Archaeo-Hydraulic Investigations of the Ancient Water Supply System in the Lorestan Province

Abstract

Excavations in Iran’s Lorestan province uncovered a 200-year-old water system consisting of four earthenware jars connected by clay pipes, each jar built from six or seven pottery sections. Due to local conditions, the dimensions and spacing of the jars in this water supply system design deviate from the established standards in historical water science literature (a diameter-to-length ratio of less than 1:4). This deviation prompted detailed archaeo-hydraulic investigations, including fieldwork analyses and hydraulic calculations of the discovered water supply system. The system was designed to serve both public and governmental purposes. Structural modifications (diameter-to-length ratio < 1:4) improved durability and strength for regional conditions. The jars divided, ventilated, and filtered water from mud and sand. Comparative analyses suggest the water supply system dates to the late Zand and Qajar periods (18th–19th centuries).

1. Introduction

Located between 25° and 40° north latitude, the Iranian Plateau experiences minimal precipitation and increased drought risk due to its position within a high-pressure zone. Despite being home to 3% of the world’s population, the region receives only 1% of global freshwater with annual rainfall roughly one-third of the global average. This arid and semi-arid climate has made effective water management essential for sustaining civilizations throughout its history [1].

In Iran’s history, architecture has consistently integrated with water resources, reflecting the deep understanding of natural elements and the importance of water in sustaining life and civilization. Archeological evidence shows that Iranian engineers skillfully utilized topography, underground resources, and regional geography to construct water canals, using precise slope measurements to ensure effective flow to residential and military sites [2]. A notable example is the water supply system discovered in Boroujerd, Lorestan Province.

Early urban settlements developed secure and reliable water supply systems to withstand frequent invasions. Water tunnels, known as Sinnors, were in use in Palestine as early as 1200 BC [3].

One of the oldest water monuments discovered in Iran was the water supply system of the Choghaznabil Temple, located 30 km southeast of Shoosh (Susa) and 80 km north of Ahvaz in Khuzestan Province (southwest of Iran), dating back to about 3200 years ago. This temple boasts hydraulic facilities, like a reservoir, water channels, and a pond, ensuring the water needs of city dwellers [4]. Water resource management was a central priority during the Achaemenid period, marked by the construction of subterranean canals and large-scale public works. King Cyrus built the Ramjerd Dam on the Kur River and the Jamshid canals to irrigate the Marvdasht plain in Fars Province. King Darius praised Governor Godates for promoting vegetation in northwest Asia to enhance the empire’s prosperity [5]. The emergence of Islam in Iran brought significant changes to religious practices, politics, and architecture. Crucially, qanats (a system for transporting water from an aquifer or well to the surface through an underground aqueduct) and water systems were preserved, as Muslims placed great importance on maintaining vital economic structures such as aqueducts [4,5,6]. Moreover, architects incorporated water into Iranian architecture by acknowledging the physical laws governing water and understanding its connection to human life and settlements’ development. Water has been a prominent feature in most Islamic buildings, representing centrality and unity in architecture. Over time, the imagery of springs, as described in the Holy Quran, became an inspiring model for architects [7]. Each water supply system has served distinct functions. Hence, it is crucial to explore them through the lenses of archeology, architecture, hydrology, hydraulics, and related disciplines.

In the Qajar period (1795–1925), clay pipes were employed in certain cities for water distribution networks, running horizontally in clay cement. This cement, once dried, forms an impermeable layer. Though the depth of clay pipe placement, (known as tanbushe in farsi), does not exceed a few meters, these pipes have proven durable for many years. Various cities benefitted from a reliable water system provided by the clay pipeline network, delivering potable water through urban streams along alleys and streets [8,9]. The water distribution system commonly relied on tanbushe.

The number of remaining historic water supply systems is quite limited. In Iran, these systems have faced ongoing destruction due to being frequently targeted by different ethnic groups.

The ancient water supply system discovered in the Lorestan province, Iran, is a previously undocumented structure in international scientific literature. Its components and their unique arrangement suggest a special functional design. To gain insight into its mechanism, this study innovatively combines water engineering with archeology, offering a more thorough understanding. Combining archeological knowledge with hydraulic engineering, referred to here as archaeo-hydraulic investigations, can clarify ambiguous aspects and shed light on both general and specialized features of the ancient water supply system. This marks the first investigation of this recently identified water structure, potentially enabling more in-depth future studies. Also, a key innovation of this study is its numerical calculation method tailored to the water supply system characteristics, enabling a more logical determination of its purpose and use.

This discovered system is uniquely structured. Thus, its scientific and technical study is important. Analyzing the system’s engineering and construction provides insights into ancient water supply structures. This research clarifies the design and purpose of the water supply system by addressing the following questions:

(1)

What was the intended function of this water infrastructure?

(2)

How did jars contribute to the identified water supply system?

2. Managing Water Resources and Drinking Water in Iran: A Historical Perspective

Numerous researchers have investigated water transfer systems in Iran and their mechanisms [10,11,12,13]. Some have specifically focused on “qanats”, exploring their history, construction methods, and components, and clarifying the process of water conveyance from trenches through canals and dams. Other studies provide detailed insights into the traditional material, known as Kaval, a large tanbushe used as a covering in qanat galleries and water conveyance systems [14], detailing its preparation and application. Fakhar Tehrani [10] specifically examined the primary materials employed in aqueduct construction.

Furthermore, researchers have also explored topics such as hydrology, water resources, qanats, canals, sealing bridges, and water channels using clay pipes for installation [1,12]. A comparative structural analysis [15] of water transfer methods in specific systems in Isfahan examined various types of water wheels and cow-powered water wheels (Gav-Chah or a well from which water is drawn by a cow), along with related elements in historic structures, illustrating diverse approaches to surface and groundwater transfer. This study [15] revealed the utilization of water transfer and sewage disposal systems in ancient edifices, showcasing varied forms based on water access, quantity, and storage sources.

Some researchers have also focused on the water supply network designed in the Nogonbad desert caravanserai [16]. This study was based on the results obtained from the archeological survey of the Nogonbad-Arkan region in Nain (located near Isfahan). The results revealed that engineers constructed a canal to transfer water to the accommodation centers, taking into account the topographic status, ground slope measurement, groundwater resources, and geographical location. Two notable techniques involved the construction of a stone canal to carry water from a spring located seven kilometers from Ain al-Rashid Caravanserai, and the establishment of a water transmission network using the qanat system, which involved using tanbushes to transport water to the Nogonbad residential complex over a distance of 15 km. These achievements showcase Iranian engineers’ expertise in water extraction, transmission, storage, and distribution technologies. The stony canal was erected during the late Timurid period (1370–1506) and functioned as a water transmission network in the Mongol era (1206–1294), overseen by Iranian ministers. This construction was used until the end of the Qajar period (1794–1925).

To illustrate the pre-modern water paradigm, consider the agricultural practices in Iran, which were managed for over 3000 years. In response to living in mountainous areas and dry regions, residents developed a system to collect snowmelt water through the channels they made underground known as qanats. The qanat started in the mountains, and the channels water down to grasslands, farms, gardens, and towns, rlying on gravity for flow [17]. The channels typically had a width of 50 to 80 cm and a height of 90 to 150 cm. The length varied from several hundred meters to more than 100 Km. This irrigation system, based on original knowledge and experimental hydrology, was a remarkable engineering achievement.

Water was channeled into towns through “qanats”—systems for transporting water from aquifers or wells to the surface through underground aqueducts or channels [18]. Benefiting from qanats, numerous significant cities emerged in central Iran. This is why the culture centered around the utilization of qanats, also known as Kariz (qanat), is dubbed “Kariz Civilization” or “hydraulic civilization”. The construction of qanats had a positive social impact by generating job opportunities within the local community. It is crucial to note that qanat systems play a significant role in influencing local communities regarding the organization and utilization of their water resources, especially for agricultural purposes [19]. To avoid any conflict between farmers, many different methods were employed to measure water distribution. One of the optimal ways to gauge the distributed water volume from the Zayandehroud river for agricultural purposes was pioneered by Sheikhbahayee, an Iranian scientist, with his technique known as Tumare Shikhbahayee [20].

Another method utilized to create underground water reservoirs for drinking water in ancient Iran is Ab Anbars (a traditional reservoir or cistern of drinking water in Greater Iran in antiquity). These structures were designed to meet the water requirements of caravans and local residents. The reservoir was typically located in a dry region and occasionally employed wind towers to maintain the coolness of the water within this cylindrical reservoir. The components utilized in constructing these reservoirs included a blend of sand, clay, egg whites, lime, goat hairs, and ash, known as sarooj (a traditional water-resistant mortar used in Iranian architecture, used in the construction of bridges and yakhchāl, ancient Persian ice houses). The bricks utilized for constructing this storage were crafted in a specific manner and were referred to as Ab Anbar bricks. Iran has a long history of dam building. The process involved three vital steps: selecting an optimal location, assessing the foundation conditions, and choosing suitable materials. They carefully considered the design and the technology, and the river diversion during the construction of dams. There are various kinds of dams, including gravity dams, arch dams, and buttress dams. The construction of contemporary dams commenced around three decades ago [21]. The construction of dams and reservoirs along rivers from Alburz and Zagros mountains in Iran has boosted the utilization of surface water. In the central, northeastern, and southern regions of the country, groundwater serves as the primary source of drinking water [22,23]. An examination of the pre-modern era reveals that the traditional water paradigm reflects the interconnectedness between humans and nature.

3. Water Supply System in the Historical District of Boroujerd City

Boroujerd is one of the ancient cities of the Islamic era, with an urban center dating back to at least the third century Hijri (ninth century AD) [24]. It experienced growth during the Zandieh dynasty (1751–1794) and thrived in the Qajar era, reaching its peak of prosperity. By 1850, the city had 40,000 inhabitants in 12,000 homes. The city is located on a flat terrain, surrounded by defensive towers and fortifications. In addition, several gates are placed around the boundaries (Figure 1). Boroujerd city consists of two primary sections: the citadel and the city. The citadel, also referred to as the fort, covers the western portion of the city. It is large and surrounded on three sides by residential areas of different sizes and compositions. This area includes the Yakhchal neighborhood located along Shohada Street, Baghe-e-Shah, and Ghadghon neighborhoods. A military square resided in the center of the citadel, surrounded by artillery and military barracks, a gunpowder depot, and a group of gardens called Baghe-e-Shah or Khold-e-Barin (Paradise). These gardens occupied half of the citadel’s space. The fortifications connected to the city through the citadel gate. Furthermore, these fortifications were linked to Khorramabad city (Lorestan province’s capital) and its surroundings through the Soozani gate. Over time, neighborhoods emerged around the citadel with their own focal points. Yet, there was no organized layout or street plan in place. The inhabitants built their dwellings within the city center, resulting in the development of a distinct architectural scheme [24].

A distinctive water supply system was discovered on the southern wall while excavating a plot of land on Hafez Street situated within the citadel (Figure 2) [26].

4. Fieldwork Analysis of Water Supply System

The water supply system is located at a depth of 80 cm from the surface. The system comprises four big clay jars linked by clay pipes (Figure 3A). An integral component of this system is a sizeable clay pipe (40 cm in diameter, extending from north to south (Figure 3B)).

This pipe likely carried water from the city’s north to its south.

There is a structure consisting of clay jars. The main structure begins at a depth of about 1.25 m, extended to 2.40 m below the surface. The clay pipes, inclined from west to east, are divided into sections, each containing six to seven interconnected pipes (diameter = 33 cm). (Figure 4A,B). These pipes end in large vase-shaped earthenware containers known as jars (Figure 4C). Each jar is encircled by brick lines (Figure 4D).

The complexity of the mentioned water supply system was due to the change in pipe usage in the secondary stage, in a way that some parts were blocked with new pipes or intentionally filled with large jars. A 15–20 cm layer of dark mortar sealing the clay jar seams to prevent separation from water pressure. The texture of this solid mortar reveals it is made of lime, clay, and sand. A 5 cm layer of mud has accumulated inside the pipes. Additionally, Figure 5 shows an even deposit covering the interior surface of the large jars. Figure 6 depicts the discovered system. Today, it is not possible to determine the exact location of the water source used in this system without conducting archeological excavations. In 1850, Etemad-ol-Saltaneh, accompanying Naseredin-shah (the Qājār shah of Iran from 1848 to 1896) to Boroujerd, noted the qanat north of the city, which served as the primary source of drinking water for Boroujerd during the Qajar period [28].

Jars in the water supply system may have functioned similarly to aeration wells (Figure 7). Despite design differences arising from their above- or below-ground locations, both structures aerated the water supply system. Given the system’s air transfer capacity and structural sensitivity, the jars in the discovered water supply system are less than 50 m apart. Furthermore, the close spacing of the clay jars also allows them to function as water dividers (Figure 6 and Figure 8).

Large jars in clay pipe systems can help settle mud and sand from water flow, resulting in cleaner water. In the past decades, after water had passed through the clay pipes and reached the fountain pond, a clay jar was also placed under the fountain (Figure 9). This permitted the sediment to settle in the clay jar prior to entering the fountain’s channel [30].

Large jars and ventilation wells are frequently utilized in the design of water dividers, sludge receivers, and aeration of flow paths.

In recent years, clay pipe structures from the Qajar period have been discovered in Abbasabad, Behshahr, Mazandaran Province (Figure 10). The water supply system in Borujerd’s government citadel likely dates to the Zand and Qajar periods, based on the citadel’s construction timeline.

Figure 8. The installation of jars along the flow path helps to distribute water [31].

Figure 8. The installation of jars along the flow path helps to distribute water [31].

Figure 9. Method of connecting the clay pipes, the jar, and the fountain (vertical pipe) [32].

Figure 9. Method of connecting the clay pipes, the jar, and the fountain (vertical pipe) [32].

Figure 10. The clay pipe in the bath of the Abbasabad Behshahr complex [33].

Figure 10. The clay pipe in the bath of the Abbasabad Behshahr complex [33].

5. Hydraulic Analysis of Water Supply System

In a hydraulic cross-section, the water velocity varies with distance from the bed. In open channels, this variation occurs vertically. The correction factor for converting surface velocity to average velocity is determined by the vertical velocity profile. In laminar flow on a smooth surface, the parabolic velocity profile can be theoretically determined. Roughness elements alter the vertical velocity profile shape. Accordingly, achieving accurate mean flow velocity measurements requires setting a suitable correction factor (αv) for varying hydraulic conditions. Several studies have investigated various conditions and established correction factor values: α_v = 0.67 for laminar flow and α_v = 0.8 for turbulent flow. This study uses a correction factor of 0.8 [34,35] if a surface velocity of 25 cm/s is utilized.

Therefore, the average velocity V is calculated as

$$V={\mathsf{\alpha }}_{\mathrm{v}}\times V_s=0.8\times 25=20\mathrm{c}\mathrm{m}/\mathrm{s}$$

(1)

However, the surface velocity (V_S) increases on sloped ground compared to flat ground. To maintain water quality and prevent sediment buildup in drinking water systems, the water velocity should exceed 0.3 m/s [36]. Similarly, assuming clay pipes are non-erosive closed channel, to prevent the settling of suspended materials in non-erodible covered channels, a minimum permissible velocity must be maintained. Additionally, the velocity also prevents algae and aquatic plant growth, thus maintaining a uniform flow by avoiding cross-sectional deformation from silt deposition or excessive plant proliferation. Consequently, non-erosive channels are designed with a minimum velocity of 0.6 to 0.9 m/s [37].

Thus, assuming the 33 cm diameter circular clay pipes of the water supply system are completely filled with water from bottom to top, and water flows at a velocity of 0.9 m/s in the east–west direction, the wetted cross-sectional area $A$ and the volume of flowing water Q resulted in

$$\mathrm{A}=1.82\times {12.99}^2=307.1{in}^2$$

$$V=0.9{\displaystyle \frac{\mathrm{m}}{\mathrm{s}}}$$

$$\mathrm{Q}=V\times A=(0.9\times 307.1)/3600=76{\displaystyle \frac{\mathrm{L}}{\mathrm{s}}}$$

(2)

The larger clay pipe, measuring 40 cm in diameter and oriented north–south in the water supply system, resulted in a water flow rate of

$$\mathrm{Q}=1.82\times V\times D^2=(0.9\times 451.3)/3600=112{\displaystyle \frac{\mathrm{L}}{\mathrm{s}}}$$

(3)

Experimental equations for canal design, like the Gauckler–Manning equation, consider the balance between gravitational forces that propel water and frictional forces that resist its flow. The Gauckler–Manning equation was proposed by Philippe Gaspard Gauckler in 1867 and later re-developed by Robert Manning in 1890 [38,39]. This equation is

$$\mathrm{V}={\displaystyle \frac{1}{n}}\times R^{{\displaystyle \frac{2}{3}}}\times {S_f}^{1/2}$$

(4)

where “$V$” represents the average velocity, “$R$” (calculated as A/P) is the hydraulic radius, “$P$” is the wetted perimeter, “$n$” is the Gauckler–Manning coefficient, and “$S_f$” is the stream slope or hydraulic gradient. If “$V$” is in m/s and “$R$” in m, then “$n$” is in s/${\mathrm{m}}^{1/3}$). When the cross-section is complete, A = πr² and P = 2πr, where “r” is the radius. The stream slope for the discovered water supply was estimated in 0.006 from field measurements, and the Gauckler–Manning coefficient for clay pipes is about 0.013. The clay pipes are connected, and the pipeline is uneven. It can be considered a range of the Gauckler–Manning coefficient equal to [0.011–0.015].

According to Equation (4), the velocity and flow rate in a pipe with a diameter of 33 cm (A = 0.085 m²) are

V = 1/0.013 × ((3.14 × 0.165²)/(2 × 3.14 × 0.165))^0.66 × 0.006^0.5 = 1.148 m/s = 114.8 cm/s

(5)

$$Q={\displaystyle \frac{1}{n}}\times ({\displaystyle \frac{A^{\frac{5}{3}}}{P^{\frac{2}{3}}}})\times {S_f}^{{\displaystyle \frac{1}{2}}}=0.097{\mathrm{m}}^3/\mathrm{s}=97\mathrm{L}/\mathrm{s}$$

(6)

Also, the velocity and flow rate for the 40 cm diameter pipes (A = 0.1256 m²) are

V = 1/0.013 × ((3.14 × 0.20²)/(2 × 3.14 × 0.20))^0.66 × 0.006^0.5 = 1.3 m/s = 130 cm/s

(7)

$$Q={\displaystyle \frac{\mathit{1}}{n}}\times \left({\displaystyle \frac{A^{\frac{5}{3}}}{P^{\frac{2}{3}}}}\right)\times {S_f}^{{\displaystyle \frac{1}{2}}}=0.163{\mathrm{m}}^3/\mathrm{s}=163\mathrm{L}/\mathrm{s}$$

(8)

Forms of the Hazen Williams Equation for Water Flow Rate for Pipe Sizes. The Hazen Williams equation is sometimes expressed as an equation for velocity in the pipe and sometimes as an equation for pipe flow rate. It also can be expressed in terms of the pipe head loss or the frictional pressure drop [40].

As an equation for velocity, the traditional form of the Hazen Williams equation is in S.I. units

$$\mathrm{V}=0.85\mathrm{C}\times {\mathrm{R}}^{0.633}\times {\mathrm{S}}^{0.54}$$

where

• V is the water flow velocity, m/sec,
• C is the Hazen Williams coefficient, dimensionless (depends on pipe material and age),
• R is the hydraulic radius, m (R = cross-sectional area of flow/wetted perimeter),
• S is the slope of the energy grade line, dimensionless (S = head loss/pipe length = hL/L).

As an equation for water flow rate for a pipe that is circular, the hydraulic radius is R = A/P = (πD²/4)/(πD) = D/4 and Q = VA = V(πD²/4). Substituting these equations into those for flow rate results in the following for the Hazen Williams equation in S.I. units:

$$Q=0.278C\times D^{2.63}\times S^{0.54}$$

(9)

• Q is the water flow rate in the pipe, m³/s.
• D is the pipe diameter, m.
• C is the Hazen Williams coefficient, dimensionless (depends on pipe material and age).
• S is the slope of the energy grade line, dimensionless (S = head loss/pipe length = hL/L).

The stream slope for the discovered water supply was estimated at 0.006 from field measurements, and the Hazen Williams coefficient for clay pipes is about 100.

According to Equation (9), the flow rate in a pipe with a diameter of 33 cm is

$$Q=0.278\times 100\times {0.33}^{2.63}\times {0.006}^{0.54}=95\mathrm{L}/\mathrm{s}$$

Also, the flow rate for the 40 cm diameter pipes is

$$Q=0.278\times 100\times {0.4}^{2.63}\times {0.006}^{0.54}=157\mathrm{L}/\mathrm{s}$$

Figure 11 was prepared using equations $Q=0.278C\times D^{2.63}\times S^{0.54}$ (S.I.) and $Q=0.000003763\times C\times D^{2.63}\times {({\displaystyle \frac{∆P}{L}})}^{0.54}$, with units as given above, to calculate the water flow rates for clay pipe with diameters from 1/2 inch to 6 inches (1 mm to 30 mm) and length from 5 ft to 100 ft (12 m to 150 m), all for a pressure difference of 20 psi (140 kN/m²) across the particular length of pipe. The Hazen Williams coefficient for clay pipe was taken to be 100.

The estimated water requirement for the old part of Boroujerd, home to 40,000 people, is as follows:

• Per capita household consumption was selected based on

  Table 1. Actual values of per capita household consumption (without landscape, livestock, and poultry) by population [36].

  Per Capita Consumption (L/Person/Day)	Population (Thousand)
  90–75	Villages
  110–75	Cities less than 20
  130–100	20–100
  140–120	100–500
  150–130	>500

  , which corresponds to a population range of 20,000 to 100,000. The estimate is based on actual consumption, with per capita usage evaluated at 130 L per person per day.
• Total amount of daily water consumption is

  (130 × 40,000)/(24 × 3600) = 60 L/s

The estimated water supply for Boroujerd’s historical district indicates that the east–west pipeline delivers 76 to 97 L/s, while the north–south pipeline provides 112 to 163 L/s. At half the north–south pipe’s flow rate, this supply meets the drinking and household needs of approximately 40,000 people, based on a daily water consumption of 60 L/s. This estimated water amount exceeds the consumption needs of the government citadel.

Due to the absence of data on Iranian society’s water needs 200 years ago, recent data was used. The available data includes a higher per capita water consumption rate, accounting for increased needs over time; therefore, the goal of design and structure of this water supply system can be more reliably understood. Consequently, applying current water needs to the context of 200 years ago, the system could have supported 40,000 people, indicating its construction served public benefit purposes rather than solely military ones.

Considering jars as dividers, inflow and outflow must obey the continuity equation.

$${\mathrm{Q}}_1=Q_2+Q_3$$

$$V_1\times A_1={\mathrm{A}}_2{V}_2+{\mathrm{A}}_3{V}_3$$

$$76{\displaystyle \frac{\mathrm{L}}{\mathrm{s}}}=38{\displaystyle \frac{\mathrm{L}}{\mathrm{s}}}+38{\displaystyle \frac{\mathrm{L}}{\mathrm{s}}}$$

After entering the jar, the 33 cm east–west inlet flow divides equally into 33 cm east–west and north–south branches.

According to the continuity equation, an input flow of 76 L per second into the east–west pipe is divided into two 38 L branches to supply different parts of the city.

The east–west pipe’s flow rate, calculated as 95 L/s (Manning) or 97 L/s (Hazen–Williams), splits at a divider into two branches of 47.5 L/s (Manning) and 48.5 L/s (Hazen–Williams). These branches likely supplied water to the east–west and north–south sections of the city, providing a simple method for water distribution. Without the divider, simultaneous distribution of water in both north–south and east–west directions would not have been possible.

6. Discussion

Historically, clay pipes offered a simple yet effective water transport solution, manufactured with environmentally suitable technology.

• The length of the clay pipes was four times wider than the diameter. Large clay pipe size indicated high-quality soil, resulting in more durable lines. The narrow head of the clay pipe was thinner than the broad head. It was a straight pipe made of pure, sand-free sweet clay, and well cooked. Clean clay, with sand and gravel removed through water, was more resistant [29,41]. Water flowed from the wider end to the narrower end of each clay pipe. The narrow end was coated with a two-finger-thick layer of lime paste, then inserted into the wider end of the preceding pipe and sealed.
• After the installation, the clay pipes were left for at least three days. Then, the water was allowed to enter them gradually. Applying melted tallow or oil to the clay pipe before installation increased its longevity. Clay was used to fill the area around junctions completely [29].
  Karji (a 10th-century Persian mathematician and engineer) offered technical basics on the installation of the clay pipe as follows:
  Maintain a 1:4 ratio between the clay pipe’s inside diameter and its length.
  Leveling the piping floor and installing clay pipes is a logical step.
• Accumulated air may exacerbate the effects of water hammer. Inadequate ventilation can trap air at high points, and it can create surges of pressure that damage pipes. Ventilation was employed every one-hundred cubits (45.7 m) to avoid air blockages and crushing of the clay pipes.

To seal the clay pipes against water leakage, Karji suggests impregnating the lines with melted tallow or oil. The pipes are then coated internally with bitumen or cement to prevent rust.

Ensure that the installation site for the clay pipe is free of any elevation changes. To stabilize the installation area for the clay pipe, pave the floor with bricks and lime [8]. The production process includes cooking limestone, combining it with water, and then adding 1 kg of olive oil to 12 kg of hydrated limestone. The prepared mixture is transferred into a large stone mortar and beaten with a wooden handle. It is essential to use freshly kneaded lime to prevent drying and deterioration. To extend the lime mixture’s shelf life, additional oil and vinegar can be added [32].

In Boroujerd’s historical districts, jars are located less than 47.5 m apart, and clay pipes have a diameter-to-length ratio of less than 1:4 (the size of the clay pipe is 34 cm, and its diameter is 31 cm). This difference arises from the type of soil used for the pipes, which has lower resistance than usual. Changing the ratio of diameter to length protected the clay pipes from breaking.

The lime mortar is used for connecting and sealing the clay pipes. Lime mortar is ideal for constructing stone and brick walls in water buildings. Clean-washed sand with lentil-sized grains was selected for the mortar, and the lime powder was turned into a paste. Lime sand was added gradually to the lime paste. This mortar was significantly stronger than modern cement. Some clay was added to the mortar to improve adhesion.

7. Conclusions

The discovered water system features storage jars spaced less than 50 m apart and clay pipes with a diameter-to-length ratio of less than 1:4. This deviation from standard proportions may be a result of using weak soil in pipe construction or the need to withstand excessive surface loads. The reduced ratio was likely a structural adaptation to prevent pipe breakage. The clay pipes were sealed using lime mortar made from clean, lentil-sized sand grains, ensuring a secure and watertight connection.

The system’s capacity exceeded the needs of both the government citadel and a population of approximately 40,000, indicating it served broader urban demands. During the Qajar period, Boroujerd’s water supply was sourced from the Haj-Gholam Ali aqueduct, Cheshmeh Malek spring, and several city reservoirs. The jars likely functioned as flow dividers, ventilators, and sediment collectors—similar in function to aerated wells—removing mud and sand from the water. Comparable clay pipe systems existed in other Qajar-era cities, such as Abbasabad Behshahr. The use of clay pipes for water transport dates back to pre-Islamic times, warranting further archeological investigation.