PHILIPPINE NATIONAL

STANDARD PNS/BAFS/PAES 231:2017

ICS 65.060.35

Groundwater Irrigation – Shallow Tubewell

BUREAU OF AGRICULTURE AND FISHERIES STANDARDS

BPI Compound Visayas Avenue, Diliman, Quezon City 1101 Philippines
Phone (632) 920-6131; (632) 455-2856; (632) 467-9039; Telefax (632) 455-2858
E-mail: bafpsda@yahoo.com.ph
DEPARTMENT OF Website: www.bafps.da.gov.ph
AGRICULTURE
PHILIPPINES
PHILIPPINE NATIONAL STANDARD PNS/BAFS/PAES 231:2017
Groundwater Irrigation – Shallow Tubewell

Foreword

The formulation of this national standard was initiated by the Agricultural

Machinery Testing and Evaluation Center (AMTEC) under the project entitled
“Enhancement of Nutrient and Water Use Efficiency Through Standardization of
Engineering Support Systems for Precision Farming” funded by the Philippine
Council for Agriculture, Aquaculture and Forestry and Natural Resources
Research and Development - Department of Science and Technology (PCAARRD -
DOST).

As provided by the Republic Act 10601 also known as the Agricultural and
Fisheries Mechanization Law (AFMech Law of 2013), the Bureau of Agriculture
and Fisheries Standards (BAFS) is mandated to develop standard specifications
and test procedures for agricultural and fisheries machinery and equipment.
Consistent with its standards development process, BAFS has endorsed this
standard for the approval of the DA Secretary through the Bureau of Agricultural
and Fisheries Engineering (BAFE) and to the Bureau of Philippine Standards
(BPS) for appropriate numbering and inclusion to the Philippine National
Standard (PNS) repository.

This standard has been technically prepared in accordance with BPS Directives
Part 3:2003 – Rules for the Structure and Drafting of International Standards.

The word “shall” is used to indicate mandatory requirements to conform to the

standard.

The word “should” is used to indicate that among several possibilities one is
recommended as particularly suitable without mentioning or excluding others.

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PHILIPPINE NATIONAL STANDARD PNS/BAFS/PAES 231:2017

Groundwater Irrigation – Shallow Tubewell

1 Scope

This standard specifies the procedures in shallow tubewell design, installation

and development within the limits of the capabilities of a suction lift pump.

2 References

The following normative documents contain provisions through which reference

in this text constitute provisions in this National Standard:

PAES 127:2002 Agricultural Machinery – Drilling Rig –

Specifications

PNS/BAFS/PAES 217:2017 Determination of Irrigation Water

Requirements

3 Definition

For the purpose of this standard, the following definitions shall apply:

3.1
aquifer
geologic formation which contains water and transmits it at a rate sufficient to
be economically developed for pumping with a well

3.2
confined aquifer
aquifer where groundwater is confined or overlain by a relatively impermeable
layer

3,3
effective size
particle diameter corresponding to a 10% sieve passing

3.4
pumping test
pumping of water from a fully developed well at a controlled rate and observing,
with respect to time, the drawdown in two or more observation wells, in order to
determine the aquifer hydrologic properties
3.5
shallow tubewell
tube or shaft vertically set into the ground at a depth that is usually less than 15
m for the purpose of bringing groundwater into the soil surface with the use of
suction lift pumps

3.6
unconfined aquifer
aquifer which has water table serving as upper surface of the zone of saturation

3.7
uniformity coefficient
ratio of the particle size at 60% passing to that at 10% passing

3.8
well log
a record of formation stratification of an aquifer showing the depth, thickness,
lithology and other aquifer physical characteristics (Figure A.1)

4 Site Selection

4.1 The site shall ensure adequate yield, which can be reflected through
transmissivity and specific yield, and meet the required irrigation water
requirements.

4.2 The site shall have adequate recharge of the aquifer system such that
there is enough quantity of infiltrating water or is located at a reasonable
distance from surface water bodies.

4.3 The water quality conditions of the aquifer shall meet the minimum
quality requirements for irrigation water imposed by the national implementing
agency.

4.4 The site shall be at an area with low vulnerability to pollution and
seawater intrusion potential.

4.5 The site’s slope, distance from existing boreholes or wells and from
physical discharges of aquifers shall be determined and considered.

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 Table 1. Aquifer properties and their importance in well design, drilling
and development, and in selection of pumping units

AQUIFER PROPERTY IMPORTANCE OR RELEVANCE

Lithological Properties
a. Depth of water bearing
Well design, well depth
formation
b. Aquifer thickness Well design, length of screened or
perforated portion of well
c. Presence or absence of
confining layer (confined, Well design, methods of well drilling and
semi-confined or development
unconfined)
d. Thickness and hardness of Well design, methods of well drilling and
confining layer or layers development
e. Particle size distribution of Well drilling, specifications of well
aquifer materials perforations and gravel envelop in
artificially developed wells
Soil Water Properties
a. Water table or piezometric Feasibility of suction lifting, groundwater
level (annual range of withdrawal amounts before water level goes
fluctuations) down below suction lifting range, well
design, practical limits to STW deep setting,
selection of pumping units
b. Groundwater quality
(salinity, presence of toxic Suitability of water for irrigation
elements)
Hydraulic Properties
a. Hydraulic conductivity or Well design, economic worth of aquifer as
transmissivity water source, well discharged-drawdown
relationships, spacing of wells, maximum
discharge under suction lifting, determining
specifications of STW pumping units
b. Specific yield or storage Established head-storage volume
coefficient relationships and head-pump discharge
relationships, well design, spacing of wells,
specifications of pump sets

Recharge-discharge Properties
a. Probable recharge Estimating safe yields, groundwater
b. Usable recharge conservation and management, planning
c. Groundwater discharge STW irrigation projects
d. Safe yield Shallow aquifer conservation and
management, allocating GW resources
SOURCE: David, W.P. and M.A. Dorado. n.d. Gintong Ani STWIP: Aquifer
Characterization

3
5 Well Characterization

Before proceeding to well design, construction and installation, it is necessary to

determine aquifer characteristics listed above without the expense of a regular
well. In cases where well logs and necessary information are not available,
methods listed in Table 2 may be used.

Table 2. Various Methods Used for Well Characterization and Site

Investigation

Methods Principle
Surface Investigations
Geologic Investigations Preliminary basis in determining potential for
groundwater development; consists of collection,
analysis and hydrodeologic interpretation of
existing topographic maps, aerial photographs,
geologic maps and logs
Remote Sensing Used to determine groundwater conditions from
photographs of the earth taken from aircraft or
satellite at various electromagnetic wavelength;
specific methods include stereoscopic
examination of black-and-white aerial
photographs and infrared imagery
Geophysical Exploration Uses scientific measurement of physical
properties of the earth’s crust for investigation of
mineral deposits or geological structure; findings
are interpreted in terms of rock type and
porosity, water content and water quality
Electrical Resistivity Method Determines actual resistivities from apparent
resistivities computed from current and
potential differences between pairs of electrodes
placed in the ground surface; applications of this
method include the delineation of geothermal
areas, estimation of aquifer permeability,
determination of areas and magnitude of
polluted water
Seismic Refraction Method Uses the introcution of a small shock at the
earth’s surface from the impact of a heavy
instrument or by a small explosive charge, the
time required for the resulting sound to travel to
a known distance is then measured; these
measurements are used to identify the type of
geologic materials in the site and whether these
are favorable or not for test drilling
Subsurface Investigations
Test Drilling Drilling of small-diameter holes to confirm
geologic and groundwater conditions; often used
as observation wells to measure water levels or
for conducting pumping tests

4
  Geologic Log – constructed from sampling
and examination of well cuttings collected
at frequent intervals during drilling
 Drilling Time Log – consists of an accurate
record required to drill each unit depth
which can be interpreted in terms of
formation and depth
Water Level Measurement Determines the depth to groundwater,
groundwater flow directions, changes in water
levels over time and effects of pumping tests;
variation of methods include electric water-level
sounding, air-line method and automatic water
level recording and the use of pressure
transducers
Geophysical Logging Uses sensing devices to determine a physical
parameter which may be interpreted in terms of
formation characteristics, groundwater quantity,
quality, movement and physical structure of the
borehole
Resistivity Logging Uses current and potential electrodes in an
uncased well to measure the resistivities of the
surrounding media wherein the variation of its
traces is related to depth

Spontaneous Potential Uses a recording potentiometer connected to

Logging two similar electrodes to measure the natural
electrical potentials which is then used to
determine permeable zones and to estimate total
dissolved solids in groundwater
Radiation Logging Uses the measurement of fundamental particles
emitted from unstable radioactive isotopes in
cased wells or open holes filled with any fluid;
variation of this method include the use of
natural gamma, gamma-gamma and neutron
logging
Temperature Logging Uses a recording resistance thermometer to
obtain a vertical traverse measurement of
groundwater temperature
Caliper logging Uses caliper tools to measure the average
diameter of a borehole which is used to identify
lithologic properties and stratigraphic
correlation, to locate fractures and other rock
opening, and to correct other logs for hole-
diameter effects

5
6 Types of Shallow Well

6.1 Dug Well – used in unconsolidated formations with large diameters

which permit considerable water storage.

6.1.1 Materials - Wells are constructed through manual excavation using pick
and shovel while the loose materials are hauled to the surface in a container.

6.1.2 Limitations:
 Walls must be lined or braced during and after construction
 Vulnerable to contamination from surface sources

6.2 Bored Well/Augered Well – used in formations with very shallow water
depths

6.2.1 Materials – Wells are constructed using hand-operated or power-driven

earth auger while the loose materials collected in the blades are removed and
then boring is repeated until the desired depth and diameter of the well is
achieved.

6.2.2 Limitation - Should only be used in formations that do not cave;

otherwise, a casing is required to be lowered down the bottom of the hole.

6.3 Driven Well – used in unconsolidated formations with shallow water

tables that contain not too many rocks

6.3.1 Materials - Consists of a series of connected lengths of pipe driven by

repeated impacts to the ground below the water table. Water enters
through the drive point at the lower end of the well with a screened
cylindrical section. Driving can be done with a maul, sledge, drop hammer
or air hammer

6.3.2 Limitations
 Cannot be used on formation with large gravel or rocks that may
damage the drive point
 Joints between the pipes must be carefully made to prevent
breakage and ensure airtight pipe system

6.4 Jetted Well – constructed by the cutting action of a downward-directed

steam of water to excavate the hole and carry the excavated materials out of the
hole.

7 Discharge

7.1.1 The irrigation water requirement shall be determined based on

PNS/BAFS/PAES 217:2017 – Determination of Irrigation Water Requirements.

6
7.1.2 The required pump discharge shall be computed based on the following
formula:

𝐼𝑊𝑅
𝑄𝑟 = × 24
ℎ
where:

Qr is the required pump discharge (lps)

IWR is the irrigation water requirement (lps)
h is the number of hours of operation (h)

7.1.3 The maximum sustained yield that can be extracted from the aquifer shall
be determined using the formula below:

7.1.3.1 Under a steady-state condition in confined aquifers,

2𝜋𝑘𝑏(ℎ2 − ℎ1 )
𝑄𝑠 = 𝑟
𝑙𝑛 𝑟2
1
where:

Qs is the maximum sustained yield (m3/s)

k is the hydraulic conductivity (m/s)
b is the aquifer thickness (m)
T or kb is the transmissivity (m2/s)
h2, h1 is the piezometric water levels at r2 and r1, respectively (m)
r2, r1 is the distance from pumping well to observation wells 2
and 1, resp. (m)

7.1.3.1 For unconfined aquifers,

𝜋𝑘(ℎ2 2 − ℎ1 2 )
𝑄𝑠 = 𝑟
𝑙𝑛 𝑟2
1

7.1.4 Compare the required pump discharge and maximum sustained yield.

7.1.4.1 If Qr is less than Qs, the design pump discharge (Qd) shall be Qr.

7.1.4.2 If Qr is greater than Qs, Qd shall be the adjusted value of Qr. If Qr is

greater than Qs by less than 15%, the value may be adjusted by increasing the
hours of operation or area for non-rice crop. If Qr is greater than Qs by more than
15%, additional tubewell may be needed

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8 Shallow Tubewell Design, Installation and Development in Confined
Aquifer

8.1 Tubewell Design

8.1.1 The tubewell shall be designed such that the discharge is sustainable to
meet the design water requirements, long economic life, low initial cost, low
maintenance and operation costs of the system.

8.1.2 Based on the well log, the water bearing formation with the greater
amount of coarse sand and/or gravel present in the aquifer shall be identified for
tapping.

8.1.3 If more than one water bearing formation is identified, both formations
can be tapped (as shown in Figure A.1.3) for cases where the expected yield from
either formation is not sufficient to meet the projected requirements or where
the characteristic well losses and pumping costs are to be minimized. In such
case, the aquifer in the deeper portion of the well shall be developed first.

8.1.4 The tubewell may be designed such that a smaller diameter borehole is
drilled all the way down to the second aquifer, and the open end of the pipe is
nested on the lower confining layer as shown in Figure A.1.4.

8.1.5 The tubewell may be designed as a well point system such that two wells
are drilled as shown in Figure A.1.5 where each well shall be developed
separately then joined and pumped by a single pump set.

8.2 Pipe Selection

8.2.1 The pipe diameter shall be based on the design discharge. For practical
purposes, Table 3 presents the recommended pipe diameters for various design
discharge and cropping area.

Table 3. Recommended Pipe Diameter Based on Discharge in a Rice-Based

Cropping System

Design Discharge, lps Area, ha Pipe Diameter, mm (in)

3.8 <1 50 or 75 (2 or 3)
7.6 >2 75 or 100 (3 or 4)
>7.6 >2 100(4)
NOTE: The above recommendations are based on the irrigation service area are for crop
water requirement of about 11 mm/day and a 10-hour per day pump operation.
SOURCE: David, et al, Technical Bulletin No. 1 Gintong ani shallow tubewell
irrigation project: design, installation and development of shallow tubewell. DA-
UPLBFI STWIP, 1997

8.2.2 For a well point system, the combined cross-sectional areas of the pipes
shall not be less than that recommended for a single pipe of similar discharge.

8
8.2.3 Pipe materials may be selected as GI or PVC. Table 4 shows the
recommended materials based on the type of well and confining layer.

Table 4. Recommended Pipe Materials

Type of Well Pipe Material

Artificially developed Schedule 20 GI or PVC
Naturally developed with design depth of ≤ 9 m (30 Schedule 20 GI
ft)
Naturally developed with relatively soft confining Schedule 20 GI
layer
Naturally developed with hard confining layer Schedule 40 GI
SOURCE: David, et al, Technical Bulletin No. 1 Gintong ani shallow tubewell
irrigation project: design, installation and development of shallow tubewell. DA-
UPLBFI STWIP, 1997

8.3 Extent of Aquifer Penetration

Table 5. Aquifer Penetration Based on the Type of Well

Type of Well Extent of Aquifer Penetration

Artificially developed 100%
Aquifers of > 4.6 m thickness 85% of the aquifer thickness
Naturally design discharge of < 15 lps < 25%
developed design discharge of > 15 lps 50% - 100%
SOURCE: David, et al, Technical Bulletin No. 1 Gintong ani shallow tubewell
irrigation project: design, installation and development of shallow tubewell. DA-
UPLBFI STWIP, 1997

8.4 Pipe Length

The total pipe length for a single borehole can be computed based on the formula
below and Figure 1.

𝑃𝑖𝑝𝑒 𝑙𝑒𝑛𝑔𝑡ℎ = 𝐸 + 𝐷 + (𝐵 × %𝑝𝑒𝑛𝑒𝑡𝑟𝑎𝑡𝑖𝑜𝑛)

It must be noted that at least 1.2 m (4 ft) shall be added for the nipples needed in
the installation of the pumping unit.

9
 Figure 1. Pipe Length Estimation

8.5 Pipe Perforations

8.5.1 Well pipes can be perforated by cutting with oxyacetylene torch vertical
slots 3 to 6 mm in width and 60 to 90 mm in length around the pipe sections
penetrating the water-bearing formations.

8.5.2 The total area slot openings shall be at least 15% of the surface area of the
pipe.

8.5.3 The pipe bottom shall be open.

8.6 Well Drilling and Pipe Installation

8.6.1 Using the suitable drilling technology, a pilot borehole shall be drilled
down to the design depth. One of the most common drilling technologies is a
drilling rig specified in PAES 127:2002 – Agricultural Machinery – Drilling Rig –
Specifications.

8.6.2 The pilot borehole shall be reamed down to the upper edge of the
confining layer if the confining layer is soft or less than 3m thick, or down to the
lower 2 meters if the confining layer is hard, to ensure air-tight connection
between the pipe and the confining layer.

8.6.3 The pipe can be installed as follows:

8.6.3.1 Lower the pipe into the reamed borehole. If resistance is

encountered, turn the pipe gradually with two pipe wrenches held by one or two
persons riding on them to enhance pipe penetration downward.

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8.6.3.2 Drive by hammering the pipe through the confining layer down to
its designed depth. Avoid turning the pipe during driving as it might destroy the
air-tight connection between the pipe and the confining layer.

8.6.3.3 Careful and controlled water jetting to unclog the pipe may be
done if extreme difficulty is encountered in driving the pipe. Avoid jetting while
the perforated portion of the pipe is in the confining layer. Avoid jetting when
the upper end of the pipe being driven is still high above the ground. The high
static head within the pipe may force water to seep through or bubble up at the
side of the pipe.

8.6.3.4 When the upper end of the screen (slotted portion) has been
driven below the confining layer, jetting or surging may be carried out with
higher velocity water jet.

8.6.3.5 Use good quality couplings (do not use cast couplings). During
driving, couplings may loosen out. Keep couplings tight during driving. However,
avoid turning the lower portion of the pipe when tightening the couplings.

Figure 2. Method of constructing and developing shallow tubewell in

shallow confined aquifer

8.7 Well Development

The well shall be developed to increase its discharge capacity, prevent sand
pumping, attain sustained yield and obtain maximum economic life. Different

11
methods can be used such as pumping, surging, surging with air, backwashing
with air, hydraulic jetting or hydraulic fracturing.

8.7.1 Jetting

8.7.1.1 After installation, jet the well to remove the trapped drilling mud
and the fine aquifer materials. The drilling stem may be fitted with an enlarged
jetting head. Rapid up and down motion of the jetting head will cause water to
surge in and out of the well openings.

8.7.1.2 Start jetting at the bottom of the well until the entire length of the
perforated pipe is cleaned.

8.7.1.3 In aquifers with considerable amounts fine particles or in cases

where considerable amounts of drilling mud are added to the drilling fluid to
stabilize formation during drilling, surging may be done alternately with jetting
to speed up the initial step in well development.

8.7.2 Pumping at low discharges

8.7.2.1 Attach a pump to the tubewell and initially operate at very low and
controlled discharge by attaching to the outlet of the pump set a small hose
(about 1 to 1-1/4 inch in diameter) and control the discharge further by
restricting the opening of the hose.

8.7.2.2 After the initial pumping at low discharge, stop the pumping for
about 10 minutes, after which, resume pumping.

8.7.2.3 Repeat the process until the discharge water clears up. Then
slightly increase the pumping discharge and repeat the process of starting and
stopping the pumping operation.

8.7.2.4 Complete the process until well discharge of clear water is at least
a third of the design discharge.

8.7.3 Pumping at intermediate and higher discharges

8.7.3.1 Develop the well at intermediate discharges and up to a pumping

rate that is 50 percent or more of the design pump discharge. This may require a
bigger pump and/larger diameter pump outlet pipe or hose.

8.7.3.2 Pump at a discharge equal to or slightly higher than the highest

level reached during the second stage of development. Maintain the discharge at
this level until the water clears out.

8.7.3.3 Put the engine throttle to minimum for a few minutes then
increase to attain pump discharge higher than the previous one. Continue
pumping until the water clears out.

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8.7.3.4 Repeat the process until the pumping rate that is 50 percent or
more of the design pump discharge is attained.

9 Shallow Tubewell Design, Installation and Development in

Unconfined Aquifer or with Weak Confining Layer

9.1 Pipe Selection

9.1.1 The pipe shall be designed for full aquifer penetration while the diameter
and material shall be selected based on Table 3 and Table 4.

9.1.2 A gravel pack shall be designed to support the borehole against caving or
formation collapse, to prevent sand pumping after the development and to
minimize characteristic well losses.

9.1.2.1 The effective size (ES) and uniformity coefficient (UC) of the
aquifer materials shall be determined from the mechanical analysis of the aquifer
materials such as sieve-hydrometer and sieve-pipette method of particle size
distribution analysis.

9.1.2.2 The gravel pack specifications shall be determined based on the

following critera:

9.1.2.2.1In aquifers with UC less than 2.0 and ES less than 0.30 mm, a uniformly
grained gravel envelop is needed. The gravel pack should be at least 15 cm thick.

9.1.2.2.2 In aquifers with UC greater than 2.0 but with ES less than 0.30 mm, a
graded gravel pack is desirable. The gravel pack should be at least 15 cm thick.

9.1.2.2.3 In aquifers with ES greater than 0.30 mm, a gravel pack is needed
solely for the purpose of supporting the borehole. A 4 - 7 cm gravel envelop will
suffice.

9.1.2.3 For gravel pack material gradation, the following recommendations of

the US Bureau of Reclamation may be adopted:

9.1.2.3.1 For uniformly grained sand (UC less than 2.0 and ES less than 0.30 mm)

 Multiply the diameter of the aquifer material at 50% passing by 5 and 10

to get two plotting points. Draw a straight line passing through these
points on the same aquifer particle size distribution or gradation curve
(Figure 3). The lines should be approximately parallel to the average
slope of the aquifer gradation curve.

 The optimum gradation of the gravel pack should fall between the two
lines or
limits. A more or less uniformly grained gravel pack can be used.

13
  Well screen or perforation slot size should be less or equal to ½ of 85%
passing of the gravel pack materials. In the example shown on 3, the 85%
passing is about 6 mm and the recommended screen size should be equal
to or less than 3.0 mm.

Figure 3. Gradation Curves for Aquifer Materials and for Uniformly Grained
Gravel Packs

9.1.2.3.2 For graded pack aquifer materials (UC greater than 2.0 and ES less than
0.30 mm)

 Multiply 50% passing size of the aquifer material by 12 and 58; multiply
15% passing size by 12 and 40. Plot the points and limiting curves as
shown on Figure 4.

 No pack material should exceed 15 mm. This will set an upper size limit to
gravel pack materials.

 Gradation curve of pack material (as shown in dashed lines) should fall
between the limits and should approximately be parallel to the aquifer
gradation curve in between 10 and 50 percent passing.

 Screen or perforation slot sizes should be less than ½ of the 85% passing
diameter of the graded gravel pack. In the example on Figure 4 the 85%
passing of the gravel pack materials is about 14 mm and the screen size
should be equal to or less than 7.0 mm.

 The screen opening for aquifers with ES greater that 0.30 mm should be
determined as in the case of graded sands (UC less than 2.0 and ES less
than 0.30 mm).

14
 Figure 4. Gradation curve for aquifer materials and recommended
gradation curve for gravel envelop

9.2 Pipe Perforations

The length of the perforated section of the pipe should then be determined as
follows:

9.2.1 Design for full aquifer penetration.

9.2.2 Estimate the maximum expected drawdown when pumping at the

designed discharge.

9.2.3 Perforate or screen the pipe from the maximum expected drawdown
down to near the end of the pipe. (The bottom of pipe should be plugged).

9.2.4 When the aquifer hydraulic and hydrologic characteristics are not known,
it is not possible to estimate the maximum drawdown. In such cases, the
following rules of thumb may be used:

9.2.4.1 In areas with good aquifer materials (gravel and sand) and where
the water table or piezometric water level is not more than 6 ft from the soil
surface even during the dry season, design for a maximum drawdown of 10 ft.
Perforate the pipe from the estimated water level at maximum drawdown down
to near the end of the pipe.

9.2.4.2 In all other cases, perforate the pipe from 22 ft depth (practical
suction lifting range) all the way down to the end of the pipe.

15
 Figure 5. Recommended lengths of perforated pipe section

9.3 Pipe Installation

7.3.1 Enlarge the borehole down to the designed well depth using a 6-to-8-inch
diameter drill bit. This will create an 8-to-12-inch diameter borehole. In loose,
easy-to-disturb formations, stabilize the sides of the borehole by adding
bentonite (or other suitable clay materials) to the drilling fluid.

9.3.2 Lower the pipe quickly and carefully to avoid disturbing the borehole.

9.3.3 Keep the pipe centered and aligned.

9.4 Gravel Pack Fitting

9.4.1 Pour the gravel in the space/clearance between the pipe and the
borehole, up to near the soil surface to allow for setting or consolidation during
the process of development.

9.4.2 If a thick (20 cm or more) gravel envelope is desired, a 2-to-2.5 inch

diameter gravel pipe may be drilled near the wall of the pipe down to the upper
edge of the well perforations.

9.4.3 Add gravel as needed after development. (Do not grout the well until well
development is complete).

16
 Figure 6. Vertical cross-section of a gravel-packed well

9.5 Well Development

A procedure similar to that for confined aquifer may be used in well

development in
unconfined aquifer. However, the presence of the gravel envelope makes well
development relatively slow. The use of a heavy duty air compressor is,
therefore, desirable.

9.5.1 Use a ¾ to 1-inch diameter air line or pipe.

9.5.2 Initially, place the air pipe inside the well down to the top of the screened
portion of the well.

9.5.3 Release a sustained air pressure of at least 100 psi (120-150 psi is
desirable). This creates a powerful surge within the well forcing the water with
drilled materials up the discharge pipe. When the water coming out of the well
begins to clear, shut down the pressure for a few minutes before turning it on
again. Keep the process of alternately switching the air pressure on and off until
the water coming out of the well clears out of sand.

9.5.4 Lower the air pipe a few feet and repeat the whole process until the air
pipe reaches the bottom of the well.

17
9.5.5 The air pipe may then be repositioned and the air pressure be quickly
turned on and off until the water coming out is practically free of sand.

9.5.6 Add gravel into the space between the pipe and borehole as necessary,
during well development.

10 Selection of Pumping Unit

10.1 Pump Power Determination

10.1.1 The total dynamic head shall be computed as follows:

𝑇𝐷𝐻 = 𝑆𝑊𝐿 + 𝐻𝑓 + 𝐷𝐷 + 𝐻𝑠𝑓

where:

TDH is the total dynamic head, m

SWL is the static water level, m
Hf is the friction losses in the pipes, m (Table 4)
DD is the maximum drawdown when pumping at the design
discharge, m
Hsf is the 0.6 m (2 ft) to account for other head losses

Table 4. Friction losses on GI pipe per 3 m (10 ft) length

PIPE NOMINAL DIAMETER

PIPE FLOW
2 inch 3 inch 4 inch
RATE
(50.8mm) (76.2mm) (101.6mm)
lps gpm ft m ft m ft m
3.15 50 1.00 0.30 0.14 0.04
4.73 75 2.12 0.65 0.29 0.09
6.31 100 3.61 1.10 0.50 0.15
7.89 125 5.47 1.67 0.76 0.23
9.46 150 7.65 2.33 1.06 0.32 0.26 0.08
11.04 175 10.19 3.10 1.42 0.43 0.35 0.11
12.62 200 13.05 3.98 1.82 0.55 0.45 0.14
14.20 225 2.26 0.69 0.56 0.17
15.77 250 2.74 0.84 0.68 0.21
17.35 275 3.27 1.00 0.81 0.25
18.93 300 3.85 1.17 0.95 0.29
20.50 325 4.46 1.36 1.10 0.33
22.08 350 5.11 1.56 1.26 0.38
23.66 375 5.81 1.77 1.43 0.44
25.24 400 6.55 2.00 1.63 0.50
28.39 450 8.15 2.48 2.01 0.61
31.55 500 9.91 3.02 2.44 0.74
SOURCE: David, et al, Technical Bulletin No. 1 Gintong ani shallow tubewell
irrigation project: design, installation and development of shallow tubewell. DA-
UPLBFI STWIP, 1997

18
10.1.2 The brake horsepower shall be computed as follows:

𝑇𝐷𝐻 × 𝑄𝑑
𝐵𝐻𝑃 =
102 × 𝐸𝑝
where:

BHP is the brake horsepower (kW)

TDH is the total dynamic head (m)
Qd is the design pump discharge (lps)
Ep is the pump efficiency (assume 55%)

10.2 The pump shall be selected based on the computed pump design
discharge and total dynamic head and performance characteristics.

10.3 Prime Mover Specifications

The prime mover shall be selected based on the computed brake horsepower. Its
full load continuous duty horsepower shall be greater than the pump brake
horsepower. If such information is not available, Table 5 may be used.

Table 5. Estimated body indicated power rating of various prime movers

Prime Mover Body Indicated Power Rating
Electric motor 1.15 × BHP
Diesel, water-cooled (1.25 − 1.30) × BHP
Diesel, air-cooled (1.30 − 1.35) × BHP
Gasoline, water-cooled (1.35 − 1.40) × BHP
Gasoline, air-cooled (1.40 − 1.50) × BHP
SOURCE: David, et al, Technical Bulletin No. 1 Gintong ani shallow tubewell
irrigation project: design, installation and development of shallow tubewell. DA-
UPLBFI STWIP, 1997

11 Bibliography

David, W.P, M.G. Villano, C.U. Collado, Jr., E.B. Razote and A.L. Ecito 1997.
Technical Bulletin No. 1 Gintong ani shallow tubewell irrigation project: design,
installation and development of shallow tubewell. DA-UPLBFI STWIP

David, W.P. and M.A. Dorado. n.d. Gintong Ani STWIP: Aquifer Characterization

David, W.P. n.d. Chapter IV: Shallow tubewell construction and development

Food and Agriculture Organization. 2014. Irrigation techniques for small-scale

farmers: key practices for drr implementers

Todd, D.K. and L.W. Mays. 2005. Groundwater Hydrology, Third Edition.
Published by John Wiley & Sons, Inc

19
 ANNEX A
(informative)

Well Logging

Procedures described below is a practical method of determining the physical

characteristics of an aquifer adopted from Gintong Ani Shallow Tubewell
Irrigation Project Technical Bulletin No.1. Other recommended methods include
geophysical logging, resistivity logging, spontaneous potential logging, radiation
logging, temperature logging, caliper logging, fluid-conductivity logging and
other subsurface methods.

A.1 Drill a small borehole using a drill bit with a diameter of 2 inches or
smaller. If drilling in unstable, easily disturbed formations, mixing one-to-one
lattice clay (bentonite, potter’s clay or termite mound) with the drilling fluid to
plaster the wall of the borehole during drilling and reduced water jet pressure
and revolutions per minute of drilling stem to reduce the horizontal component
of the drilling mud velocity may be used.

A.2 Drill the borehole (as deep as 45 m or 150 ft if necessary) until a good
aquifer is found. A good confined aquifer is one that is dominated by gravel and
sand, with a thickness of at least 3 m (10 ft).

A.3 Use a pail to collect a sample of a predetermined volume (approximately

14 liters) of the drilled materials at every 1.5 m depth interval and when there is
an indication of a change in geologic formation (change in the rate of penetration
of the drill bit, in hardness of formation or in the particle size distribution of the
drilled materials coming out).

A.4 Carefully pass each sample through a set of screens or sieves with the
following openings: 2, 0.425 and 0.075 mm to retain gravel, coarse sand and fine
sand respectively. However, for practical purposes due to the difficulty in sifting
the particles, 0.6 and 0.15 mm sieves are sometimes used to retain very coarse
sand and fine sand, respectively. Wash with clear water the drilled materials
retained by each screen and place them in plastic bags labeled according to
screen opening and depth. Record the relative amounts of gravel, coarse sand
and fine sand for each sample.

A.5 In some of the samples containing very large amounts of gravel, coarse
and fine sands as well as in samples containing very small amounts of these
materials, collect the samples passing through the set of screens (silt and clay
materials). Allow these to settle for at least an hour. Drain the water and place
the solid particles in plastic bags labeled according to depth. Use these later to
get the estimate of the total volumes of solids coming out of the borehole in
confining layers and good water bearing formations.

A.6 Using the results of procedures A.1 and A.5, characterize or rank each
sampling depth in terms of the relative amounts of gravel, coarse sand, fine sand
and silt/clay (e.g. gravel - highest amount or rank 1, coarse sand – second highest

20
amount or rank 2 and so on). Based on these relative amounts, characterize the
textural composition of each depth (e.g. gravelly sand with fine sand; coarse sand
with gravel; fine sand; hard clay, etc.). It must be noted that a more widely
accepted method of characterizing the textural composition may be used such as
the USDA Textural Soil Classification.

A.7 Prepare the well log as in Figure A.1.

Figure A.1. Well log and alternative well designs

21
 Technical Working Group (TWG) for the Development of Philippine
National Standard for Groundwater Irrigation – Shallow Tubewell

Chair

Engr. Bonifacio S. Labiano

National Irrigation Administration

Members

Engr. Felimar M. Torizo Dr. Teresita S. Sandoval

Board of Agricultural Engineering Bureau of Soils and Water Management
Professional Regulation Commission Department of Agriculture

Dr. Armando N. Espino Jr. Dr. Elmer D. Castillo

Central Luzon State University Philippine Society of Agricultural Engineers

Dr. Roger A. Luyun Jr. Engr. Francia M. Macalintal

University of the Philippines Los Baños Philippine Council for Agriculture and Fisheries
Department of Agriculture

Project Managers

Engr. Darwin C. Aranguren

Engr. Romulo E. Eusebio

Engr. Mary Louise P. Pascual

Engr. Fidelina T. Flores

Engr. Marie Jehosa B. Reyes

Ms. Micah L. Araño

Ms. Caroline D. Lat

Mr. Gerald S. Trinidad

University of the Philippines Los Baños –

Agricultural Machinery Testing and Evaluation Center