Field Study for the Assessment of the Water Losses Through the Open Irrigation Network Canals in Middle Egypt to the East Side of the River Nile

1. Introduction

One of the biggest challenges facing Egyptians recently has been bridging the fast-widening gap between the limited quantity of water that is currently available and the huge quantity required to meet the needs of growing populations for agricultural and food production. That is why Egyptian policymakers as well as scientific researchers in Egypt have focused on finding radical solutions for such a problem and providing the largest possible amount of water through more than one tool at the same time. In addition to proceeding with extreme degrees of rationalization of water use in all sectors, the National Great Project for Lining and Rehabilitation of All Open Canals of the Irrigation Network all over the Egyptian Countryside was recently implemented, mainly to get rid of the main reason for irrigation water losses through seepage in permeable soil. That project not only preserves the seeped quantities of water but also minimizes the lost quantities that were lost through evaporation and evapotranspiration due to controlling the designed cross-sections of all irrigation water streams. Also, the project stops the increase in water sections, distortions, or swimming processes, as well as the growth of weeds and plants in irrigation water canals, which decreases the lost quantities of water. The Egyptian irrigation authorities expect to save about five thousand million cubic meters of water a year. The current field study aims to evaluate the water losses from the Al Maanna canal network in Assiut governorate as a representative case study for the Middle Egypt region. Also, the study contains an economic study of the saved costs after the lining process in the selected study area.

2. Literature Review

Water losses from earthen irrigation canals have several forms; the most important of these, which have a significant impact on water quantities, are seepage, evaporation, and evapotranspiration losses, which will be described in more detail in the following sections:

2.1. Seepage Losses

Seepage losses from earthen irrigation canals, which account for a significant portion of canal water losses, are determined by several factors, such as soil permeability, canal water depth, length of wetted perimeter, channel geometry, location of the groundwater table, velocity of flowing water, and so on. Worldwide, several researchers studied seepage losses from the earthen canals, as given in the following Table 1.

Previous studies employed two basic strategies to quantify seepage losses from earthen canals: experimental formulas and field methods. A summary of these approaches is given below.

2.1.1. Experimental Formulas for Measuring Seepage Losses

The following Table 2 introduces a variety of experimental formulas that were used to quantify seepage losses from earthen canals.

2.1.2. The Field Ponding Method for Measuring of SEEPAGE losses

The field ponding method, which represents a direct method for measuring seepage losses from a considerable length of a canal, is based on restricting water in a certain reach of the canal and then measuring the water level twice: once after the restriction process and again after 24 hours. The reduction in the water level is considered a seepage loss (Leigh, 2014), as shown in Figure 1.

Leigh (2014) proposed the following equation to calculate the seepage rates of ponding tests:

$$\mathrm{S}=\frac{\mathrm{W}\ast \left({\mathrm{d}}_1-{\mathrm{d}}_2\right)\ast \mathrm{L}}{\mathrm{P}\ast \mathrm{L}}$$

(1)

where;	S	Average seepage losses from the ponded reach (ft3 /ft2 /day)
	W	Average width of water surface in the ponded reach (ft)
	d1	Water depth at the beginning of measurement in the ponded reach (ft)
	d2	Water depth in the ponded reach after 24 hours (ft)
	P	Average wetted perimeter in the ponded reach (ft)
	L	Length of canal ponded reach (ft)

2.2. Evaporation Losses

Evaporation losses from the open canals, which depend mainly on the surface wind speed, are negligible in comparison to seepage losses. Suhua et al. (2016) used two methods to investigate evaporation losses from the middle reaches of the Heihe River in northern China: i) the aerodynamic method based on the Double-Deck Surface Air Layer (DSAL) model, and ii) the heat balance method. Results showed that cumulative evaporation losses estimated by the DSAL model were equal in order of magnitude to those estimated by the heat balance method. The evaporation losses were determined to be less than 1% of the total designed discharge. They also provided the following equation to predict a canal's evaporation losses:

$$R=\left(K_{p\times }Ep\right)\ast W\ast L$$

(2)

where;	Ep	Pan Evaporation(mm/day)
	W	Width of water surface in the canal (m)
	L	Length of canal(m)
	Kp	Pan coefficient

2.3. Evapotranspiration Losses

Transpiration from the crops and evaporation from the soil make up the evapotranspiration in a cropped area. The evapotranspiration rate (crop water use) is determined by the crop type, growth stage, soil moisture content, and available energy to evaporate water (El-Enany et al. 2004). The reference crop evapotranspiration (ET_o) and an average crop coefficient (K_a) are used to calculate crop water use (ET_c) (Hanks, 1974), as follows:

$${\mathrm{E}\mathrm{T}}_c={\mathrm{K}}_a\ast {\mathrm{E}\mathrm{T}}_o$$

(3)

The average crop coefficient (K_a) is estimated, as follows (Paul, et al., 1993):

$${\mathrm{K}}_a=\left({\mathrm{K}}_{cb}\ast {\mathrm{K}}_s\right)+{\mathrm{K}}_w$$

(4)

where;	Ka	Average crop coefficient
	KCb	Basal crop coefficient
	Kw	Wet soil evaporation
	Ks	Water stress factor

On the other hand, Jensen et al. (1990) examined 20 methods to estimate ETo for arid and humid areas. For both areas, they found that the Penman-Monteith technique was the most accurate. The approach introduced by El-Enany et al. (2004) is used to calculate the water consumption (evapotranspiration losses) from a cultivated area as follows:

$$\mathrm{W}\mathrm{C}=\left(\frac{{\mathrm{E}\mathrm{T}}_{\mathrm{O}}{\ast \mathrm{K}}_{\mathrm{a}}\ast \mathrm{A}}{1000}\right)\ast \frac{4200}{86400}$$

where;	WC	Water consumptive needed during a month (m3/sec.)
	ETo	Monthly reference crop evapotranspiration (mm/day)
	Ka	Monthly average crop coefficient
	A	Area cultivated (feddan)

3. Research Methodology

Assessment of water losses from the distorted irrigation networks in Assiut Governorate, as well as the positive impacts of the rehabilitation process, will be conducted through the following steps: i) Selection and description of a study area; ii) Surveying of soil types in the study area; iii) Collection of meteorological data that affects evaporation and evapotranspiration losses; iv) Collection of field data that affects seepage, evaporation, and evapotranspiration losses; v) Analyses and discussions of seepage, evaporation, and evapotranspiration losses (before and after rehabilitation); and vi) An economic study of the saved costs after the lining process in the selected study area.

3.1. Selection and Description of the Study Area

Al Maanna Canal is one of the main canals in Assiut Governorate. It takes its water from the Eastern Naga Hammady Canal and irrigates a cropped area of about 13500 feddan. The length of the Al Maanna Canal is roughly 32.8 km. This length is divided into five reaches, where the less ordered canals are branched on both sides, as shown in Figure 2. The branches have a total length of around 47 km (Abu-Zaid and Sabery, 2021). Table 3 summarizes the characteristics of the Al Maanna Canal and its branches.

3.2. Surveying of Soil Types in the Study Area

It was required to take some samples along the canals' paths to determine the soil type, degree of permeability, and other physical properties. Every five kilometers along the main canal and one sample for every off-taking canal, soil samples were gathered at various depths beneath the canal bed and from the side slopes. All of these samples were subjected to sieve analysis, a liquid limit, a plastic limit, a plasticity index, and a group index test to estimate all of these parameters and coefficients.

3.3. Meteorological Data

Table 4 shows the available monthly meteorological data for the understudied region from the Arab Al-Awamer Weather Station (AAWS, 2020). These data include Air Temperature (T), Relative Humidity (RH), Pan Evaporation (Ep), Wind Speed, and Number of Sunny Hours per Day (SH/Day). These meteorological data were used to calculate evaporation and evapotranspiration losses from the Al Maanna canal and its branches, as analyzed and discussed further below.

3.4. Field Data

The gathered data from the study area of the Al Maanna canal and its branches were based on the required parameters to measure seepage, evaporation, and evapotranspiration losses from the network, as indicated below.

3.4.1. Field Parameters of Seepage Losses

In order to measure seepage losses, water was restricted in significant lengths of the Al Maanna canal and its branches using the field ponding method, as shown in photo (1); then the water level was measured twice, once after the restriction process and again after 24 hours, using the measuring device shown in photo (2). The ponding test seepage rates were calculated using the above-mentioned equation (1) proposed by Leigh (2014).

3.4.2. Field Parameters of Evaporation Losses

Evaporation losses occur from both the designed (rehabilitated) and distorted cross sections of canals, depending on the top width of the exposed water surface. As shown in Figure 3, if the top water surface in the distorted cross section is bigger than the top water surface in the designed cross section, the evaporation rate from the distorted cross section of the canal will be positive (more than the evaporation rate from the designed cross section). However, if the top water surface in the distorted cross section is less than the top water surface in the designed (rehabilitated) cross section, as shown in Figure 4, the evaporation rate from the distorted cross section of the canal will be negative (less than the evaporation rate from the designed cross section). The distorted cross sections of Al Maanna canal and its branches were measured every 200 m along the canal's length and compared with the designed cross sections. The evaporation rates from the designed and distorted cross sections were estimated using the foregoing equation (2) provided by Suhua et al. (2016), associated with the meteorological data listed in the above Table 4.

3.4.3. Field Parameters of Evapotranspiration Losses

Most irrigation canals have extensive weed growth along their sides as well as siltation above the canals' beds. These conditions have an impact on the hydraulic characteristics of canals, such as the shape of the cross-section and its performance, the reduction of water velocity, and the limiting capacity of irrigation canals. As shown in Photo 3, growing weeds along the banks of the Al Maanna canal and its branches is a source of evapotranspiration losses from the network. The weeds' dimensions were estimated using a field measuring wheel, as shown in Photo 4. The areas of weeds along Al Maanna Canal and its branches were computed using these dimensions, as given in Table 5.

The above-mentioned equation (5), developed by El-Enany et al. (2004), was used to estimate evapotranspiration losses from the weeds along Al Maanna canal and its branches, based on the available meteorological data introduced in the above Table 4, in addition to the CROPWATER software model that was utilized to estimate the reference evapotranspiration (ET_o) from the weeds. It's worth noting that the CROPWATER software is based on the Penman-Monteith method (Allen et al. 1998).

3.5. Analyses and Discussions

The determination of seepage, evaporation, and evapotranspiration losses from the distorted and designed (rehabilitated) cross sections of the Al Maanna canal and its branches in Assiut governorate was achieved by using the literature review associated with the collected data for the study area. The following items have been separately analyzed to determine each water loss from the network:

3.5.1. Seepage Losses

As shown in the Figure 6 and Figure 7, seepage losses from the distorted cross sections of Al Maanna canal and its branches were calculated using the field ponding method in addition to the experimental formulas presented in the foregoing Table 2.

From Figure 6, it can be observed that the maximum seepage losses from the Al Maanna canal occurred from the first reach, using the Offengenden experimental formula. Using the Indian experimental formula, the fourth reach had the lowest seepage losses.

From Figure 7, it can be noticed that the maximum seepage losses from the branches of the Al Maanna canal occurred from branches of the second reach using the Indian experimental formula. While, branches of the last reach caused the minimum seepage losses according to the Pakistani experimental formula. It should be noted that the first reach of the Al Maanna Canal has no branches.

The predictions of the experimental Moleth-Worth and Yennidunia formulas for measuring seepage losses are compatible with the field ponding method, as shown in Figure 6 and Figure 7. Seepage losses from the distorted cross sections of the Al Maanna canal were estimated to be about 1,562,917 and 1,617,354 m³/month by using the experimental Moleth-Worth formula and field ponding method, respectively. Seepage losses from the branches of the Al Maanna canal were estimated to be nearly 506,777 and 580,233 m³/month by using the Moleth-Worth formula and ponding method, respectively.

After the lining and rehabilitation process of the Al Maanna canal and its branches, the field ponding method was conducted to estimate seepage losses from the lined cross sections, as illustrated in the following Figure 8 and Figure 9.

The highest seepage losses from the rehabilitated sections of Al Maanna Canal occurred in the first reach, as shown in Figure 8. The fourth-lined reach had the fewest seepage losses. Also, Figure 9 shows that lined branches in the second reach of the Al Maanna canal caused the most seepage losses. While the last reach's lined branches caused the least amount of seepage losses.

The calculated seepage losses from the distorted cross sections and the rehabilitated sections have a clear difference. After the lining and rehabilitation process of the Al Maanna canal network, the massive amounts of seepage losses were significantly reduced to about 472,255 m³/month, which represents nearly 21.48% of seepage losses before rehabilitation.

3.5.2. Evaporation Losses

Evaporation losses from Al Maanna canal and its branches obtained from the distorted and rehabilitated sections show a clear difference, as shown in Figure 10 and Figure 11. Evaporation losses from the lined (designed) sections are lower than those from the distorted (earthen) sections due to the decreased top width of the exposed water surface in the rehabilitated sections.

Also, it should be noted that branches of the last reach have negative evaporation losses, as shown in Figure 11, which is considered an indication of decreasing the distorted cross sections compared to the lined sections in these branches. Evaporation losses from the distorted sections of the Al Maanna canal and its branches were estimated to be around 60,789 and 24,899 m³/month, respectively. While, evaporation losses from the lined sections of Al Maanna canal and its branches were estimated to be about 51,856 and 22,905 m³/month, respectively. As a result, evaporation losses can be reduced by roughly 10,926 m³/month due to the rehabilitation of the Al Maanna canal network.

3.5.3. Evapotranspiration Losses

The first reach of the Al Maanna canal had the highest evapotranspiration rate from weeds, about 235,630 m³/month. While the minimum evapotranspiration rate from weeds occurred in the fourth reach, at about 73,634 m³/month, as presented in Figure 12.

These massive evapotranspiration losses caused by weeds along the banks of the Al Maanna canal and its branches will be ignored following the lining and rehabilitation process.

3.6. An Economic Study of the Lining Process in the Study Area

The traditional irrigation networks suffer from two main issues: (i) the growth of weeds along the banks of canals; and (ii) bed backfill. Weed removal occurred every three months, and canal dredging from bed backfill occurred once a year. For canals with a designed bed width of 10 m, weed removal costs approximately 5000 Egyptian pounds per km (LE/km), while bed dredging costs approximately 8 LE/m³ (MWRI, 2019). The total costs of bed dredging and weed removal from the distorted cross sections of Al Maanna canal and its branches are calculated and presented in the following constructed Table 6 and Table 7.

Weed removal occurs every three months, so the total annual cost of weed removal from Al Maanna Canal and its branches is approximately 1,498,773 LE per year.

According to the results of the above tables, the costs of bed dredging from the Al Maanna canal and its branches are approximately 5,304,030 and 533,363 Egyptian pounds, respectively. The costs of weed removal from Al Maanna Canal and its branches are approximately 573,393 and 925,380 Egyptian pounds per year. These costs can be saved after the lining and rehabilitation processes.

4. Conclusions

• After studying the seepage, evaporation, and evapotranspiration losses from the distorted and lined sections of the Al Maanna canal and its branches, the following main conclusions can be drawn:
• Using the most popular available equations for calculating the expected values of seeped water from the Al Maanna Canal, the obtained results were significantly different. This is due to the different conditions and properties of the soil in which the experiments were conducted, which produced each equation.
• The results obtained using the Moleth-Worth formula were the most compatible with the measured seeped quantities of water by the field ponding method. The measured seeped quantities from Al-Manna canal were about 1.563 million m³/month, while the calculated quantities using the Moleth-Worth equation were 1.617 million m³/month. Also, the seepage losses from the Al Manna canal branches were approximately 0.506 and 0.580 million m³/month, respectively, indicating an acceptable approximate difference.
• The maximum calculated evaporation and evapotranspiration losses calculated from Al Maanna Canal were approximately 0.061 and 0.736 million m³/month, respectively. While the maximum evaporation and evapotranspiration losses from the branches of the Al Maanna canal were calculated to be about 0.0249 and 0.397 million m³/month, respectively.
  The expected total seepage, evaporation, and evapotranspiration losses from the Al Maanna canal network might be about 3.42 million m3/month, which accounts for approximately 13.63% of the total discharge of the Al Manna Canal, which is so big.
• After the lining process, the field ponding method was employed to estimate seepage losses from the Al Maanna canal and its branches, which were about 0.472 million m3/month. Also, evaporation losses after the rehabilitation process can be reduced to around 0.075 m³ per month, while evapotranspiration losses will be neglected.
• The lining of distorted sections of the Al Maanna canal and its branches can reduce water losses by approximately 84%, which is good and sufficient to recommend and encourage the lining processes, where the gained quantities of water are more valuable and important than the cost of implementation.
• Saving not less than 5.84 Million L.E./year and 1.50 million L.E./year on the expenses of the regular periodic maintenance and weed removal costs for distorted Al Maanna canal sections and branches.