After a visit to the Sumas Valley in north Whatcom County, I headed south via Telegraph Road, Sorenson Road and Goodwin Road. Lots swampy ground is present along the Sorenson and the north end of Goodwin. Water was pouring over Goodwin Road.
Road erosion at the head of the spill over is thus far minor
The water is from Breckenridge Creek. The creek is having a hard time passing all of its water under Goodwin Road and my general sense looking into the brush is that the stream may be going through a bit of a channel change upstream. The problem for the creek, and the Public Works folks, is that the gradients in this area are very low and the creek is flowing onto a landform area not of its own making.
Breckenridge Creek is flowing into an area of large glacial river outwash channels and late ice age moraines associated with what has been termed the Sumas Stade. That is the ice front lingered in the Sumas area leaving behind a landscape that has very little to do with the current streams.
DEM of part of the west edge of the Sumas Valley
Moraine features are evident north of the Kinney Creek label
Note also that the glacial outwash contains several gravel mines
In the DEM image above Kinney Creek and Breckenridge Creek flow off the north slopes of Sumas Mountain and encounter an old glacial outwash channel that flowed out of the ice front, the moraine of that ice front can be seen just north of the Kinney Creek label. Kinney Creek has somehow managed to flow north opposite the former outwash flow path. Brekenridge Creek flows west across the old channel then flows southwest along the base of an elevated area of outwash before turning west and joining the Sumas River. The west path of Brekenridge is intriguing in that it makes a narrow cut through a ridge of elevated glacial sediment. Just how that happened would be a rather difficult exercise that requires pulling back further and thinking through a lot of factors. And for that matter, Why is there such a narrow ridge of glacial sediment at that location?
The main take-a-way is that this is an area where the existing streams are flowing across a landscape that was formed by other processes. It does not take much for these creeks to fill their channels and spill over and find new courses. Brenkenridge Creek is actively eroding its incised valley upstream of the low lands. That sediment load will readily fill its channel on the low lands. Breckenridge is not the only creek posing flooding problems in this area. Most of the streams entering the Sumas Valley pose flooding problems and many have long histories of sediment management issues. Any large change in sediment flux in these streams poses a big challenge (hint: look at the DEM at Swift Creek).