Abstract

Wadi Bandawaya, which is 40 km north of Mosul in Iraq, pierces Mount Dahqan and creates a small valley that is ideal for the construction of a dam for harvesting rainwater. Water quality is evaluated for domestic and agricultural uses using chemical analyses of the main cations (Ca²⁺, Mg²⁺, Na⁺, K⁺), anions (HCO₃^-, SO₄^2-, Cl^-, NO₃^-), as well as measurements of the acidity function (pH), electrical conductivity (Ec), concentration of total dissolved salts (TDS), and total hardness (TH). The valley water is considered to be within the limits permitted for drinking by the World Health Organization. If held inside the water harvesting project of the Bandawaya dam, the water of Bandawaya Valley is freshwater, suitable for drinking and domestic applications, according to the water quality index (WQI). It is also suitable for irrigation of agricultural lands adjacent to the valley in accordance with standards of the percentage of sodium (SSP), the rate of sodium adsorption (Sodium Adsorption Ratio, SAR), the quantity of residual sodium carbonate (Residual Sodium Bicarbonate, RSBC), and the percentage of magnesium (MAR). When there is little rain, the harvested water will be used for irrigation, as well as for supplemental irrigation techniques.

1 Introduction

Particularly in semi-arid and Mediterranean climate regions, the recent climatic changes and water scarcity have become significant challenges. In order to maintain the usage of surface water, particularly in agriculture, rainfall gathering, storage, and preservation are necessary, (Adham et al. 2017). The variations in rainfall and the shortage of surface water in arid and semi-arid areas serve to emphasize the significance of groundwater and springs (Vasanthavigar et al. 2010). Following their descent into the valleys, these springs serve as a source of surface water that eventually forms streams or small rivers. The chemical composition of spring water reflects the caliber of the water that seeped into groundwater through rocks and soil before emerging as springs (Dikeogu et al. 2018). Rain, and occasionally snowmelt, are thus the main sources of groundwater recharge in these areas.

There are a number of variables that affect how rainwater's chemical qualities change, including the chemical watershed basin and the susceptibility of specific mineral phases in reservoir rocks or soils to degrade and dissolve. (Vasanthavigar et al. 2010; Vishnupriya et al. 2015, and Leizou et al. 2017). Wagner (2011) discusses the impact of carbon dioxide gas, dissolved in rainwater, on the dissolution of certain minerals, particularly the carbonate phases. In addition, the effects of several human activities, such as farming and domestic trash (Raju et al. 2011) are also factors to be considered. Groundwater's chemical makeup is the consequence of geochemical reactions that take place when water interacts with the underlying geological components from which it flows (Aghazadeh and Mogaddam 2010). The quality of groundwater, the type of rock it passes through, the type and quantity of soluble minerals, the area where the rocks and water come into contact, (Leizou et al. 2017; Simpi et al. 2011), the medium temperature, flow velocity, topography, and geological structures, are all factors that affect the water quality of streams. (Meuli and Wehrle 2001). Rivers are the most often used source of water, thus any changes in their properties or pollution will have an impact on human existence and the food chain, either directly through water supply or indirectly through agricultural activity (Ahmad et al. 2009).

Geological Setting

In northern Iraq, the Alqosh and Dahqan mountains are situated 20 kilometers south of Dohuk city, and roughly 40 kilometers north of Mosul city, while Jabal Zawa borders Dohuk city on its southern side. These mountains stand in for the respective anticlines of Alqosh, Dahqan, and Dohuk. The Alqosh and Dahqan folds are characterized as wide, low amplitude, low slope, and asymmetrical folds (Fouad 2015). The Dahqan anticline is 11 km long and 2-4 km wide, and the Alqosh anticline is 19 km long and 5-8 km wide, the axis of the two folds are east-west, and they have two plunges (Al-Azzawi et al. 2014) (Figure 1). While the Dohuk anticline (in an east-west orientation) has a length of around 22 km, it is also narrower and higher.

Figure 1 Topographic map of the studied area.

These mountains consist of dolostones from the Pila Spi Formation, (Middle Eocene). The rocks range in color from white to yellowish gray, have thick to huge layers, and include relatively few fossils, aside from cherts and iron oxides.(Sissakian and Al-Jibouri 2014). On both sides of the folds, at the feet of the mountains, rocks from Fat'ha Formation (Middle Miocene) and Injana Formation (Upper Miocene) are exposed. The Fat’ha formation consists of cyclic sediments; each ideal cycle consists of a repetition of carbonate (limestone/dolomite), anhydrite, gypsum, salt rock, and marl. However, the main constituents exhibit lateral and vertical variations, even in a short distance. The Injana Formation consists of a cyclic repetition of claystone, siltstone, and sandstone, and the cycles are coarsening upwards (Jassim and Goff 2006).

The syncline structure, in an east-west orientation, is located in the region bordered by the Dohuk, Alqosh, and Dahqan anticlines from the north and south, respectively. Additionally, Wadi Bandawaya, which is formed by a collection of tiny parallel valleys, is moving towards this region from the bottom of the slopes in the western region of Jebel Zawita, and from the slopes situated on the eastern side of Jebel Zawa. A group of slopes flows from the northern slopes of Mount Alqosh, especially from the eastern side. The valley runs westward, parallel to Jabal Alqosh, and several small seasonal tributaries flow into it, which are fed by seasonal springs at the bottom of the mountain slopes. Then the valley penetrates the area between the mountains of Alqosh and Dahqan through a narrow strait towards the southwest, up to the Mosul Lake dam (Figure 2).

Figure 2 Map of the study area.

Al-Jawadi et al. (2020) investigated the structural and stratigraphic geological setting, the geotechnical characteristics of the rocks in the Bandawaya Valley basin according to the rock mass classification, the hydrological study of the dam, and the volume of water storage in accordance with the proposed storage levels. As a result, they recommended placing the water harvesting dam near the strait.

This study aims to evaluate the effects of springs and infrastructure on the waters of Wadi Bendawaya, and to identify whether they are suitable for drinking in the event that a water harvesting dam project is implemented in the area.

2 Materials and methods

Ten duplicate samples were collected from the waters of the Wadi Bandawaya along the path of the valley, and from the small streams that drain into it, as follows:

• BN1: stream near the western side of Zawita Mount (Brifka area),
• BN2: stream near the eastern slope of Zawa Mount,
• BN3: stream near the eastern slope of Alqosh Mount,
• BN4, BN5 and BN6: along the Bandawaya Valley,
• BN7: stream from Sharya village,
• BN8: the striate area,
• BN9: the tourist village,
• BN10: location before Mosul-Dohuk Road,
• BN11: near Mosul-Dohuk Road, and
• BN12: before Mosul Lake dam. (Figure 2).

All paired samples have physical and chemical properties that are analyzed using standard methods of water analysis (Abbawi and Hassan 1990). The acidity function (pH) was measured using HANNA PH211, and the electrical conductivity (Ec) by HANNA EC214, as well as measuring the turbidity (Tr) using a turbidity meter (Hanna HI 93703). Calcium and magnesium levels were determined by the titration method with EDTA, sodium, and potassium levels by flame spectrometry (Flame-photometer, type- JENWAY PEP7), while carbonates, bicarbonates, and chlorides were measured by titration methods. Sulfates and nitrates were measured using the colorimetric method using UV-spectrometry (UV – Spectrophotometer type – OGAWA, OSK 7724). The total dissolved salts (TDS) and total hardness (TH) were also estimated. The analyzes were completed in the Laboratory of Geochemistry in the Dams and Water Resources Research Center, University of Mosul.

The water quality index (WQI) represents the conversion of all data related to water quality into a mathematical number that expresses the level of water quality (Kumar et al. 2015; Leizou et al. 2017, and Udom et al. 2006) to determine the suitability of the water in the study area for purposes of drinking, civil, and agricultural uses. The WQI was calculated using all the above parameters and based on the standards of the World Health Organization (WHO 2006), according to Equation 1 (Gupta and Misra 2016). Table 1 shows the drinking water quality index scale.

Table 1 Drinking water quality coefficient scale (Gupta and Misra 2016).

Drinking water quality meter	Drinking water quality class
0 – 25	Excellent
26 – 50	Good
51 – 75	Poor
76 – 100	Very poor
>100	Not suitable for drinking

(1)

(for each parameter) (2)

Where:

Qi	=	qualitative evaluation of the parameter (Appendix 1),
Vm	=	measured value of the parameter from the chemical analysis samples,
Vi	=	theoretical value of the parameter taken from the standard tables, and its value is (0) for all parameters except (pH=7).
Vs	=	standard values for the parameter according to the standards of the World Health Organization (WHO 2006) for drinking water (Appendix 2).

(3)

Where:

Wi

=

Relative weight of the parameter (Appendix 3).

The equivalent per million (EPM) formula was used to determine the water balance, which represents the accuracy of the data by calculating the total of each cation and anion concentrations (Baird et al. 2017). Criteria used to classify water was dependent on the value of concentrations in EPM, such as sodicity, which is calculated to express the extent of sodium's effect on irrigation water, such as the percentage of sodium (SSP), the percentage of sodium adsorption (SAR), and the amount of residual sodium carbonate (Residual Sodium Carbonate, RSC), in addition to the percentage of magnesium (MAR) (Abbawi and Hassan 1990):

(4)

(5)

(6)

(7)

3 Results and discussion

The findings of the physical tests and chemical analyses performed on water samples taken from the Bandawaya Valley and its tributaries near the valley's entrance are shown in Tables 2 and 3.

Table 2 Physical and chemical parameters of the studied water samples.

mg/L	pH	Ec	TDS	TH	Tr.	Ca2+	Mg2+	Na+	K+	HCO3-	SO42-	Cl-	NO3-
BN1	7.5	710	331	320	2.6	62	18	39	3	248	30	54	5
BN2	7.4	702	334	330	2.2	74	24	48	6	275	43	60	9
BN3	7.5	775	374	354	1.2	52	32	30	3	250	29	46	6
BN4	7.7	523	246	266	1.2	46	24	28	4	191	86	33	5
BN5	7.3	787	410	308	1.3	56	41	5	2	268	67	8	4
BN6	7.4	952	515	336	1.7	59	43	12	5	278	101	19	6
BN7	7.3	927	485	324	2.1	61	42	6	5	275	96	13	8
BN8	7.2	870	465	355	2.5	62	42	11	2	296	66	17	3
BN9	7.2	825	447	343	2.3	64	38	9	4	290	77	17	4
BN10	7.2	973	530	372	2.5	66	51	17	6	307	103	25	7
BN11	7.3	985	542	364	2.3	68	46	12	5	310	118	21	6
BN12	7.2	964	533	378	2.4	72	43	10	6	318	85	15	8
Min.	7.2	523	246	266	1.2	46	18	5	2	191	29	8	3
Max.	7.7	985	542	378	2.6	74	51	48	6	318	118	60	9
Aver.	7.4	833	434	338	2.0	62	37	19	4	276	75	27	6

pH in Unit, Ec in µs.cm-¹, Tr. In NTU, the rest of the parameters are in ppm.

Table 3 Chemical parameters in meq/L of the studied samples.

	Ca2+	Mg2+	Na+	K+	Total	HCO3-	SO42-	Cl-	NO3-	Total
BN1	3.08	1.45	1.67	0.08	6.29	4.06	0.62	1.53	0.08	6.30
BN2	3.69	1.97	2.09	0.15	7.89	4.51	0.90	1.70	0.15	7.25
BN3	2.61	2.63	1.32	0.08	6.65	4.10	0.61	1.29	0.10	6.09
BN4	2.30	1.97	1.20	0.09	5.56	3.13	1.79	0.94	0.08	5.94
BN5	2.80	3.36	0.23	0.06	6.45	4.40	1.40	0.23	0.06	6.10
BN6	2.92	3.56	0.53	0.12	7.14	4.55	2.11	0.53	0.10	7.29
BN7	3.06	3.42	0.28	0.13	6.89	4.51	1.99	0.35	0.13	6.99
BN8	3.10	3.45	0.50	0.05	7.11	4.85	1.38	0.47	0.05	6.74
BN9	3.19	3.13	0.37	0.11	6.81	4.76	1.59	0.49	0.07	6.90
BN10	3.28	4.17	0.75	0.15	8.35	5.04	2.15	0.70	0.11	8.00
BN11	3.39	3.79	0.52	0.13	7.83	5.08	2.46	0.59	0.10	8.23
BN12	3.59	3.54	0.43	0.15	7.72	5.21	1.77	0.42	0.13	7.53

The pH levels of the water samples ranged from 7.2–7.7, with an average of 7.4 in Table 2, which is within the typical ranges for drinking and irrigation (7.0-8.5) (Abbawi and Hassan 1990, and WHO 2006). In rainwater, the process of dissolving gases, particularly carbon dioxide, usually results in a decrease in the acidic function, which is attributed to the activity of water infiltrated through the soil in the dissolution and washing activities, especially on carbonate rocks. A slight decrease in the acidic function values was observed. The values of the acidic function reflect the quantity of the dissolving process in carbonite minerals such dolomite in the Dolostone Pila Spi Formation and limestone in the Fat'ha Formation, as shown in Figure 3.

Figure 3 HCO₃^- reflects the pH value in the water samples.

In the study samples, the electrical conductivity ranges from 523-985, 833 µs.cm-¹, (Table 2) reflecting the number of dissolved salts in the water. These comparatively low values may be caused by the slow rate of carbonate component dissolution in the Pila Spi Formation limestone and dolomite rocks, which is dependent on the amount of carbon dioxide dissolved in rainwater that seeps into cracks and joints in the rocks.

The infiltrated water is retained within the carbonate rocks, allowing some of its components to dissolve and subsequently feed the Bandawaya valley through various springs in the region near the northern end of the slopes of Mount Alqosh and Mount Zawa. In addition to the Fat'ha Formation's gypsum dissolving, it is also exposed in some places. Figure 4 illustrates the significant correlation between the electrical conductivity values and the bicarbonate and sulfate concentrations.

Figure 4 Electrical conductivity correlated to HCO₃^- and SO₄^2- in the water samples.

TDS concentrations often represent the amount of dissolved minerals (salts) in the water, which regulate the assessment of the water's suitability for use, including irrigation, drinking, and watering animals. This is particularly true in closed subsurface bedrocks. The dissolution processes of the minerals that make up those bedrocks, such as carbonate minerals in the limestone rocks that form the highlands and the Fat'ha Formation rocks (limestone, marl, and gypsum) that are exposed at the bottom of slopes, are influenced by the water feeding from the mountainous region. The Alqosh and Zawa mountains, whose weathering byproducts are transported by surface water, increase the concentration of certain ions (Al-Youzbakey and Eclimes 2018). Chemical weathering and modifications to the stability conditions of the mineral phases are caused by the process of water infiltration through joints and cracks in the Pila Spi Formation's rock beds. This dissolution process involves the entry of water into the subsurface layers, the dissolution of carbon dioxide in rain, and the vital activity of plants and microorganisms. The TDS ranged from 246 to 542, 434 ppm, which often denotes a reduction in the impact of the dissolution process caused by rainwater infiltration, which increases suitability of the water for various uses. (Todd 1980).

The total hardness expresses the amount of dissolving mineral phases that are unstable due to the chemical weathering process under the acidic influence of carbon dioxide dissolved in rainwater, mainly in the carbonate phases. The total hardness values ranged from 266-378, 338 ppm. Table 2 shows that the hardness values somewhat increase along the valley's length, showing the impact of continual dissolution effectiveness on the valley's stripped carbonate components, which would increase the concentration of calcium that contributes to hardness. (Mustafa et al. 2017). Figure 5 confirms the clear, direct relationship between total hardness and calcium and magnesium concentrations in the Bandawaya Valley water samples.

Figure 5 TH correlated to the Ca²⁺ and Mg²⁺ in the water samples.

According to Table 2, the turbidity values are low (1.2-2.6, 2.0 NTU), and below their typical upper limits, which are 5 mg/L according to the World Health Organization (WHO 2006). The procedure for sampling was conducted in the late spring when rains had already stopped and there was no surface runoff to degrade the valley's sediments. Due to the huge catchment area in the basin within the valley, it is anticipated that the turbidity values will be high during times of heavy rainfall (Al-Jawadi et al. 2020).

Calcium concentrations range from 46-74, 62 ppm, which is higher than the rest of the other cations' average concentrations of 75 mg/L (WHO 2006). Figure 6 depicts a clear, direct correlation between calcium and bicarbonate concentrations, demonstrating their coexistence in the same mineral phases (calcite and dolomite) that make up the Pila Spi Formation rocks. The effect of carbon dioxide gas dissolved in rainfall is related to the effectiveness of these phases being dissolved. Table 2 also shows a relative increase in calcium concentrations along the valley's length, which is a result of carbonate components continuing to dissolve in the Bandawaya Valley and its minor tributaries.

Figure 6 Ca²⁺ correlated to the HCO₃^- in the water samples, reflecting the same mineral phase (dolomite & Mg-calcite) in the source rocks.

The range of magnesium concentrations (18-51, 37 ppm) is near to the natural limits. The Pila Spi Formation’s dolostone rocks, which include Mg-calcite and dolomite, are the source of magnesium (Figure 7). This is due to the presence of calcium in many mineral carbonate phases in the rocks of the Pila Spi Formation and the limestones in the Fat'ha Formation. Figure 8 demonstrates that there is no association between calcium and magnesium concentrations.

Figure 7 The strong correlation between HCO₃^- and Ca²⁺ + Mg²⁺ represent the same mineral phases (dolomite and Mg-calcite) in the source rocks.

Figure 8 The inverse relationship between Ca²⁺ and Mg²⁺ in water samples reflect the effect of dissolving dolomite, Mg-calcite in Pila Spi dolostone, and calcite in the Fat'ha limestone.

The sodium concentrations are in the range of 5-48, 19 ppm. It is believed that during precipitation, the slope of the region’s topography towards the course of the valley directs the infiltrated water through recent sediments and soil to the nearby sub-surface water. During hot and dry spells, water in the soil pores works to precipitate sodium chloride as secondary salts on the soil's surface by capillary action. These secondary salts are then exposed to dissolving and washing by rain and surface water to the valley's stream during the following rainy periods (Al-Youzbakey et al. 2018) (Figure 9).

Figure 9 The strong relationship between Na⁺ and Cl^- in water samples represents the halite phase as a secondary mineral in soil, and a primary mineral in the Fat'ha Formation within the gypsum layer.

Despite being one of the elements with high solubility and mobility, potassium levels are often lower than sodium. This is because clay minerals prevalent in soil and recent sediments can stabilize and adsorb potassium. Potassium concentrations in the waters of Wadi Bandawaya can reach 2–6, 4 ppm. The lack of secondary potassium halide salts in the soils surrounding the valley is indicated by the weak correlation between sodium and potassium in the study samples. Therefore, it is believed that the breakdown of synthetic fertilizers like N.P.K., which are often used in agricultural areas, is the main source of potassium. The high correlation between potassium and nitrate, the primary fertilizer ingredient, is shown in Figure 10.

Figure 10 The relationship between K⁺ and NO₃^- in water samples reflect the effect of dissolving chemical fertilizers in the soil.

Despite well water having a proportion of alkalinity indicated by bicarbonate ions, the acidic function did not exceed the limit (8.3), making it eligible to contain carbonates. (Mustafa et al. 2017). Bicarbonate is produced by the dissolving processes of the carbonate minerals in limestone. Bicarbonate levels in water samples were between 191-318, 276 ppm. Numerous factors, including the pressure of carbon dioxide gas, the acidity function, the quality of the limestone storage rocks, the temperature, and the presence of sulfates in the medium, regulate the amount of solute and hence the concentration of bicarbonate. (Deming 2002).

The study samples contain 29-118, 75 ppm of sulfate. The presence of exposed gypsum rocks from the Fat'ha Formation at the feet of Mount Alqosh and Mount Zawa is thought to be the source of the sulfate. The rocks' outcrop is affected by chemical weathering factors and dissolving processes caused by rain and surface water flowing through minor rivers into the Bandawaya Valley. However, these rocks are commonly in a state of equilibrium between the phases of the evaporites (gypsum) and the phases of carbonite (calcite and Mg-calcite), which are controlled by the ion concentrations and the pressure of dissolved carbon dioxide gas (Phillips and Castro 2004). As a result, there is no obvious direct correlation between their concentrations in water samples (Figure 11). During the wet seasons, the dissolution of rock fragments resulting from the erosion of exposed gypsum rocks in particular regions contributes to an increase in the concentration of sulfates in surface waters (Figure 12).

Figure 11 The relationship between HCO₃^- and SO₄^2- in water samples reflect the effect of dissolving Pila Spi dolostones and Fat'ha gypsum & limestones.

Figure 12 The minor sharing of the dissolving gypsum to the water quality.

Bandawaya Valley stream water samples have chloride values of 8-60, 27 ppm. Due to the dissolution of secondary sodium chloride salts in the soil surface, Figure 9 shows a significant relationship between the concentrations of sodium and chloride. Recent sediments and soil include sodium chloride, which precipitates as secondary salts as a result of the evaporation of water contained in the pores of the upper zone of the soil close to the surface by the activities of capillary action (Chapelle 2004). Furthermore, the surface runoff water from rainfall dissolved the sodium chloride salts easily because of their high solubility.

There are several sources of nitrates in water, including biological processes (such as sewage and animal husbandry), agricultural activity (such as organic and chemical fertilization) (Dikeogu et al. 2018), and rainfall (which is affected by bacteria in the soil) (Jones 1997). Nitrate concentrations range from 3-9, 6 ppm. However, Figure 10, which demonstrates the relation between potassium and nitrate concentrations, illustrates that nitrate fertilization, whether chemical or organic, is the most efficient way to add nitrates to water.

The main cation and anion concentrations along the Bandawaya valley's course show an almost relative increase (Table 2), which is caused by the continuous influence of chemical dissolution and weathering activities, whose products are transmitted through the small tributaries that flow into the valley's main course.

One of the most significant guidelines for evaluating water for drinking and household usage is set forth by the World Health Organization (WHO 2006) (Obiefuna and Sheriff 2011). All the physical and chemical properties are within the WHO-approved parameters. The Water Quality Index (WQI), a statistical method used to reduce a massive amount of water quality data to a single value denoting a degree of quality, was also used to classify the waters of the Bendawaya valley stream. Planning for land use and managing water resources in a region requires the usage of the WQI (Saeedir et al. 2010). According to the classification of Gupta and Misra (2016), the category for the use of water for drinking, is listed in Table 1. All water samples were determined to be good or almost excellent for drinking, according to Table 4. This is a reliable estimate of how much water the residents of small towns and villages near to the valley can allocate for domestic use.

Table 4 Water quality index (WQI) of the studied water samples.

S. No.	WQI	Class	S. No.	WQI	Class
BN1	31.84	Good	BN7	29.44	Good
BN2	31.81	Good	BN8	24.45	Excellent
BN3	37.07	Good	BN9	24.35	Excellent
BN4	38.85	Good	BN10	28.21	Good
BN5	27.35	Good	BN11	30.88	Good
BN6	33.04	Good	BN12	27.27	Good

It should be advantageous for plants, animals, and the food chain to use water for agriculture. As a result, the irrigation water's quality must be within the acceptable limits of the following irrigation classification parameters.

Sodium content is a key factor in the study of sodium risks. It is also used to assess the water quality for agriculture. In contrast to calcium and magnesium ions, which are less significant in the process of aeration and water absorption into the soil (Joshi et al. 2009), the high percentage of sodium in irrigation water may impede or harm plant growth and reduce soil permeability.

Numerous factors can be used to evaluate sodium's impact, including the soluble sodium percentage (SSP), which shows how much sodium is present compared to other cations, the quantity of residual sodium bicarbonate (RSBC), which measures the amount of sodium carbonate that precipitates as a result of the water's acidity and damages the soil, and the percentage of sodium adsorption (SAR), which measures the rate of sodium adsorption by the soil and influences the soil's capacity to hold water (Abbawi and Hassan 1990). Since all samples had an SSP below 60%, Table 5 shows that sodium generally has little impact on the characteristics of the Bandawaya valley water when used for irrigation (Todd 1980). The water was categorized as low sodium (S1) since the sodium adsorption rate does not exceed 2.5 (according to the American Salinity Laboratory). There was no impact from sodium content since all the water samples had residual sodium carbonate levels below 1.25 epm, making the water also suitable for irrigation (Abbawi and Hassan 1990).

According to the classification of Willcox (1948) in Todd (1980), which is based on Ec and Na%, the majority of well water is excellent-to-good for irrigation, since the values of Ec and Na% are less than 1000 and 60, respectively. The classification of water based on Ec and SAR shows that the waters of Wadi Bandawaya fall into the two fields: C2-S1, which is suitable for use in the field of irrigation, and C3-S1, which represents water suitable for irrigation, was supported by Richard (1954) in Abbawi & Hassan (1990). According to the magnesium absorption ratio (MAR) parameter, irrigation water is suitable for use if MAR values are less than 50. Magnesium is one of the significant ions that are included in the classification of irrigation water and its quality, and an increase in magnesium in the water has a negative impact on agricultural yield because the soil content will be more saline (Joshi et al. 2009). The Permeability Index (PI) values, which reflect the permeability of the soil affected by the long-term use of irrigation water, ​​lie between 27.4 – 32.8, and therefore the water is classified as suitable and within Class II (25 – 75%) (Obiefuna and Sheriff 2011). Kelly's ratio (KR) reflects the case of chemical equilibrium between the solubility of sodium and the solubility conditions of calcium and magnesium. If the KR values ​​in the water are less than (1.0) as in the present study, then the water is suitable for irrigation (Aghazadeh and Mogaddam 2010).

Table 5 Water classification parameters for irrigation purposes.

	SAR	SSP	RSBC	PI	MAR	KR
BN1	1.11	26.61	-0.47	32.76	31.94	0.37
BN2	1.24	26.44	-1.15	27.67	34.86	0.37
BN3	0.82	19.87	-1.15	31.02	50.16	0.25
BN4	0.82	21.49	-1.14	32.57	46.18	0.28
BN5	0.13	3.51	-1.77	32.84	54.53	0.04
BN6	0.30	7.49	-1.93	30.47	54.91	0.08
BN7	0.15	4.04	-1.97	31.46	52.75	0.04
BN8	0.27	6.97	-1.71	31.28	52.67	0.08
BN9	0.21	5.49	-1.56	32.64	49.46	0.06
BN10	0.39	8.95	-2.41	27.46	55.94	0.10
BN11	0.28	6.66	-2.10	29.34	52.74	0.07
BN12	0.23	5.63	-1.92	30.23	49.62	0.06

4 Conclusions 

The current study indicated that the waters of Wadi Bandawaya are freshwater, suitable for drinking and household use through the results of chemical analysis and the use of water classification standards for drinking and agricultural purposes.

Since the Bandawaya Valley is constantly flowing, and the flow fluctuates depending on the season's precipitation, the valley water can be stored in the water harvesting project by building a dam in the strait of the valley between Jabal Al-Qoush and Dahqan.

The Bandawaya Valley stream is fed by several high-quality springs, and their discharge is influenced by the annual rainfall.

When there is a fluctuation in precipitation, and plants require irrigation, it is possible to use the water held in the dam basin proposed to be built in the valley to irrigate the adjacent lands. In the event of low rainfall and fluctuating rainy periods, in addition to the employment of alternative irrigation techniques, it is also possible to use the water stored in the proposed dam basin to irrigate the adjacent lands in addition to the use of complementary irrigation methods in the event of a low rainfall and varying rain times.

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Appendix 1 (Qi)

Qi	pH	Ec.	TDS	TH	Ca2+	Mg2+	Na+	K+	HCO3-	SO42-	Cl-	NO3-
BN1	33.333	50.714	33.100	64.000	82.400	35.200	19.250	6.000	62.000	7.500	21.652	10.000
BN2	26.667	50.143	33.400	66.000	98.533	48.000	24.000	10.364	68.750	10.750	24.152	18.200
BN3	33.333	55.357	37.400	70.800	69.867	96.200	15.200	6.000	62.500	7.275	18.320	12.000
BN4	46.667	37.357	24.600	53.200	61.467	48.000	13.750	6.727	45.000	21.500	13.320	10.000
BN5	20.000	56.214	41.000	61.600	74.933	81.800	2.600	4.000	67.100	16.850	3.328	7.800
BN6	26.667	68.014	51.500	67.200	78.133	86.600	6.150	8.364	69.450	25.350	7.520	12.000
BN7	20.000	66.236	48.500	64.800	81.867	83.200	3.200	9.273	68.850	23.900	5.000	16.000
BN8	13.333	62.143	46.500	71.000	82.933	84.000	5.700	3.818	73.900	16.550	6.680	6.000
BN9	13.333	58.929	44.700	68.600	85.333	76.000	4.300	8.000	72.550	19.125	6.880	8.200
BN10	13.333	69.493	53.000	74.400	87.733	101.400	8.600	10.909	76.850	25.800	9.960	14.000
BN11	20.00	70.36	54.20	72.80	90.67	92.00	6.00	9.09	77.50	29.50	8.40	12.00
BN12	13.33	68.86	53.30	75.60	96.00	86.00	5.00	10.91	79.50	21.25	6.00	16.00

Appendix 2 (standard values)

pH	EC	TDS	TH	Ca2+	Mg2+	Na+	K+	HCO3-	SO42-	Cl-	NO3-
8.5	1400	1000	500	75	50	200	55	400	400	250	50

Appendix 3 (Wi values)

pH	EC	TDS	TH	Ca2+	Mg2+	Na+	K+	HCO3-	SO42-	Cl-	NO3-	Total
0.1176	0.0007	0.0010	0.0020	0.0133	0.0200	0.0050	0.0182	0.0025	0.0025	0.0040	0.0200	0.2069

Appendix 4 (Qi * Wi)

Qi*Wi	pH	EC	TDS	TH	Ca2+	Mg2+	Na+	K+	HCO3-	SO42-	Cl-	NO3-	Total
BN1	3.92	0.04	0.03	0.13	1.10	0.70	0.10	0.11	0.16	0.02	0.09	0.20	6.59
BN2	3.14	0.04	0.03	0.13	1.31	0.96	0.12	0.19	0.17	0.03	0.10	0.36	6.58
BN3	3.92	0.04	0.04	0.14	0.93	1.92	0.08	0.11	0.16	0.02	0.07	0.24	7.67
BN4	5.49	0.03	0.02	0.11	0.82	0.96	0.07	0.12	0.11	0.05	0.05	0.20	8.04
BN5	2.35	0.04	0.04	0.12	1.00	1.64	0.01	0.07	0.17	0.04	0.01	0.16	5.66
BN6	3.14	0.05	0.05	0.13	1.04	1.73	0.03	0.15	0.17	0.06	0.03	0.24	6.84
BN7	2.35	0.05	0.05	0.13	1.09	1.66	0.02	0.17	0.17	0.06	0.02	0.32	6.09
BN8	1.57	0.04	0.05	0.14	1.11	1.68	0.03	0.07	0.18	0.04	0.03	0.12	5.06
BN9	1.57	0.04	0.04	0.14	1.14	1.52	0.02	0.15	0.18	0.05	0.03	0.16	5.04
BN10	1.57	0.05	0.05	0.15	1.17	2.03	0.04	0.20	0.19	0.06	0.04	0.28	5.84
BN11	2.35	0.05	0.05	0.15	1.21	1.84	0.03	0.17	0.19	0.07	0.03	0.24	6.39
BN12	1.57	0.05	0.05	0.15	1.28	1.72	0.03	0.20	0.20	0.05	0.02	0.32	5.64