On January 10th, 2014, I accompanied a small group of scientists and wetlands advocates as they toured three heavily eroded sites on and around Bull Mountain. Brian Wegener of the Tualatin Riverkeepers has posted an excellent overview of the tour at https://tualatinwatch.blogspot.com/. All these sites are significant and were wonderful to see; but the mess in the ravine west of SW Essex Drive was particularly wonderful. I mean "wonderful" in the Oh-my-god-what's-happening-here? sense of the word.
The last time I trecked through this ravine was in the summer of 2009. That day I entered at the same access point we used on our tour - the place where Essex meets SW Lauren Lane. Then as now there was a barricade in place with a sign that identified the area as being part of the Tigard Greenway. But back then the "trail head" was simply a worn spot in the weeds and the ravine itself was considered unsafe for hiking, at least officially. The trails through it were not well constructed or even regularly maintained. At that time it was possible to spot places where the walls of the ravine were clearly on the move, but the complex of pipes that appear in both this post and Brian's were still a few years in the offing.
While major erosion was clearly taking place all along the walls of the ravine - particularly along the eastern wall, the Essex side - I don't recall seeing anything quite so extreme as what we saw on the 10th. What's happened, I wonder, to move the situation so far up the curve in the 4.5 year interval? My guess is that what we saw on the tour was merely the result of process-over-time. In all liklihood the foundations of the problem were laid when the homes were in the process of being sited and built. Where the movement of water through and over land is concerned, a great deal of change in landforms can take place in minutes and hours, much less in years! That's particularly the case when the ground itself is rotten ("rotten" in the mountaineering sense of the word) and the volume of water it is subjected to is substantial
In addition to issues with the integrity of the slope where the pipes are installed, a few hundred yards further along the rim to the north, the rear foundation of one home is clearly under attack by geological and hydrological forces that are working incessantly on the walls of the ravine. The ground in that area has been covered with a layer of heavy plastic, presmuably in an effort to slow down the process of erosion during the rainy season. I'm not privy to the facts of the case, but my guess is that it is at least serious, if not critical. The situation is similar to others that have taken place previously on Bull Mountain, particularly further to the east along Derry Dell Creek. But the gash that is home to Derry Dell is merely a crack in the ground when compared to the young and growing canyon that lies between SW Essex and SW Ascension Drives.
There are 60+ houses along the upper elevations of the ravine. They were built there in the mid-to-late 1990s, and the construction of each and every one of them was regulated by statutes and and/or standards estabished by the City of Tigard and Clean Water Services (CWS). The basic documents in force at the time would have included the City of Tigard's Municipal Code and Clean Water Services Design and Construction Standards. Over and above simply providing guidance and regulations aimed at insuring compliance with a wide variety of municipal, regional, state and federal strictures, these codes are intended to protect life and property. That being said, a couple of questions immediately spring to mind:
1. Presuming that the city and CWS enforced the permitting process properly, and presuming that the builders and their designers followed through on their ends of the deal by executing their projects in a proper and professional manner, why is at least one home along the rim of the canyon (and possibly more than one) now (apparently) in jeopardy?
2. Am I off base in thinking that (a) either something has changed in the fundamental conditions related to the area, or (b) some of the strictures and best practices in either or both the Tigard Code or CWS Design and Construction Standards weren't well enough grounded to prevent the problem from developing in the first place?
I think these are important questions for both Tigard and CWS to address because an ambitious develoment called "River Terrace" is being proposed by the city for an area of Bull Mountain just west of the the ravine that's been the focus of this post - an area that almost certainly has already played a part in the erosion on Mike Meyers that Brian talks about in the first segment of his post. Given previous incidents at Derry Dell and the current state of the ravine between Essex and Acension, it would be unfortunate if a new and major development were to take place on Bull Mountain before existing slide AND erosion concerns were fully and adequately readdressed.
Thanks in part to a technology known as LIDAR, the complex geology of Bull Mountain is more well understood than ever before. Also more well known than ever before is the dramatic interrelationship between that geology and the stormwater that visits it on an anual basis. What this means is that current scientific data is more than sufficient enough to help the city make smart and sustainable decisions about how it manages its stormwater management responsibilities.
Chapter 18.775 of Tigard's Municipal Code deals with the topic of "Sensitive Lands." The Municpal Code is reviewed from time to time, as it should be, to make sure it continues to meet the needs of the city and its citizens. Maybe it's time for another look? As I was reviewing the chapter this morning it struck me that while there are specific and detailed sections titled "General Provisions" for floodplains and wetlands, I couldn't find one that directly addresses areas with steep elevations and/or unstable topography - i.e., sensitive lands. For example, the code makes it clear that there should be no development on lands with slopes of more than 25%; but I couldn't find anything that is specific about how far back from the edge of a clearly rotten rim should the footings for a home be placed?
I'm not at all convinced the code effectively addresses the complex interrelationships that exist between the morphology (slope and soil features) and hydrology (wetlands and drainages) of given areas. Each set of variables appear to be set apart from the others and then addressed as if it were a free-standing or self-contained system. Maybe what is needed these days is coding that looks at the elements as groups of similar variables operatnig within the context of a more complex and diverse system?
Given that a major portion of Tigard's physical footprint stands on some of the most rotten and slide prone geology in the state, and given that a veritable river sometimes runs through it, maybe that aspect of the city's development standards ought to be more well-studied and more effectively addressed?
Afterword - CWS is in the process of updating its Design and Construction Standards. It will be interesting to see if the final document addresses the issues associated with construction in slide prone areas to a greater extent than they appear to be addressed in Tigard's Municipal Code. Here's hoping...