PROBLEMS AND OPPORTUNITIES OF LOW-PRESSURE DRIP IRRIGATION WITHOUT
PUMPS
Dr. Eng. Dimitar K. Georgiev1
Drip irrigation is a comparatively new irrigation method applied wider lately due to
water shortage, intensive and competitive farming. The basic advantages of the said
irrigation method are manifested in rather high yields, water savings, high coefficient
of its utilization and high output. In the same time should be considered also the
comparatively high energy consumption compared to the most frequently applied
and traditional water application method - surface (gravity) irrigation where power
consumption or the size of water head respectively is insignificant.
An issue arises - is it possible the dripping irrigation method to be brought closer by
energy consumption to gravity irrigation where pumps except lifting ones are
practically not used. It should be noted that treatment of that problem involves
preliminary disregarding the part of energy in dripping irrigation corresponding to
reduction of water application rate resulted by reduction of the physical evaporation
from the soil. In pursuit of this purpose and on the other hand bearing in mind the
standpoint beyond doubt that an engineering decision aimed at certain effect is so
much rational and technically perfect as the energy consumption is smaller then the
main objective of this report will be to reveal the problems and possibilities for
gaining the planned objective without altering the basic principles of dripping
irrigation. Closer scrutiny of the dripping installation shall reveal that the dripper as
immediate supplier of water to the soil is the main cause to use comparatively high
operating head (energy) in irrigation cells. At present series of manufacturers all over
the world are offering drippers with operating pressure ranging most often from 8 to
12 m with average dripping rate of 4 l/hr. Or expressed in technical terms this will
mean that these irrigation drops could be obtained by raising the piezometric water
level in the irrigation hoses upstream the inlet of each nozzle to height 8 - 12 meters
and that pressure should reach zero value at the end of the nozzle. The basic
objective of that scheme is to draw the hydraulic parameter “flow rate (q) - pressure
(H)” of the nozzles as near as possible to the axis of pressure H in mode that is close
to the turbulent one and than to gain greater length of irrigation laterals (hoses).
The experimental analyses carried out by the author as well as hydraulic analyses are
showing that quite low pressure, close to the zero, shall be required to create flow
rate in the form of drops, observing some drop-forming rules.
Bearing in mind the aforesaid and knowing well the hydraulics and the other
possibilities to gain uniform distribution of flow rate the author has developed on
modular principle, constructed and tested low-pressure drippers with long run of
water and variable length of drop-forming canal along the laterals. The operating
pressure ranges from 0.5 to 1.5 m eliminating thus in most of the cases the need of
pumps. The desired uniformity of flow rate distribution is gained and at thee same
time possibility is created for comparatively much larger cross section of the
1
Bulgaria, Sofia 1734, 1 Hristo Smirnenski St., Chief Assistant, University of Architecture, Civil
Engineering and Geodesy, Hydrotechnical Faculty, Department of Irrigation and Drenage
Engineering
operating canal and the danger of clogging is reduced. Furthermore, it becomes
possible to reduce the requirements to irrigation water quality and consequently to
change the technology and technical decisions for its treatment. The developed
dripper structure is installed parallel on the pipeline (Figure 1) and presents a
labyrinth with 4-mm2 cross section of the canal. Figures 1B and 1C show a provisional
application of dripper in an installation with pulsating drip irrigation using a hydroautomated tank with multi-positional switching over.
Fig. 1: An installation with pulsating low-pressure dripping irrigation
a) long-way dripper with variable length of operating canal; b) scheme of the installation;
c) hydro-automated tank with multi-positional switching over
The relative energy consumption of used nozzles could be considered as main
parameter and basis of comparison for energy consumption of a certain dripping
installation. Figure 2 presents hydraulic parameters of drippers manufactured by
various companies and a ‘section’ of the parameters regarding energy consumption
at a comparatively frequently used flow rate - 2.5 l/h. The relative energy consumed
by one dripper for the various nozzles is calculated with the same volume of water 1 m3, with the time of operation and the flow rates of nozzles being reciprocal
values. The table submitted below shows that energy values obtained in that way are
varying within rather wide range of energy consumption by drippers. Lowest is the
consumption of the TUFFIF GREEN - 8 nozzle of the PLASTO Israeli Company and
highest consumption is of the DLKO2-1 nozzle of the TORO Ag (USA) Company. The
consumption of the second nozzle is seven times as higher as that of the first one. In
the same time should be noted that the lateral potential length of the most energy
consuming nozzle is quite great - depending on the ground slope it may reach 200 300 m but such a length practically is not needed in most cases.
Pr 15
es
su
re
H 12.5
(m
)
GR-16-2 Eurodrip
GR-20-2 Eurodrip
GR-20-4 Eurodrip
GR16-4 Eurodrip
DLK02-1 TORO Ag (USA)
DLK04-1 TORO Ag (USA)
AGRODRiP
TUFFTIF BLACK-2, Plastro
TUFFTIF BLACK-4, Plastro
TUFFTIF GREEN-8, Plastro
Hydrodrip II, 2, 3, Plastro
IHM-KP-4, 6 (BG)
Series14
10
7.5
5
2.5
0
0
1
2
3
4
5
6
7
8
9
Flow rate q (l/h)
Fig. 2. Hydraulic parameter q - H of drippers
Excluding the varying prices of these installations per decare offered by the different
companies the submitted results are indicative and are to be taken into consideration
by future and present landlords and farmers. In addition should be born in mind that
such systems work for a comparatively long period of time - 15 to 20 years, and
sometimes they operate throughout the year (when two or more crops are
cultivated). In regard to the potential comparatively great length of laterals in more
energy consuming drippers should be noted that for the most part it is not used in
and the actual length us rather smaller and dictated by some agronomic and farm
management considerations - roads, canals, boundaries, size of crop rotation plots,
etc.
Energy consumption in KWh x 10-3 by one dripper for
1m3 delivered water with flow rate 2,5 l/h
№
Dripper
1
GR–16-2 Eurodrip
2
GR 20–2 Eurodrip
3
GR 20–4 Eurodrip
4
GR 16–4 Eurodrip
5
DLK02–1 TORO
Ag (USA)
Energy
consumption
37.39
29.32
12.73
11.48
39.08
№
Dripper
7
AGRODRIP
8
9
10
11
TUFFTIF BLACK2, Plastro
TUFFTIF BLACK–
4, Plastro
TUFFTIF GREEN–
8, Plastro
Hydrodrip II, 2,
3, Plastro
Energy
consumption
23.80
34.00
14.42
5.52
30.6
6
DLK04–1 TORO
Ag (USA)
17.00
12
IHM–KP–4, 6
(BG)
11.70
Treatment of irrigation water is another problem occurring when consumption of
pump energy is eliminated (minimized). Pressure filters are applied traditionally sand-gravel and gauze (disc) - where hydraulic (energy) losses are ranging most
frequently from 4 up to 10 m and upstream operating head not lower than 20-25 m
is required. There are two methods to solve that problem:

Increasing the cross section of dripper’s operating canal using nozzles with
varying (modulus) hydraulic parameters along the length of irrigation laterals;

Using pressure-free (or low-pressure) treatment plant - open type. Small
compensating basins or gravity settling basins built up for this purpose especially
could be used. Gauze filters could be placed on their outlets. Since pressure
upstream these filters is rather low the required flow rate could be obtained
increasing their operating area. A system of coarser trash-racks could be installed
upstream the gauze filters. In such a case cleaning these trash-racks shall
impose further problem with a view to prevent eventual back watering and
overflowing of water.
Siphon water intakes with gauze filters built in them could also be used where the
water source is an open canal or tank.
Another opportunity to bring the operating pressure in irrigation laterals to the
minimum and consequent elimination of the necessity to use pumps is to reduce the
flow rate in drippers at the expense of increased time of water application for 24hours (values are reciprocal) - almost continuous irrigation of 18 to 20 h. The
problem arising is whether that minimum dripping flow rate will be sufficient to gain
the required minimum sizes of moistening contours in depth of soil and in the same
time to compensate the evapotranspiration of plants.
Not in the last place should be noted that gaining coefficient of irregular distribution
of irrigation water lower than 10% is not always justifiable from economic point of
view. It is required and proved for conditions only with lasting lack of rainfalls and
where the water application system is the only water source and the soil possesses
low water retaining capacity. In the conditions in Republic of Bulgaria and the
greater part of the European region that coefficient could have higher values since
any heavier rainfall would compensate the effect of irregular water distribution on
yields. This allows application of drippers with lower energy consumption as shown
in the above table.
In conclusion could be noted that a balanced engineering decision providing for
minimum operating head of 0.5 to 1.5 m without usage of pumps and energy in
irrigation laterals could be applied for dripping irrigation of small farm plots where
open water sources are available with certain command position in relation to the
irrigated area. Unfortunately farmers in most cases, under the growing advertising
activity of companies manufacturing dripping irrigation systems and accessories, are
buying complete sets of systems - pumps, filter, irrigation laterals - with practically
unusable potential length - 300 to 400 meters. This raises the cost of the installation
per decare and energy consumption especially if private yards and plots are to be
irrigated.
There also are other possibilities and approaches to achieve that purpose depending
on the flexibility of skill of designers and the available situation.