The proposal to develop the waterfront area — the old Alco site between Erie and the Mohawk — involves property that lies entirely on the 100-year floodplain. The entire site was flooded and underwater during Irene flooding in 2011.
If historical flooding can be our guide, the fact that it is on the 100-year floodplain means that there is a 1 percent probability of inundation every year. If, however, the frequency of flooding and extreme events is increasing, as many suspect, the site could see even more frequent flooding.
We need to be very careful about how we treat the floodplain on the Mohawk River.
River widening and river deepening are not effective methods of flood mitigation. Rivers don’t work that way. In big floods, no amount of channel change can affect the river level (flood stage). Sedimentation and infilling can, and do, occur very quickly on this part of the Mohawk.
Thankfully, scientists and planners at the state Department of Environmental Conservation are aware of how rivers work and why we shouldn’t block or impede flow on a river. They also know that unpermitted channel modification is illegal in the state of New York.
Development on the floodplain hinders the flow and movement of flood water and the availability of the floodplain during high-water events. We need to work to free our floodplains, not restrict them. If the floodplain is occupied, covered and built up, it means that all that water needs to go elsewhere.
Where does that water go?
The water will get backed up, and upriver areas will see higher levels in flood events. This would then have an impact on the Stockade, a historic and charming section of Schenectady that is already dealing with chronic flooding issues.
Let’s not make matters worse.
A major issue of concern on this section of the Mohawk is ice jamming and ice-jam floods in the winter and during spring break-up. We know that historically the majority of high-water events in Schenectady have been related to ice and jamming of ice downstream.
In 2007, an ice jam blocked the river and the river level rose about 15 feet in hours, flooding parts of the Stockade: Emergency management had only hours to coordinate and execute evacuation.
From a development standpoint, the issue of ice and ice jams means three things.
• Rapid flooding and inundation of the 100-year floodplain occur and are hard to predict.
• Ice needs to move freely through the river channel.
• Ice can be very damaging to open and exposed structures along the River.
When part of the built environment impinges on the channel, or when we cause irregularities in the channel, we create places for ice to get caught and for ice jams to occur. As recently as 2010, walls of a building were bashed in by large ice floes in Schenectady County.
If a hydrologic model was used to evaluate the effects of the development on River flow, it is unlikely that ice and ice jamming were part of that model because this sort of flood mechanism is so complicated it defies models.
We should not forget the flooding that occurred during Hurricane Irene in 2011. Too many people suffered property damage and personal loss in that terrible flood. Let’s think differently and work to keep the flood way clear so that the River can use it when it needs to.
This means we need to build resilient communities and we need to implement smart-growth strategies.
I am not anti-development. On the contrary, I’ve been delighted to see the deep and meaningful changes that have occurred in the city of Schenectady in the past 20 years. But given all the work and effort that has gone into understanding floods and flooding in Schenectady, it would be unwise to allow this development to add to our flood woes.
Instead we should look into plans to develop a green necklace along the waterfront, linked by paths and bikeways that connect with those in Glenville and Scotia.
In moving this project forward, let’s move the development back, away from the banks of the river. Develop the site, but keep structures away from the river bank.
A linked and integrated river-lining greenway could be woven into development plans in a thoughtful and meaningful way that could add value to the developed site and the community.
The proposed development could then take advantage of the intervening riverbank green space that would be more fully integrate into the fabric of the city.
Creating green space along the river could be an important economic engine that drives flood-smart growth.
John Garver is a professor of geology at Union College. The Gazette encourages readers to submit material on local issues for the Sunday Opinion section.