Assessment of Irrigation Water Quality Using the Canadian Water Quality Index (CWQI) in the Hilla Main Canal, Iraq

4.1 Chemical analysis

The results of chemical analysis of 11 variables (pH, electrical conductivity (EC), total dissolved solids (TDS), chloride (Cl^-1), sodium (Na⁺), potassium (K⁺), calcium (Ca⁺²), magnesium (Mg⁺²), sulphate (SO4^-2), total hardness (TH), and sodium absorption ratio (SAR)) and the number of 240 tests for all points are shown in Table 3. The average values of five locations for four months are shown in Table 4, while group of water quality based on CWQI shown in Table 5. Table 4 is compared with the specifications mentioned in Table 6.

Accordingly, the pH ranged from 7.1 in February at site 4 to 8.2 in May at site 2, as shown in Table 3. Besides, the average values ranged from 7.38 to 8.06 based on Table 4. In general, it can be considered that concentrations were within specification limits at all sites during the four months.

Table 3. Results of chemical analysis of water for two points on Hilla main canal and three points at head of (HC 19, HC 20 and HC 2L)

Table 4. Average values of five locations of the tested elements during four months

EC values varied from 915-968 µS/cm, where the mean minimum value was 925 µS/cm in February and the highest mean value was 964 µS/cm in May. It is clear that EC varies on the type and concentration of ions in the water, and these values are related to chloride concentrations (Cl), whose average values range from 83 to 88 ppm as in Tables 3 and 4 and increase with increasing temperature as well.

This indicates a growth in the EC values of the main channel and the distributed channels due to the rise in temperatures towards the summer season, as the concentrations increase and the levels of water in the channels decrease. In general, when compared with Table 6, all sites are within the limits due to the absence of a salt source affecting the water.

The TDS concentration ranged between 542 and 587 ppm, and the minimum average value was 551ppm in February, while the highest average value was 583 ppm in May (Tables 3 and 4). Accordingly, the values of TDS and EC are associated with the rate of water releases for each month, according to the system that is followed by the project management of the study area. This water is considered fresh according to the standard specifications, as all values were less than 3000, and it is also considered within the limits in Table 7.

Total hardness (TH) concentrations during this study ranged from 280 ppm in site 2 during February to 512 ppm in site 5 during May. Also, the upper limit of the average values is 497 in the same month (Tables 3 and 4). On the whole, all concentrations of TH in the waters are within the specifications (less than 500) in Table 7, except for the values in locations 1 and 5 during the month of May that were more than 500. In comparison with Table 3, some tests were within the limit (150-300) and therefore classified as difficult, but some of them were more than 300 and were considered very difficult, meaning they are of high difficulty.

The reason is due to the slight increase in calcium and magnesium ions in this month compared to the previous months, although the values of these ions and their rates in Table 3 and Table 4 are within the limits of the specifications.

The irrigation channels that are opened for one month are divided, so the water level decreases and the ions increase in the month of May due to the lack of water imports from the Euphrates River. However, it is considered good for irrigation and agricultural purposes and achieves the goal of the study.

By going to the concentrations of each of potassium (K⁺) and sulphate (SO4^-2) in Table 3 and the average values in Table 4 for all locations and months, it can be said that they were within the limits of the specifications in Table 7, and this reason is due to the absence of a source of heavy water and others.

As for the concentrations of sodium (Na⁺), whose value ranges between 68 and 84 ppm, the average values change between 70 and 82 in Table 3 and Table 4, and in general, when compared in all locations, they were found to be within the limits. As for Na%, all tests fall within the specification limit (20-60) when compared with Table 1, where they are classified between good and permissible.

Also, the sodium absorption rate (SAR) ranged between 8.5 and 10.7, while the average ranged between 8.9 and 10.5, as shown in Table 3 and Table 4. Generally, when compared with Table 7 in all locations, it was found to be less than 15. As for the specification in Table 1, which was used by previous researchers, some tests were less than 10 and therefore classified as low water risks (you should be careful not to use them on sodium-sensitive crops such as avocado), and some of them were more than 10. It is considered a medium-risk area for water, and therefore the soil needs to be washed when used in some months.

4.2 Water quality index (CWQI)

IWQI was developed to measure the overall impact of the hazard groups, including salinity, permeability, basic ion and trace element toxicity, and the various effects on irrigation water quality. This index consists of three variables, each of which has a scale from 0 to 100. A vector is produced in an imagined "objective exceedance" space using the values of the three measures of variance from chosen water quality objectives. As indicated in Table 6, the vector's length is then scaled to fall between 0 and 100 and subtracted from that value to give an index that, for extremely poor water quality, is close to 0 and, for great water quality, is close to 100. Table 3 provides laboratory values and calculations required to apply the recommendations. The following three CWQI factors were used in the current study:

The following equation is used to calculate Factor 1 (F1 (scope)), which represents the proportion of variables to the total number of measured variables that do not reach their objectives:

$F_1=\left(\frac{\text { number of } \text { failed variables }}{\text { total number of variables }}\;\;\;\right) \times 100 \%$          (3)

While Factor 2 (F2 (Frequency)), which expresses the proportion of individual tests that do not meet the objectives (failed tests), is calculated using Eq. (4) to determine how many of the tested or observed values do not meet the objective limits,

$F_2=\left(\frac{\text { number } \text {of} \text { failed tests }}{\text { total number of tests }}\;\;\right) \times 100 \%$          (4)

Factor 3 (F3 (Amplitude)) is the final factor and is calculated in three phases. It shows the degree to which the objectives of the failed test values are not satisfied (amplitude). The term "excursion" is used to describe the frequency with which an individual's concentration exceeds the objective (or falls short of the aim when it falls below the minimum):

excursioni $^{=}\left(\frac{\text { falied test }  \text {value}_\;\;i}{\text { objective}_\;\;j}\;\right)-1$          (5)

excursioni $^{=}\left(\frac{\text {objective}_\;\;j}{\text { falied test value}_\;\;\;\;i}\;\right)-1$         (6)

It is important to note that Eq. (5) should be used when the value of the test must not be greater than the objective, and Eq. (6) should be used when the value of the test must not be less than the target. Both of these situations are discussed further below. After computing the total sum of the individual tests' deviations from the objectives of those tests, one then divides the total number of tests by the sum to obtain the overall amount by which the individual tests are not in conformity with the standard. The normalised sum of excursions (nse), a variable, is considered as follows:

nse $=\frac{\sum_{i=1}^n \text { excursion }_\;\;i}{\text { number } \text {of}  \text { test }}$          (7)

Then, F3:

$F_3=\frac{n s e}{0.01 \ n s e+0.01}$          (8)

Then,

$C W Q I=W Q I=100-\frac{\sqrt{F_1{ }^2+F_2{ }^2+F_3{ }^2}}{1.732}$          (9)

Depending on the laboratory output values of the elements in the Table 3 and using the above equations, the value of the indicator was calculated as shown in the Table 7, where the number of failed variables was (1) in relation to the total number (11) to calculate the factor (F1=9.09). The number of failed checks (2) in relation to the total number (240) to calculate the factor (F2=0.83), as for the value of the deviations of the checks as indicated in the Table 3 from the specification of the Total hardness (TH) was (e1= 0.006 and e2=0.024), as for the value of the sum for them (1.25*10^-4) that is to calculate the value of (F3=0.0125). Through the three values (F1, F2 and F3), Found the Canadian Water Quality Index equal to (94.73), and compared to the specification in the Table 5, where the value is classified between good to excellent. This indicates the water quality for the current study area for irrigation purposes.

It can be established based on the current outcomes that the water samples indicate that all concentrations are within the acceptable and good limits; although they increased slightly in some months, this does not prevent their use for irrigation purposes. The reason is due to the nature of area under consideration, which is characterized by the absence of factories and heavy water streams. Also, the months in which the samples were taken are characterized by a moderate temperature, except that it increased slightly in May compared to the rest of the months in Iraq. In comparison with Karim et al. [19], where the Shatt al-Arab region was used, opposite the current study area, it was found that the concentrations increased due to the presence of the salt source close to it and the nature of the polluted area. Al-Obaidy et al. [7] also does not agree with our current study, as the concentrations increased due to the presence of polluting sources. This necessitates the existence of studies to conserve water for water channels due to its impact on agricultural lands and crops. Furthermore, it was found that all the elements fall within the specifications, as shown in Table 4 which was compared with the specifications mentioned in Table 6, and it was found that all elements fall within the limits except (TH) in the month of May due to the increase in calcium, magnesium, and sulphate ions in this month compared to the previous months, as shown in Table 3.

In general, Table 3 shows the results of the application of this method to the data of the Hilla main canal and three distributary canals (HC 19, HC 20, and HC 2L) for five locations. Accordingly, the Canadian Water Quality Index (CWQI) is 94.73%, which indicates that the quality of water in the Hilla main canal and three distributary canals that are used for irrigation, according to Table 5, is classified as good to excellent.