Before the Dams

I have always loved the juxtaposition of a modern subject with its historical counterpart: comparing old street scenes and architecture in a city to present-day (see the great  Before and After NYC  image-swipe collection by Paul Sahner), a rich time-series of land use change represented in aerial photography, or the evolution of a someone's portrait over many decades. These are the individual pages in the Living Atlas of human existence. (sorry)

This story looks at the changes humans have made to the landscape through the diversion of surface water, specifically, through the creation of dams and reservoirs. To do this, we'll use photographs of dams taken before or during their construction, then compare these waterways to their present state in 3D using ArcGIS Pro and trickery. We'll focus on three dams which were constructed in the early- and mid-20th century, and use best-available hydrographic data to represent the participating rivers and reservoirs in a scene with these dams:

• O'Shaughnessy Dam
• Grand Coulee Dam
• San Luis Dam

Next comes the hard part: attempt to recreate the viewing perspective of the historical photographer who captured these reservoirs before they were filled, so that we can compare the relatively pristine river valleys of the past to their present-day water bodies.

The historical images:

My initial story idea wasn't centered around old photographs. I originally wanted to virtually drain each reservoir in 3D by finding bathymetric (underwater terrain) data, then visualize different water levels and explore the hidden features below - a topic prompted by recent years of California drought, followed by extreme precipitation and reservoir-filling during the winter of 2022/2023. When I totally struck out finding any bathymetry data for the reservoirs I was interested in, I started looking for historical pre-dam construction photographs as a backup plan - and ended up with an entirely different story. I needed to recreate these pre-dam photograph locations virtually, in 3D.

If you've ever played the online location-based game, GeoGuessr, where you are dropped into an unknown Google Street View location and have to navigate the street network looking for signs and landmarks - and a precise pin placement for maximum points - it's a similar thought process: look for very local context clues, find where the foreground and background objects intersect, and keep exploring (in 3D) until you get close to aligning the terrain and features from the photograph. (And eventually, give up and settle on something that's close enough.)

With the photographs selected, I just needed detailed surface water data to add to the "present day" scene views.

The  National Hydrography Dataset Plus High Resolution  is the  Most Detailed Map of US Waters That You've Ever Seen . As far as authoritative hydrographic datasets are concerned, this is it: 25 million rivers, streams, pipelines, and other linear features, over 7 million lakes, ponds, reservoirs, wetlands, and other area features.

In addition to its rich attributes and beautiful cartography, NHDPlus is also a great resource for use in 3D - many of the lakes and reservoirs contain elevation attributes - and when combined with dynamic water effects and reflections in ArcGIS Pro and ArcGIS Online, you can make some pretty compelling visualizations.

Let's dive in and start building some dam scenes.

The O'Shaughnessy Dam began construction in 1919 and was completed on July 7, 1923, forming what we now know as the Hetch Hetchy Reservoir. The 1906 San Francisco Earthquake prompted an urgent need for a safe and reliable source of drinking water, and the Hetch Hetchy Aqueduct system has met that need for the past 100 years. Providing water for over 2.4 million Bay Area residents, it is gravity-fed through aqueducts and pipelines over a distance of 260 miles. In addition, the Hetch Hetchy Power System, which is comprised of Hetch Hetchy Reservoir, Lake Eleanor, and Cherry Lake to the west, generates some 385MW of hydroelectric power.

For all of the dam examples in this story, I first added the NHDPlus service to a new scene in ArcGIS Pro, using the Imagery Basemap. Next, I applied a definition query to the area features using the gnis_name attribute: "Hetch Hetchy Reservoir", and set the polygon to display at an Absolute Height, using the reservoir polygon's elevation attribute of 1,157.3 meters (3,797 feet).

The dynamic water effects are the finishing touch, adding waves, reflections, and ambiance. To enable these in Pro, open the Format Polygon Symbol options for the reservoir polygon and change the fill type from Solid to Animated and the Waterbody size and Wave strength to your liking. The lower wave strength options wear small, especially from higher camera viewpoints, so I tend to use the biggest option. Finally, I added a wave direction of 245° so the waves move towards the dam.

Once the scene was ready, I put the old photograph on a second monitor and moved the camera around in the Pro scene until the background and foreground features came into alignment. Like georeferencing a raster image on a 2D map, I used two mental "control points" above the water line where terrain was visible: the V-shape created by the overlap of the foreground and background mountains on the right, and the saddle feature above the waterfall in the center. These locations helped to constrain the number of possible 3D perspectives while still standing on the ground.

You always get lucky the first time, which I realized after aligning the next two dam photos. I exported 3 animation images of Hetch Hetchy (single PNG frames) at slightly different elevations and perspectives and the third one was a pretty good match. Ship it!

Photo Match Attempts: 3

The Grand Coulee Dam, on the Columbia River in Washington state, was constructed between 1933 to 1942 to supply hydroelectric power and provide irrigation water to 671,000 nearby acres of agricultural land. During World War II, the electricity was also used to assist the war effort in the smelting of aluminum for aircraft and equipment, but also to produce plutonium for the top-secret Manhattan Project at the Hanford Site in Richland, Washington, to the south.

The Grand Coulee Dam produces 6,809MW of electricity from three power houses, making it the largest power station in the United States - and dwarfing the Hetch Hetchy Power System's paltry 385MW.

Due to the scale of the project, there were many challenges in its construction - few companies were equipped to even take on a project of this magnitude. Eventually, the first stake was driven in, in 1933, and President Franklin D. Roosevelt visited the site a year later, encouraged that the project fit nicely into his New Deal with the Public Works Administration. Worried about the private ownership of utility companies and price-gouging, a Supreme Court decision gave the green light to federal ownership of the land and dam (still under construction) in 1935.

"I leave here today with the feeling that this work is well undertaken; that we are going ahead with a useful project, and we are going to see it through for the benefit of our country." -- President Franklin D. Roosevelt

Matching the pre-Grand Coulee Dam picture of 1942 in Pro upped the difficulty quite a bit compared to the ground-based Hetch Hetchy example. It's an aerial photograph, which introduces an unknown altitude, and as I was to discover, a slight roll, which you can see in the skewed black border on the right swipe image. This means figuring out the full gamut of position information in 3D: X, Y, Z, Heading, Pitch, and Roll.

I'd now like to draw your attention to the top third and right halves of the swipe, near the cliffs and crescent-shaped lake, because that's where the match is pretty good. It was more difficult to maintain alignment simultaneously on both sides of the Grand Coulee photograph, which I chalked up to image distortion and I also ran out of ideas.

Photo Match Attempts: 8

The San Luis Dam is a bit different from Hetch Hetchy or Grand Coulee: the off-stream reservoir is not located on what was previously a riverbed, but acts as a giant bathtub that water is transported to for storage via pipelines and aqueducts from other California rivers - most is pumped uphill from the San Joaquin-Sacramento River Delta. It also happens to be the largest off-stream reservoir and the largest embankment dam in the United States, holding 2,041,000 acre-feet of water at capacity. Hydroelectric output is a Hetch Hetchy-like 424MW.

Unlike the previous two examples, the San Luis photograph was taken prior to the dam's completion in 1967, but before the water was piped in. This offers an interesting glimpse at the finished internal structure of a dam, with the four prominent intake towers now mostly hidden by water. A little transparency applied to the NHDPlus water surface also lets the imagery below show through, revealing more details about the near-shore topography and local highs that would otherwise be obscured.

The key features for aligning the photo with the scene were: Highway 152 trailing off into the background on the right, the dam's diagonal earthen wall extending towards the highway, and the white water intake tower structures. Like with the previous Grand Coulee aerial photograph, getting the elevation right was an additional challenge in matching perspectives. Despite the obvious linear control features, this one was beguilingly difficult.

Photo Match Attempts: 11

The removal of dams in the United States and across the world has picked up pace in recent decades, a decision driven by several factors. The loss of biodiversity and protection of native species, such as anadromous fish who rely on unrestricted travel between the ocean and fresh waterways for spawning, have outweighed the benefits of hydroelectric power generation and fresh water storage and delivery in many areas. In other cases, the structural integrity of old dams and the risk of failure is the primary driver in their dismantling.

With the largest dam removal project in history beginning in late 2023 on the Klamath River in Oregon, reclamation is an active topic for exploration and discovery. How will these newly-unrestricted waterways find their courses again, and what can we learn by looking to the past?

Do you live near a dam? Do you like 3D? Do you drink water? If you answered "yes" to any of these questions, I encourage you to explore the new, amazing, incredibly detailed National Hydrography Dataset Plus High Resolution maps in the ArcGIS Living Atlas of the World, and have fun exploring and discovering!