SearchResearch Challenge (7/25/18): The Mystery of the Salzburg Stream--does it flow uphill?

I've been in Salzburg, Austria
for the past week... 

It's just as lovely as you might imagine--the Alps surround a large river valley, it's endlessly green, and the Altstadt ("old town") is full of medieval streets, lined with churches and shops that have been around for hundreds of years.  And yes, the hills are alive with the sound of music--at least I went to enough concerts to convince me of this.  

The surrounding area has a web of bike/foot paths and streams that seem to run every possible way.  They're lovely, but it's a little confusing when you first arrive, although you learn the paths quickly.  That's when you start to notice the little things--the things that make you say "What?"  

My first big surprise (after I got to know the place a bit) was the peculiar behavior of a stream that I passed often on my walks.  As I walked to the foot of a pathway that climbed up to the castle wall, I had to pass over a small stream.  It was a beautifully flowing stream, just about the platonic ideal of a stream. 

One time while I walked this path I paused for a moment, looking down at the water and noticed that it was flowing from south to north.  That was so unexpected that I dropped a leaf into the water to verify that what I thought I was seeing was actually what was happening.  Why was it so unexpected?  

It looks like the water is flowing uphill!  What?  

The little bridge I was standing on is clearly downhill from the where the stream starts.  It looks for all the world like the stream is running up the hill towards the castle!  

Here's the place (from Google Maps, in 3D mode).  In reality, it's clear that the left part of the picture is uphill from the right part.  

The white building at the top of the image is the old city castle, the Festung Hohensalzburg (that is, the "high Salzburg fortress").  It sits atop the Festungsberg, a hill that rises up over the historic center of town.

Just below the fortress is a patch of forest, and below that is a meadow.  In the middle of the meadow is a stream that ends in a clump of trees and brush.  

Actually, that's what I noticed the first time I walked past--this looks like the source of the stream, the spring from which the stream flows.  As I passed I thought to myself, "Oh, there's a spring, the source of one of the many brooks..."  (Since I grew up in LA, I've always thought of springs as being somehow magical.  I never saw one until I was in my mid-20s, so I notice them.)  

Here's the map of that place.  See the blue line of the stream?  That dotted line is the pathway where I'd walk into the Altstadt.  This all makes sense--it follows exactly parallel to the path, and you can see the little bridge on Brunnhausgasse where I crossed it.  The map suggests that this is the spring source.  

Here's the same scene in the satellite view.   It sure looks like the source of a spring.  

As I walked past, I took a quick photo, just so I'd remember this for SRS. 

Location: https://www.google.com/maps/@47.7945965,13.0444718,18.33z 

But... as you see in this map, the water is flowing from south to north!  How is that possible?  The slope of the hill is increasing from south to north.  

This leads me to this week's SearchResearch Challenge.

How is it that this stream in Salzburg is apparently flowing uphill?  What's the real story behind this gentling flowing brook? How is this possible?  

Once you figure it out, be sure to let us know WHAT you did to come to this understanding.  (I have to admit I was rather surprised when I discovered the answer.) 

Hope you enjoy this Challenge!  


Search on!