starting at the source Ain et Turab; here already start the inconsistencies.

Whereas in the first maps of the European travelers, as well as in their literature, the source springs much farther east and thus Wadi-upwards (G. Schumacher speaks of 550 m asl), today’s spring tapping which can be located at least since 1940 at a height of 439m asl can be found at least 800m away from it. Whether the todays source known by a Qanat of unknown length on the road "Ain et Turab" is actually the original one, or already a part of the 2nd aqueduct could not be clarified - even after multiple inspections and searches.
Sure, the spring pouring was sufficient and was demonstrably used to supply the Hellenistic settlement of Gadara until the Qanat Fir'aun was constrcuted. It is assumed that over the entire length or possibly only at some sections the water in the tunnel was conducted inside the pipes.
Here follows the second problem of this aqueduct connection, also called Qanat Turab. Due to the difficult topography and the height difference of 86.4m over a length of ~ 26.5km, several construction shafts were needed. In the Wadi Ain et Turab, or its lower course the Wadi Samar up to Gadara two tunnel systems can be found which cannot be clearly distinguished from each other in time.
After finding a second tunnel system under Gadara, a mistake crept into the literature, which always spoke of 2 m height difference of the tunnels to each other. Since the second, supposedly lying higher, tunnel system in Gadara was demonstrably built after the 1st one and remained apparently unfinished, all following scientists and archaeologists followed this assumption; even for the so-called overland aqueduct area. The upper aqueduct tunnel, which lies up to 40m higher in the upper wadi area than the lower one, was thus made the "Unfinished One" or the "Construction Error".
On the basis of summarized and provable facts, I would like to discuss the correctness of this interpretation, which is also mentioned in the book by M. Döring.
Previously, here is a section of the longitudinal section, also from this, the viewer may already recognize whether the section to the right of the red line fits to the upper or lower section

• The difference in height at the transfer point bridge (or even bridges) in Gadara is demonstrably almost the same for both city tunnels and cannot be used as justification.
• The more plausible longitudinal section results from the connection of the upper aqueduct route between Ain Et Turab and the destination point at the end of the bridge in Gadara.
  The result of it is an averaged gradient of 3.3 ‰, a maximum of 2% to max. 1km in length and a minimum measured slope of 1.48 ‰ shortly before Umm Qeis.
• By connecting the source with the lower aqueduct and the continuation up to the same point in Gadara, the following results:
  averaged gradient 3.0 ‰ (longer distance ~ 29.3km), maximum gradient > 3.4 PERCENT and minimum slope of 0.126 per thousand on long distance (several high accuracy points of 9.63km)
• why should the old Hellenistic aqueduct undermine the valley bottom in the area of the wadi-crossing? This can’t be justified by necessities (a side change Wadi-upwards would have been completely problem-free) and also brings increased problems in the drainage (sealing against surface water) and difficult construction conditions. Exactly this undercutting can be found at the lower tunnel!

here, an interim conclusion: The "new use" of the lower tunnel section proposed by M.Döring (Wadi crossing Section) through the new aqueduct coming from Syria, is not plausible!
The lowering of the old hellenistic course "without any pressing necessity" on the first 900m below the source of Ain et Turab by 3.4% results at much more difficult conditions through the embedding in and under the Wadi bed.
This subsequently also presuppose that, even in the Hellenistic period, the Qanat Course (without any pressing necessity) run on a route which could not have been built at that time. The Gradient of the following Section of the lower Aqueduct (Qanat) shows us, regardless of the type of construction (gravity-flow or carried in a pipe), that there is no hellenistic aqueduct worldwide with such a shallow gradient of only 12.5 cm per km. (Hints are welcome)
Even in Wadi Et Turab / Samar, there are tunnel heights of 70 cm to 4 m, flow widths of 40 cm to 1.2 m and narrow open sections opposite Samar, which thereafter interchanges by tunnel sections with a much larger dimension. See also the Subsite of Wadi et Turab.

But there are other important facts:

• The Qanat Fir'aun (from Syria), like the lower tunnel, has a very small gradient of 0.17 ‰ or below over several sections and over an uninterrupted length of 19 km. Similar lengths we know from the lower tunnel even under 0.11 ‰. This is a precision that could only be achieved by multiple measurements and with high-precision equipment in the Time after Christ .
• The engineering masterpiece of the Qanat Fir'aun comprises its planning from the outset and that the engineers has planed the integration of almost every source along the route. This only applies to the route section of the Qanat Fir'aun up to the reaching of the Wadi et Turab, as well as only to the lower tunnel with at least 7 recorded sources and their integraion. However,the upper tunnel does not integrate a single source. Why should the roman engineers change there tactics, which were proved so far?
• It is generally believed that the old Hellenistic course led the water over an internal pipe. But with constantly changing, albeit low, inflow of at least 7 additional sources, the pipe dimensions would have to be adjusted as well. At least there should be transfer tanks, as small reservoirs, at each of the sources. All this has never been found or described anywhere. Why then should have been chosen this much more difficult and longer route for the Hellenistic period of use?
• Another important fact is, at least "one",construction shaft exist upstreams of the crossing point of the Qanat Fir'aun with the old Aqueduct Line, described by S. Kerner and the University of Karlsruhe, as well as by the project team of the Qanat Fir'aun found and calibrated, on the south side of the Wadi.
  -The striking wadi crossing had been built also in the already described construction type, by means of an artificially sill constructed after a natural vertical drop.
  The construction shaft, with a rectangular winding staircase of 180 degrees, was built like as often in the course of the Qanat Fir'aun slightly off-centered of the wadi's flow channel and appears in design and connection to the tunnel of the same age. As in the further course, no inlet or outflows in the tunnel indicate that this tunnel section on the south side of the Wadi slope had an inlet from the Ain et Turab, M. Doering concluded that the Wadi-crossing originally belonged to the lower hellenistic route. However, the above mentioned construction shaft ,discovered by several project groups, proves that there must have been an aqueduct line to Ain et Turab on the south side and this may have been connected only to the original upper line. Thus, as the older aqueduct, only the upper tunnel system comes into question.Against this thesis put forward by me and for the consistent planning of Qanat Fir'aun and thus also the lower tunnel to Gadara, there is no evidence to my knowledge. But I hereby like to put it up for discussion.

The question then arises whether the dropped upper tunnel in Wadi Ain et Turab, which in addition was built on the entire length to Gadara and in verifiably many construction lots, was actually only a never-used "building defect or construction error"?
As it can be seen from the facts summarized above, the upper tunnel without additional intermediate feeds with a slightly higher but steadier gradient is the more plausible solution for the Hellenistic period - precisely because a plaster was still found in a few areas.
The fact is, the upper tunnel has been abandoned in a construction phase! Almost over the entire length, contrary to the other practices, the construction shafts are unlocked and "marked" by building rubble lying in front of them.
The solution can be found in the described section of this tunnel in the Ibdar area, which is also often described as the "chaotic tunnel", from the pilot-tunnel "widened" and ascending “contrary to the direction of flow”. In my estimation, the upper Qanattunnel was actually used for Gadara’s supply in the Hellenistic period or for the construction of the Qanat Fir'aun. (whether with or without pipe guide is not clarified here ;-)) Then it was tried to extend the existing cross-section, which was probably originally much smaller, and to adjust the slope of the new incoming Qanat Fir'aun route. The existing gradient was reduced and created up to 5m high two-story cross sections. By comparing the data, however, it was noticeable that the incoming new Qanat Fir'aun could not match the maximum feasible changes of the old upper route due to the already very small incline and the necessary alignment. At this time, the old Qanattunnel was completely abandoned and reused only shortly before Gadara, a long time later.
However, even after the mountain tunnel "Dahr Defur" in Wadi Ain et Turab, the alignment and the routing properties continued to be complied with and implemented. Both the inclusion of the source and the gradients thus obtained a consistent engineering image.

Here you will find the link to the end of the Qanat Fir'aun at the bridges in front of Gadara.

In addition, I would like to reiterate here that I wish a constructive criticism of this thesis and would also like to provide the correct surveying results of the project etc. The datas used by M.Döring in the book "Wasser für die Dekapolis" and the values which were "adjusted" by the actual measured heights of up to 4.50 m are thus demonstrably non-existent. These alternative facts for the determination of the gradients in the book, rather served there in order to let flow the water in the sense of the "intended theses".

Here you can see the exact geolocation of this aqueduct section.