Bachmat, Yehuda

Haruvy, Nava

Yaron, Dan

English

Research Papers in Economics

EFFECT OF URBAN DEVELOPMENT ON WATER QUALITY-
ENVIRONMENTAL CONCERNS
Nava Haruvy, Yehuda Bachmat, Sarit Shalhevet, Dan Yaron
Agricultural Research Organization, The Volcani Center, P.O.Box 6, Bet Dagan
50250, Israel. E-mail: navaharu@netvision.net.il
Presented at the 40
th Congress of the European Regional Science Association
European Monetary Union and Regional Policy
Held through 29 August- 1 September 2000 in BarcelonaEFFECT OF URBAN DEVELOPMENT ON WATER QUALITY-
ENVIRONMENTAL CONCERNS
Nava Haruvy, Yehuda Bachmat, Sarit Shalhevet, Dan Yaron
Agricultural Research Organization, The Volcani Center, P.O.Box 6, Bet Dagan 50250, Israel.
E-mail: navaharu@netvision.net.il
ABSTRACT
Urban development increases sewage quantity, which should be treated and discarded. One way of sewage disposal is
treating influents and directing treated effluents to agricultural use. This may help in environmental threat while supplying
irrigation water to agriculture. However, following a long run use, quality of aquifer can be worsened due to some pollutants
remaining in treated effluents. One source is salinity, which is higher in wastewater following domestic use. It may affect soil
structure as well as groundwater quality. This effect can be diminished if combining desalinization and wastewater
treatment processes. We will assess costs and benefits of wastewater treatment and/or reuse by incorporating desalinization
and treatment processes to maintain groundwater quality and prevent environmental aggravation.
Key words: water quality, wastewater, economics, desalinization, urban development
BACKGROUND
Annual water resources in Israel are limited and account to 2,000 MCM (Million Cubic
Meters). With the increase of population, domestic demand for water increases, and
agricultural supply should be based on marginal water sources (Yaron, 1997).
Meanwhile, wastewater sources increase with population growth and should be treated
and discarded. Reuse of treated effluents serves as water source for agriculture while
acting also as an environmental quality agent.
There are many advantages arising from the use of effluents in agriculture including: i.
Treated wastewater will provide for continuity of Israeli agricultural existence under
water scarcity conditions. ii. The supply of effluent increases with population growth.
iii. The cost of treating secondary effluent is relatively low as compared to other water
sources. iv. Reuse of effluent in irrigation is the cheapest option for its disposal in most
cases. V. Secondary effluent contains nutrients, which may save on the use of chemical
fertilizers (Haruvy et. al., 1999).
There are also disadvantages resulting from reusing wastewater in irrigation related to
environmental effects on human health, soil and groundwater (Hadas et. al., 2000;
Haruvy et. al., 2000). Also, costs for individual farmers increase reflecting potentialdamage to crops, adaptation costs of irrigation system and, increased water
requirements due to salinity and evaporation at storage reservoirs. Economic cost -
benefit analysis will assist in focusing on benefits, costs and damages involved with
wastewater reuse (Haruvy, 1997a, 1997b, 1998). Farmers should be motivated by
pricing measures to use water efficiently (Tsur and Dinar, 1997) but prices should
reflect positive as well as negative externalities of irrigation.
COSTS AND DAMAGES
The costs of transition from irrigation with high quality water to effluent can be
classified as financial cost or potential damage to environment, soil, groundwater or
crops.
Financial Cost
Financial cost is measured in terms of supply cost of wastewater including treatment,
storage and conveyance, or adaptation cost of irrigation system. Table 1 presents the
supply cost of wastewater. Capital cost is evaluated according to annual capital return or
sinking funds reflecting only depreciation allowance. We assume that in the case of any
new element in the supply/irrigation system, which must be installed in transition to
effluent, the farmers should receive a full grant to cover the cost. Hence, they should
make an allowance only to depreciation fund and not interest return. Anther financial
cost refers to the adaptation of the irrigation equipment, e.g. filters, chemicals, and the
cost of quality control. They are represented in Table 2 along with their cost estimates.
Table 1: Annual Cost in Transition to Irrigation with Effluent in Terms of Water
Supply System (NIS m
-3) (1$=4 NIS)
Item Capital Return
Cost
Allowance to
Sinking Found
Cost
Recommended to
Farmers
Treatment Cost
Secondary
Treatment
0.65 0.30 0.00
Conveyance Cost
Conveyance to
Storage
0.09 0.05 0.05
Storage 0.28 0.13 0.13
Conveyance to
Fields
0.28 0.12 0.28
Total Conveyance 0.65 0.30 0.46
1) Treatment is up to secondary level. Upgrading up to the tertiary level costs 0.73NIS m
-3.
2) “Representative” Scenario: Wastewater volume: 5 million cubic meter, distance to storage: 5 km; distance to
fields: 5 km.Other additional costs to farmers are presented in Table 2. They include storage cost,
and, additional costs to irrigation system and leaching.
Table 2: Other Additional Costs to Farmers in Transition to Irrigation with
Effluent (NIS m
-3)
Item Annual Cost
Storage Cost
10% losses due to evaporation 0.05
Change of quality n.a.
Follow-up and quality control 0.05
Irrigation system
Filtration chlorinating chemicals 0.10
Accelerated depreciation 0.02
Maintenance 0.01
Leaching irrigation
10% of irrigation water 0.05
Soil salinity tests 0.02
Misc. (elimination of most vegetable
crops, additional labor, etc.)
Total additional cost and damages 0.40
Effect on crop yields
We concentrate on factors as salinity in soil solution and nitrogen in wastewater
affecting crop yields.  Irrigation with saline water including wastewater causes
accumulation of salts in the root zone decreasing crop yields. This damage can be partly
avoided be leaching, computed conventionally as based on “leaching fraction”. This
approach leads to approximate results with respect to leaching effects of rainfall and soil
characteristics. When more accurate estimates are required, arises the need to abandon
the assumption of steady state and to refer to dynamic conditions prevailing in the soil.
We have designed an initial model aiming at estimating variations of soil moisture and
salinity. The model refers to citrus growing in Central Israel. The root zone was divided
into 4 layers consuming water at rates of 0.4, 0.3,0.2 and 0.1, respectively. Initialsalinity levels were 2, 0 and 1 ds/m in irrigation water, rain and soil. Salinity levels were
computed following 5 irrigation and 5 rain periods. Figure 1 presents change of salinity
in soil layers (detailed model will be published).
Figure 1: Salinity levels in soil layers
Yield losses increase with soil salinity in the root zone according to crop sensitivity.
This salinity can be decreased with increased leaching fraction and crop losses should
be compared with additional water cost.
It should be noted that irrigation with secondary effluent including nitrogen (without the
application of the nitrification-denitrification module) is advantageous, due to potential
saving in nitrogen fertilizers. However, this advantage is relevant only with respect to
low-income crops, mainly field-crops. Excessive nitrogen supply in inadequate timing
may cause damages to crops e.g., to yield levels and/or yields quality. Potential losses
of revenue due to excess of nitrogen have been estimated at 2% in cotton, 6% in
avocado, 10% in mango, 11% in citrus Shamouti variety, and 10% in grapefruit, and no
damage in corn for forage or silo.
Salinity levels in soil layers
￿.￿￿￿
￿.￿￿￿
￿.￿￿￿
￿.￿￿￿
￿.￿￿￿
￿￿.￿￿￿
￿￿.￿￿￿
￿￿.￿￿￿
irrigation￿ irrigation￿ irrigation￿ irrigation￿ irrigation￿ rain￿ rain￿ rain￿ rain￿ rain￿
period
s
a
l
i
n
i
t
y
 
d
s layer￿
layer￿
layer￿
layer￿Effect on soil
Soil is affected by salinity expressed as SAR, which is an index representing the ratio
between sodium (Na) and calcium and magnesium (Ca & Mg) in water. The major
immediate hazard of irrigation with high SAR ratio (SAR>6, EC<4 ds/m) is sodifying
the soil surface and deep soil layers. During irrigation cycles, sodium will replace
calcium on the soil clay particles and, destabilize the soil structure. This may, and often
does, reduce soil surface infiltration to water and drainage of the root zone through
lower layers.
The consequences are reduced water uptake into the soil; increased losses of irrigation
and rainwater; increased run off; and, ineffective leaching of accumulates salts in the
soil root zone affecting yields. Damage can be estimated by costs of additional labor
and irrigation water and decreased yields.
Effect on contamination of groundwater
One of the problems involved in irrigation with effluent is the danger of acceleration of
contamination of groundwater mainly by chlorides, nitrogen and heavy metals
(Wallach, 1994).  We designed an approach to the economic evaluation of acceleration
on the concentration of chlorides on groundwater due to irrigation with effluent.
The approach is based on hydrological model predicting the flow of chlorides through
the unsaturated zone of the subsoil, into the groundwater below. Time needed for the
completion of the flow of chlorides inputs through the unsaturated zone, is about 5 years
close to the seashore of Israel. It takes about 20 years in the central part of the Coastal
Plain, and tens up to hundreds of years in the southern-east part of the Coastal Plain.
A threshold for chloride concentration in the water supply for human consumption was
assumed to be 250 mgl. (The current requirement of chlorides is 250 mgl Cl in Israel
and 100 mgl Cl in Europe; it is assumed that in the future, the required threshold in
Israel will be 150 mgl Cl).The model assumes that when the concentration of chlorides in the groundwater reaches
the threshold of 250 mgl Cl or some value somewhat higher than the threshold,
desalination of groundwater should be applied using the reverse osmosis technology.
The point of time when desalination should be applied under conditions of irrigation
with effluent, as compared with the point of time under conditions of irrigation without
effluent, is the basis for the economic evaluation of the damage caused to groundwater
by irrigation with effluent. The timing of introduction of desalination (i.e. the level of
chloride concentration in groundwater) as well as the level of chloride concentration in
the output water of the desalination plant is subject to optimization. The damage to
groundwater by effluent irrigation is computed as increased capitalized costs dew to
water production, wastewater treatment and earlier desalinization.
We will describe salinity according to scenario 1 based on the following assumptions:
Agricultural area 1211 ha with citrus growing, urban area 1052 ha with population of
120,000 inhabitants. Water consumption of agriculture is 9.1 MCM (7,500 CM/ha) and
of town is 12.0 MCM  (100 CM per capita). Initial aquifer salinity is 250 mgl and
domestic threshold is 150 mgl. Wastewater salinity is 350 mgl and rain salinity is 10
mgl. The town uses local aquifer water and agriculture uses treated effluents.
Other scenarios include: scenario 2 in which the town consumes local aquifer water.
Imported aquifer water with salinity level of 176 mgl and national carrier water with
salinity level of 220 mgl. Agriculture uses aquifer surplus as well as the other two water
sources. In scenario 3 the town consumes local aquifer water and national carrier water.Table 3: Quantity and Salinity of various scenarios
Source Scenario1 Scenario2 Scenario3
Quantity Salinity Quantity Salinity Quantity Salinity
Aquifer 488 241 488 241 488 241
Rain (mm) 550   10 550   10 550   10
Wastewater 9.08 350 0.00 350 0.00 350
National
carrier
0.00 220 6.95 220 9.95 220
Imported
aquifer
4.82 250 6.95 176 3.95 150
Figure 2: Salinity change for various water consumption groups
aquifer salinity through time
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￿￿￿
￿￿￿
￿￿￿
￿￿￿
￿￿￿
￿￿￿
￿ ￿ ￿ ￿ ￿ ￿ ￿ ￿ ￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿ ￿￿
year (since steady state )
s
a
l
i
n
i
t
y
 
C
l
 
m
g
l
aquifer salinity
salinity for agricultural use
salinity for urban use
salinity of rain
We computed costs for the three scenarios under the assumption that supply water for
the town are desalinized at threshold level of 250 mgl (Table 4).Table 4: Calculated costs for various scenarios
Current
desalinization
cost
Capitalized
desalinization
cost
Supply
cost to
town
Supply cost
to
agriculture
Total
supply
cost
Total
capitalized
supply cost
Present value
Scenario1 102.40 18.43 489.6 295.1 784.8 273.7
Scenario2 1.66 0.16 471.6 381.1 852.7 310.3
Scenario3 0.73 0.07 517.6 381.1 898.7 327.7
Annual capital return
Scenario1 5.61 1.01   26.82   16.17  42.99   15.00
Scenario2 0.09 0.01   25.84   20.88  46.72   17.00
Scenario3 0.04 0.003   28.35   20.87  49.23   17.95
One can see that in scenario 1 which is based on wastewater irrigation, desalinization
costs are high because of desalinization advancement. Still, due to lower cost of
wastewater, total regional cost of water supply is relatively low. It should be mentioned
that final salinity levels of groundwater after 40 years from steady state are 359, 278 and
289 mgl for scenarios 1, 2 and 3, respectively.
CONCLUSIONS
Urban development increases sewage quantity, which should be treated and discarded.
Agricultural use of treated effluent assists disposing sewage and keeping environmental
quality while supplying irrigation water to agriculture. However, reuse of wastewater
may affect crops, soil and aquifer depending on treatment level and irrigation practices.
Following a long run use, quality of aquifer can be worsened due to some pollutants
remaining in treated effluents for example, salinity, which is higher in wastewater
following domestic use. This effect can be decreased when combining desalinization
and wastewater treatment processes. We assessed costs of wastewater treatment and/or
reuse by incorporating desalinization and treatment processes to maintain groundwater
quality and prevent environmental aggravation.References
Hadas, A., Hadas, A., Sagiv, B., Haruvy, N. (2000). Agricultural practices, soil fertility management modes and
resultant nitrogen leaching rates under semiarid conditions, Agricultural Water Management (in press)
             Haruvy,  N.,  (1997a),  Agricultural  reuse  of  wastewater:  nation-wide  cost  benefit  analysis,  Agriculture,  Ecosystems  &
Environment 66: 113-119
Haruvy, N., (1997b), Wastewater irrigation- economic considerations as affecting decision-making, Journal of Financial
Management and analysis 10 no 1:69-79
Haruvy, N., (1998), Wastewater reuse- regional and economic considerations
Resources, Conservation and Recycling 23: 57-66
Haruvy, N., Offer, R., Hadas, A., Ravina, I. (1999). Wastewater irrigation- economic concerns regarding beneficiary and
hazardous effects of nutrients, Water Resources Management vol. 13 No. 5: 303-314
Haruvy, N., Hadas, A., Ravina, I. Shalhevet, S. (2000). Cost assessment of averting groundwater pollution, Water,
Science & Technology (in press)
Tsur, Y., Dinar, A. (1997). The relative efficiency and implementation costs of alternative methods for pricing irrigation
water, The World Bank Economic Review, vol.11 no. 2:243-262.
Wallach, R. (1994). Groundwater contamination by sewage irrigation:  189-202 in Zoller (ed.): Groundwater
Contamination and Control, Marcel Dekker, Inc.
Yaron, D. (1997). The Israeli water economy: a review, in Decentralization and Coordination of Water Resource
Management, D.D. Parker and Tsur (eds.), Kluwer Academic Publishers: 9-22.

Agricultural practices, soil fertility management modes and resultant nitrogen leaching rates under semiarid conditions, Agricultural Water Management (in press) Haruvy, N.,

Groundwater contamination by sewage irrigation: 189-202

The Israeli water economy: a review,

EFFECT OF URBAN DEVELOPMENT ON WATER QUALITY- ENVIRONMENTAL CONCERNS

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EFFECT OF URBAN DEVELOPMENT ON WATER QUALITY- ENVIRONMENTAL CONCERNS

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