For those who focus on the details of flood events, here is a collection of data points from my travels around the Alewife and Mystic from Sunday into Tuesday. It is important now that we assemble observations from this event and learn as much as possible. Clarissa Rowe will be convening a meeting of the Arlington-Belmont-Cambridge Stormwater Flooding Board for that purpose. But I wanted to collect what I had here.
I will make one summary observation: It is consistent with the timeline below to believe (a) that the blockage at the Craddock Bridge helped elevate the crest on the Alewife Brook and (b) the blockage was perhaps responsible for taking it up the last few inches which led to the worst of the North Cambridge flooding. On the other hand, the fact that water only dropped 8 inches in the 8 hours after the removal of the dock suggests that the contribution of the dock was not overwhelming — the slope of the water level drop at the gauge on the Alewife did not change much as of the removal of the dock.
- On Sunday night, Alewife Brook Parkway was flooded but still passable at 6 on sunday night, according to Steve Kaiser. By 8PM when I came by, the parkway was closed, but water did not appear to be extended across the parkway.
- At 8PM on Sunday night, the gauge under the Broadway bridge was reading approximately 6 feet. The web telemetry was down, so that was just what I could make out in the dark.
- According to a Harrison Avenue resident (North Cambridge near the Alewife Brook), basement flooding on Sunday night was only ground water seepage and his pumps could keep up.
- Water began rising on Harrison Avenue early Monday morning, but with auxiliary pumps he was able to keep up.
- Water rising on Harrison avenue connected with water in his back yard toward the brook in the late afternoon on Monday and at that time, water began rising rapidly in his basement and overwhelmed his pumps
- At 5:00PM Monday, rainfall and Northeast winds were still very heavy.
- At 5:15PM on Monday, all three pumps at the Amelia Earhart dam were roaring away. The racket was impressive from hundreds of yards away. A flood control operator at the Charles pump station stated that all three pumps at both stations had been in operation since Friday night. Three thick plumes of diesel smoke from the Earhart dam confirmed the pump operation. The locks appeared closed at that time. The tide was low, but perhaps elevated by the winds.
- At 5:45PM on Monday, the Craddock bridge was occluded by large dock section approximately 25 feet in length and (visible only later) six feet in width. The section was almost entirely submerged and pressed broadside to the bridge by the current. The rightmost arch of the bridge was fully open but water was dropping approximately two feet as it swirled around the dock and through the bridge.
- Scuttlebut from workers at the bridge on Tuesday suggested that the dock lodged itself against the bridge sometime during the day on Monday.
- At 6:00PM on Monday, the gauge under the Broadway bridge was reading approximately 7.3 feet, suggesting in conjunction with the Harrison avenue observations that somewhere around the 7 foot mark is where North Cambridge neighborhoods really get soaked.
- At 6:30PM on Monday, Harrison Ave in North Cambridge was roughly one foot under water.
- At 8PM on Monday crews arriving at the Craddock bridge made an assessment that give the current pulling under the jammed dock, they lacked the equipment necessary to safely attempt a removal of the dock. DCR struggled into the evening to assemble the necessary bucket truck and crane.
- By 10PM on Monday, the rain seemed definitely to have stopped.
- At 10PM on Monday, the Sunnyside neighborhood had water up to the backs of the houses.
- At 6:30AM on Tuesday, the water level in Blair Pond was still above the top of the outfall pipes to the Wellington Brook, but the driveway to the high school was clear.
- At 6:45AM on Tuesday, the water level on the Alewife Brook was still at the 7.3 foot level although the water on the Mystic seemed to be dropping. (My recollection is not consistent with the telemetry which indicates something like 6.9 inches at at time.) Either way, it appears that the peak occurred at some point during Monday night. This hypothesis is consistent with the shape of the flow curve at the gauge (although that curve is interrupted by a telemetry loss). Comparison of that gauge to the Aberjona guage suggests that as Alewife stream velocity crested on Sunday and slowed dramatically as the crest came down from the Aberjona.
- At 7:00AM on Tuesday, the water had dropped a few inches to expose more of the dock jammed at the Craddock. The current, though still strong, seemed weaker.
- At 9:30AM on Tuesday, the first big piece of the jammed dock came out.
- Just after 10AM on Tuesday, DCR crews with the assistance of Medford firefighters and DOT equipment operators had successfully removed rest of the dock.
- At 10:30AM on Tuesday, the water level had dropped to 6.7 feet at the Broadway guage.
- At 10:45AM on Tuesday, Harrison was clear and basements were being pumped out.
- At 5:55PM on Tuesday, the water level in the Alewife Brook had receded to a little below 6 feet.
- At 6:00PM on Tuesday, the Alewife Brook Parkway was still blocked, but only by residual water which workers were pumping out.
- At 6:15PM on Tuesday, the water level in Blair Pond had dropped just below the top of the outfall pipes. There was no evidence of any obstruction in the immediate vicinity of the outfall pipes.
Your observations much appreciated as comments to this post. For policy thoughts, please comment at this link.