The abutments of what archeologists regard as probably one of the oldest dams in the world still survive in the normally dry valley of the Wadi el-Garawi forty km south of Cairo. The dam was built around 2700 – 2600 BC straight across wadi Al-Garawi, at a point where the valley narrows to about 100 metres wide.
The floor was covered with gravel and boulders of various sizes. The German archaeologist G. Schweinfurth, who discovered the dam in 1885 calculated that it had been necessary to excavate and transport approximately 100,000 m3 of rock and rubble for its construction.
The dam was originally 113m long and 14m high, but now there are only the remains of construction on both sides of the wadi. The northern wall extends about 24m into the wadi, and the southern one is about 27m long. Between the two preserved walls is a breach, circa 50-60m wide, which has been formed by the numerous floods of the past 4,500 years.
What are its structural elements?
In cross-section, the Sadd el-Kafara dam consists of three construction elements, of total width 98 m, which differ in composition and function:
- A central core of rubble, gravel and weathered material:
The central, impervious core of the dam is essentially calcareous silty sand and gravel. As this core material was mostly brought from the wadi terraces, it can be assumed that the filling progressed from the terrace edges toward the middle of the wadi.
- Two sections of rock fill on either side (upstream and downstream) of the core:
On both the upstream and downstream sides, the core is faced by sections of rock fill which support and protect it. The fill consists of rocks, usually 30cm thick, but these also range in thickness (10-60cm). The color and the mineralogical composition of these rocks show that they were quarried from the wadi banks in the vicinity of the dam. The quarried fill material was thrown down haphazardly and the cavities between these rocks were not filled with gravel or debris.
- The facing of the rock fill made of layers of blocks / ashlars placed in steps on the slopes of the rock fill:
The layers of ashlars (outside facing of the rock fill) are remarkable features of the dam. On the upstream side, parts of the facing are still well preserved. On the downstream side, isolated stone blocks indicate that facing corresponding to that on the upstream side was planned and at least partially constructed.
On the upstream side of the southern wall, only thirteen (13) courses of stone near the crest are still partially preserved. The facing of the upstream side of the northern wall is much better preserved, with thirty-one (31) courses still in place.
The ashlars are of slightly differing sizes (30x45x80cm, and 300 kg each on average), and were quarried from the wadi slopes. The coarsely hewn blocks are placed flat, forming terraced steps 30 cm in height. While the downstream face has a slope of 30°, the northern remains of the dam on the upstream side clearly show different slope angles: 43-45° in the lower section and 35° in the middle section. The shallow slope of the upper steps, circa 25°, may have been the result of much erosion.
There are no traces of operational devices such as outlets or a spillway. If they existed at all, which is doubtful, they would have been placed in the destroyed center portion of the dam. In any case, it appears that a spillway was not required. The way the dam was constructed it had a safe “spillway capacity” that could withstand the “force” of the reasonably expected floods.
A sag in the structure must have existed along the top of the dam that diminished the effective height of the dam. No mortar was used in the dam: ancient Egyptians did not use mortar as a cementing material.
Modern assessments of the dam’s stability lead to the conclusion that the design was basically correct, though conservative. This probably indicates that no experience with structures of this kind was available when it was built (Old Kingdom Era).
Considering the construction methods and technology available at that time, and taking into account the volume of gravel and rock fill that had to be transported from the wadi terrace to the dam’s core and facing, the construction can be estimated to have taken 10-12 years.
The total volume of the reservoir when fully impounded to an elevation of 125 m is circa 620,000m3. Below an elevation of 123.5m, about 465,000 m3 could be stored.
Why was the dam constructed?
Such a large-scale reservoir may have been needed either to fulfill a heavy demand, such as for irrigation, or to protect the downstream area from flooding. It is unlikely, however, that the Sadd el-Kafara dam was meant to supply water for irrigation and/or drinking: On one hand it is too distant from the alabaster quarries situated upstream to have supplied the labor force with water, and on the other hand, there is no evidence of cultivated land around the dam. Also, the absence of spillways in the dam indicates that the reservoir was not built for irrigation.
Due to the geographical and geological conditions prevailing in the catchment area of the Wadi Garawi sudden and heavy rainfalls lead to flash floods with disastrous effects in narrow valleys. Even nowadays inhabitants in the region have reported the recent occurrence of floods several meters high which have destroyed villages and claimed lives. It is assumed by many authors that the dam was intended for the retention of the rare but violent floods in the valley of wadi el Garawi. However, as there is no evidence of important settlement in the area, other authors wonder, what was it protecting?
In other words the purpose of the dam is still controversial. The prevailing opinion seems to be that the Sadd el-Kafara dam was built to protect the lower Wadi Garawi from floods and to protect the stretch of the Nile Valley at the mouth of the wadi where settlements were probably located.
The oldest dam in the world…
Since the rediscovery of the Sadd el-Kafara by Georg Schweinfurth in 1885, there has been no doubt that the dam is a very old structure. Analyses of pottery and radiocarbon dates obtained from samples of charcoal and textiles found in the remains of buildings northwest of the dam (probably a workers’ camp during the dam construction) indicate that the dam was constructed in the early Old Kingdom, circa 2,700-2,600 BC. This dating makes the Sadd el-Kafara dam one of the oldest in the world, and certainly the world’s oldest large-scale dam whose remains still stand today.
An uncompleted hydraulic work…
In all probability the Sadd el-Kafara dam was never completed, as there are no signs of siltation in the reservoir. There is evidence that the upstream rock fill was almost (or fully) completed, but a gap still remained in the middle section of the downstream rock fill, and perhaps also in the core, when the flood occurred. The inadequately protected core could not withstand the gush of the water overtopping it and was carried away causing the central part of the dam to collapse.
The collapse of the dam probably caused a catastrophic flood in the lower wadi. The impression left by the disaster must have been so terrible that the damaged structure was abandoned. The Sadd el-Kafara failure probably discouraged the early Egyptians from constructing other dams of the same composite section.