of stumps and logs. Generally, cutting and chopping costs about [pic]500. 00 per hectare; piling and burning costs about [pic]300. 00 per hectare; and for the uprooting of stumps and removal of logs, costs depend on their size and number per unit area. A hectare pond, for instance, having 200 stumps of size below 15 cm. in diameter will cost about [pic]800. 00. Stumps numbering 50 pieces with diameter over than 15 cm. will cost about [pic]1,000. 00 per hectare.
Cost for the clearing depends upon the prevailing price in the locality. b. For the Construction and Installation of Gates. Cost of construction and installation of a gate can be calculated based on its design and specification proposed in the area. The two kinds of gate commonly constructed in fishponds ( concrete and wood) will be discussed separately. 1. Estimating the cost of construction and installation of a concrete gate: a. Based on the plan of a concrete gate, determine the area and volume of the walls, wings, floor, bridges, toes, aprons and cut walls and compute for the total volume using the following formula: A = L ? W V = A ? t VT = V = V1 + V2 + V3 + … Where: A |= |Area |L |= |Length | |V |= |Volume |W |= |Width | |VT |= |Total volume |t |= |thickness | Determine the number of bags of cement, and the volume of gravel and sand by multiplying the total volume with the factors precomputed for a Class A mixture plus 10% allowance for wastage, thus: |No. of bag cement |= |(VT ? 7. 85) + 10% | |Volume of Gravel |= |(VT ? 0. 88) + 10% | |Volume of Sand |= |(VT ? 0. 44) + 10% |
Class A mixture has a proportion of 1:2:4, that is one part of cement for every two parts of fine aggregate (sand) and four parts of coarse aggregate (gravel). b. Every square meter of a concrete gate uses 6. 0 m. long of reinforcement bar placed at an interval of 0. 25 m. both ways on center. This is equivalent to 1 ? bars at a standard length of 20 feet per bar. The floor and toes use the same size of bar, thus: No. of reinforcement bar = (Af + 4t) ? 1. 5 Where: Af = Area of the floor At = Area of the toes The walls, wings, etc. use two different sizes of reinforcement bar, thus: [pic] Where: Aw = Area of the walls Ax = Area of the wings An = other areas c. Find the total area of a concrete gate by adding all the areas mentioned in (a). Calculate the weight of tie wire no. 6 by multiplying the total area with a standard value per sq. m. of concrete, thus: Weight (kg) = AT ? 0. 3 Kg/sq. m. d. Calculate the volume of boulders needed by multiplying the area of the flooring with the thickness of fill. e. Form lumber can be calculated by multiplying the area of walls, wings and bridges by 2. Plywood can also be used as form. Since lumber measurement is still in feet it should be converted into meter, (see conversion table). Use 2″ ? 3″ wood for form support. f. Bamboo puno could be calculated from the area of the flooring. A square meter of flooring will require more or less 20 puno staked at an interval of 0. 5 m. both ways on center. This, however, depends upon the hardness of the floor foundation. g. Screens and slabs are calculated based on the design of the concrete gate. h. Assorted nails are calculated based on the thickness of the form lumber used. i. Labor cost is 35–40% of total material cost. However, close estimates can be computed by determining the cost of labor for the construction and removal of temporary earth dike, excavation of the foundation, staking of bamboo puno, placing of boulders and gravel, construction of forms, concreting of the gate and others. 2. Estimating the cost of construction and installation of a wooden gate. a.
Based on the plan of a wooden gate, determine the size and number of lumber for the sidings and flooring. Compute for the total board feet using the following formula: [pic] Where: |L |= |Length of lumber in inches | |W |= |Width of lumber in inches | |t |= |thickness of lumber in inches | b. Based on the design and specification of the pillars and braces, compute for the total board feet using again the above formula. c. Determine the size and number of lumber needed for slabs and screen frames and compute the total board feet. d.
Calculate the assorted nails (bronze) based on the lumber used. e. Calculate the coal tar requirement in gallons. f. Calculate the cost of nylon and bamboo screens. g. Calculate the labor cost at 30–40% of the material cost or calculate in detail according to the labor requirement. Calculation includes the construction, painting and installation of the wooden gate and excavation of the floor foundation. c. For the Construction of the Proposed Dikes. Dikes constructed in fishponds vary in sizes. Bigger dikes are, of course, more costly to construct than smaller dikes. In other words, the perimeter or main dike will expend more than the secondary or tertiary dikes.
The cost of construction is calculated based on the volume of soil filled and generally it costs [pic]6. 00 per cubic meter. Labor cost, however, depends on the prevailing price in the locality. Transport distance of soil material to the dike is also considered in calculating the cost of construction. Long transport distance decreases individual output per day and thus will increase construction cost. Working eight hours a day, one skilled worker can finish diking, using one flat boat, based on the following distances: |10 – 100 meter distance |6 – 7 cu. m. /day | |101 – 300 meter distance |5 – 6 cu. m. day | |301 – 500 meter distance |4 – 5 cu. m. /day | d. For the Excavation and Leveling of Ponds. Cost for excavation depends upon the volume of soil left inside the pond after the dikes have been constructed. Considering that some soils have been excavated for diking purposes, only about 60% is left for excavation. Generally, escavation costs about [pic]2. 00 per cu. m. depending upon the prevailing labor cost in the locality. After excavation, leveling of the pond bottoms follows. This involves the cut-and-fill method (excavation and dumping to low portions).
Generally, leveling costs about [pic]2,000. 00 per hectare. e. For the Construction of Facilities. Facilities include the caretaker’s house, working shed, bodega, chilling tanks, etc. For proper estimates there should be a simple plan of the facilities. However, rough estimates can be made based on the floor area of a house to be constructed. For a house made of light materials, assume a cost of [pic]400. 00 per sq. m. floor area; and for concrete structures, assume [pic]1,000. 00 per sq. m. All assumed costs include materials and labor based on 1979 price of materials. f. For the Purchase of Equipment. A fishpond project cannot be operated without equipment.
Examples are fish nets, digging blades, shovels, scoop nets, bolos, etc. These items should be included as part of the total development cost. Such equipment should be listed and calculated. g. Contingencies. There should be a contingency fund for unforeseen expenditures, increase of prices and other materials not included in the above calculations. Assume 10% of the above costs for contingencies. 5. 1. 3 Cost estimate For the purpose of determining the cost of developing a new brackishwater fishfarm project, a typical example of a 50-hectare fishpond project applied to the Bureau of Fisheries and Aquatic Resources for a 25-year Fishpond Lease Agreement is presented below. |I. Pre-Development | | | |1. |For the preparation of feasibility study |[pic]1,000. 00 | | |2. |Re-location of boundaries |2,000. 00 | | |3. |For the construction of temporary shelter for laborers (light materials) |4,000. 00 | | |4. |For the construction of flatboats, 5 units at [pic]500. 00/unit |2,500. 00 | | |5. |For the purchase of small banca, 1 unit at [pic]600. 00 |600. 00 | | |6. For representation and transportation expenses |3,000. 00 | | |Sub-total |[pic]13,100. 00 | |II. |Development Proper | | | |1. |Clearing of the area at [pic]600. 00/ha. (cutting, chopping, burning & removal of logs |[pic]30,000. 00 | | |2. |Construction of dikes (filling, compacting and shaping by manual labor) | | | | |a. |Main dike along bay and river 1,920 linear meters, 6. 0 m base, 2. 0 m crown and 2. 25 m|103,680. 00 | | | | |height or a total of 17,280 cum. at [pic]6. 00/cu. | | | | |b. |Main dike along upland, 840 linear meters, 5. 5 m base, 2. 0 m crown, and 2. 0 m height |37,800. 00 | | | | |or a total of 6,300 cu. m at [pic]6. 00/cu. m | | | | |c. |Main canal dike, 980 linear meters, 5. 0 m base, 2. 0 m crown, and 1. 8 m height, or a |33,957. 00 | | | | |total of 6,174 cu. m. at [pic]5. 50/cu. m | | | | |d. |Secondary dike, 2,540 linear meters, 4. 0 m base, 1. 0 m crown & 1. 5 m height or a |52,387. 50 | | | | |total of 9,525 cu. at [pic]5. 50 per cu. m | | | | |e. |Secondary canal dike, 400 linear meters, 4. 0 m base, 1. 5 m crown and 1. 4 m height, or|8,470. 00 | | | | |a total of 1,540 cu. m at [pic]5. 50 per cu. m | | | | |f. |Tertiary canal dike, 240 linear meters, 3. 5 m base, 1. 5 m crown and 1. 2 m height or a|3,600. 00 | | | | |total of 720 cu. m at [pic]5. 00 per cu. m | | | | |g. |Tertiary dike, 700 linear meters, 3. 0 m base, 1. 0 m crown and 1. m height or a total|7,000. 00 | | | | |of 1,400 cu. m at [pic]5. 00 per cu. m | | | |3. |Construction and installation of gates | | | | |a. |Main double opening concrete gate, 2 units at [pic]20,000/unit including labor cost |40,000. 00 | | | |b. |Construction and installation of 10 units secondary wooden gates at [pic]3,000. 00 per|30,000. 00 | | | | |unit | | | | |c. Construction and installation of 15 units tertiary wooden gates at [pic]1,500/unit |22,500. 00 | | |4. |Excavation and levelling of pond bottoms (cut-and-fill) | | | | |a. |Nursery Pond, 1. 5 ha at [pic]2,000/hectare |3,000. 00 | | | |b. |Transition Pond, 4. 0 ha at [pic]2,000/ha |8,000. 00 | | | |c. |Formation Pond, 8. 0 ha at [pic]2,000/ha |16,000. 00 | | | |d. |Rearing Pond, 32. 0 ha at [pic]2,000/ha |64,000. 00 | | |5. Uprooting and removal of stumps at [pic]600/ha |30,000. 00 | | |6. |For the construction of facilities | | | | |a. |Caretaker’s Hut made of light materials, 2 units at [pic]6,000/unit |12,000. 00 | | | |b. |Bodega, made of light materials for inputs and equipment, 1 unit |5,000. 00 | | | |c. |Chilling tank with shed, made of light materials |3,000. 00 | | |7. |For the purchase of equipment | | | | |a. Nets for harvesting |3,000. 00 | | | |b. |Digging blades and carpentry tools |1,000. 00 | | | |c. |Containers |2,000. 00 | | |8. |Contingencies (10% of cost) |52,350. 05 | | |Sub-total |[pic]562,750. 55 | | |T O T A L |[pic]575,850. 55 | ESTIMATED COST FOR ONE UNIT DOUBLE OPENING MAIN CONCRETE GATE |I. Cost of Materials | | | | |Quantity |Unit Price |Amount | | |1. |Cement |140 bags |[pic]24. 00/bag |[pic]3,360. 00 | | |2. |Sand |10 cu. m. |60. 00/cu. m |600. 00 | | |3. |Gravel |20 cu. m |80. 00/cu. m |1,600. 00 | | |4. |Boulders |8 cu. m |50. 00/cu. m |400. 00 | | |5. Reinforcement Bar | | | |a) ? ? ? 20′ |80 pcs |22. 00/pc |1,760. 00 | | | |b) ? 3/8 ? 20′ |35 pcs |12. 00/pc |420. 00 | | |6. |Plywood form |49 pcs |48. 00/pc |2,352. 00 | | | |(? ? 4′ ? 8″) | | | | | |7. |Lumber (S4S) | | | |a) 2″ ? 2″ ? 12′ |30 pcs |3. 0/bd. ft |360. 00 | | | |b) 2″ ? 3″ ? 12′ |16 pcs |3. 00/bd. ft |288. 00 | | | |c) 1″ ? 2″ ? 12′ |10 pcs |3. 00/bd. ft |60. 00 | | | |d) 1″ ? 12″ ? 12′ |6 pcs |3. 00/bd. ft |216. 00 | | |8. |Assorted Nails |10 kgs |7. 50/kg |75. 00 | | |9. |G. I. Wire #16 |20 kgs |8. 00/kg |160. 00 | | |10. Bamboo Puno |400 pcs |4. 00/pc |1,600. 00 | | |Sub-total |[pic]13,251. 00 | |II. |Labor (40% of material cost) |5,300. 00 | |III. |Contingencies (10% of material cost) |1,325. 00 | | |T O T A L |[pic]19,876. 00 | | |say |[pic]20,000. 00 | ESTIMATED COST FOR ONE UNIT SECONDARY WOODEN GATE |I. Cost of Materials | | | | |Description |Quantity |Unit Price |Amount | | |1. |Ply Board |1″? 10″? 14′ |34 pcs. |[pic]3. 00/bd. ft|[pic]1,190. 00| | | | | | |. | | | | | |1″? 10″? 8′ |3 pcs. |3. 00/bd. ft. |60. 00 | | |2. |Slabs |1″? 12″? 14′ |2 pcs. |3. 00/bd. ft. |84. 00 | | |3. |Pillars and Braces |2″? 3″? 10′ |4 pcs. 3. 00/bd. ft. |60. 00 | | | | |2″? 3″? 8′ |7 pcs. |3. 00/bd. ft. |84. 00 | | | | |2″? 3″? 14′ |2 pcs. |3. 00/bd. ft. |42. 00 | | | | |3″? 4″? 10′ |12 pcs. |3. 00/bd. ft. |360. 00 | | |4. |Screen Frames |2″? 3″? 16′ |2 pcs. |3. 00/bd. ft. |48. 00