Building a Hippo Home

Brian Boecker
Brian Boecker of Mortenson Construction helped design the Dohmen Family Foundation Hippo Home.

When Brian Boecker was working on his very first construction job in high school, he probably never imagined that someday he'd be building a home for hippos. But in his role as project manager for Mortenson Construction, that's just what he has been doing. For much of 2009, Boecker worked with a team of designers, architects, and engineers to design and build a state-of-the-art hippopotamus enclosure for the Milwaukee County Zoo (Wisconsin).  

The enclosure, which is called the Dohmen Family Foundation Hippo Home, is a 1,500-square-foot extension to the north end of the Milwaukee County Zoo’s pachyderm building. It was designed so that a 5,500-pound male hippo named Happy could travel from the National Zoo in Washington, D.C., to join Milwaukee’s two female hippos, Patti and Puddles. Construction started in April 2009 and ended September 2009, in time for Happy’s Sept. 29 arrival. The new facility was made possible by a $1.75 million donation to the Zoological Society of Milwaukee from the Dohmen Family Foundation. The new hippo home is considered Phase 1 of what is hoped to be a two-phase project. Phase 2 would include an outdoor underwater viewing exhibit that could hold up to four hippos. (Zoological Society members: Click here for a story in your January 2010 Alive magazine on the new exhibit.)

"When you are building an exhibit for an animal [as opposed to a structure for humans], the biggest difference is that everything is heavy-duty. Everything is super-sized," says Boecker. This is especially true when working with hippos since they are the second largest land animal on the planet (elephants are the largest). On average, female hippos weigh up to 3,000 pounds and male hippos can weigh up to 6,000 pounds. So you can imagine that animals this large are going to require heavy-duty enclosures with sturdy floors, extra-strong walls, and steel-reinforced gates. 

Ray Hren inspects the new hippo gates Viewing window glass
Pachyderm zookeeper Ray Hren shows how a heavy-duty, open-frame wall moves along a track to create a smaller space so veterinarians can get close to a hippo for a medical procedure. It took five layers of sturdy glass sealed together to create the viewing window (background) into Happy the hippo’s quarters.

Working with animals this big can be a dangerous job for zookeepers. So Boecker and his team designed the exhibit with zookeeper safety in mind. They placed three sets of mirrors near the ceiling of the new hippo enclosure to serve as an “extra set of eyes” for zookeepers. From the hallway, keepers can see Happy’s pool and both doors between the stalls before they open any gates. The new extension was designed so that, if all gates are opened, all three of the hippos can move freely in a large circle from the main pool to Happy’s pool extension to the new stalls to the hallway to older stalls and back to the main pool. Also, the public viewing window has five layers of glass between Happy and zoogoers.

These pipes carry temperate water into the hippo enclosure so that the pools stay at about 60 degrees.

How did the engineers figure out how strong those gates needed to be to protect humans from the hippos? It took lots of planning, says Boecker. For instance, to decide what kind of metal to use for the gates, they had to calculate factors such as how much hippos weigh (Happy is our biggest hippo at 5,500 pounds) and how fast they can run (up to 30 mph!). Then the designers calculated the largest hippo's momentum and the energy of impact if he were to ram up against the gate. In the end, they decided to go with 1/4-inch-thick galvanized steel for the gate. According to Boecker's calculations, this would be strong enough to control the hippo's movements but still light enough for the construction team to work with.

Hippo holding pool
Happy has his own pool that leads into the main hippo pool.

Another area that required a lot of planning and research was an 80,000-gallon pool that the Zoo hopes will be part of Phase 2. Boecker said Mortenson had to build the Phase 1 extension to be ready to connect to a potential outdoor pool. Happy’s pool contains pipework for a future filtering system. Right now, the water is cleaned through a dump-and-fill system. The water is dumped out, the pool cleaned, and the pool re-filled with tap water. But a future outdoor pool will have a water-filtration system. “My team and I had to think about the pool in terms of the hippos’ well-being as well as how to best create a great experience for Zoo visitors,” says Boecker. “We have some great people working on the water-filtration process, and they are planning to have the water crystal clear. This will be good for the hippos’ health as well as making it easy for visitors to look through the underwater window.”

The water will also be kept at a comfortable temperature for the hippos. The new water-filtration system will use special "heat exchangers" to keep the water at around 60 degrees throughout most of the year. Plans are also in the works to have the outdoor warm pool do double duty.  A Milwaukee-area non-profit urban agriculture organization called Growing Power would provide the Zoo with hundreds of young tilapia fish every spring. They would be raised in the hippo pool until they grew big, and then would be returned to Growing Power in the fall.  

Mirrors, gates, tilapia, heated water...who knew that there would be so many different factors to consider when building a hippo home?

Hippo Home Exterior
The exterior of the Dohmen Family Foundation Hippo Home is
surrounded by attractive landscaping and flowers.

Text by Brianne Schwantes. Photos by Richard Brodzeller/Zoological Society of Milwaukee