4. GENERAL ROAD USE PATTERN

This chapter has been designed to give an overview of the transportation system in the Toutle Block of the Washington State Department of Natural Resources. We will discuss some of the problem areas and different goals we had for this project. To finish off the chapter, we will discuss the different proposals as to what transportation systems to use, different options that are present, and how these options were developed.

 

1. Current Road Systems

The Toutle block has been heavily roaded from past harvests in the area. This has left a well defined system of roads traveling in and out of the unit. The major routes travel east/west and are linked by various sub roads. There are basically five main routes in the area and these are what will be focused on. These routes consist of the 4100 which is the mainline, 4200/4250/3000 commonly known as the ridge-top road, 2730, 4600, and the 5100. The last three are mid-slope roads that are used to route the harvest to either the Ridge-top road or the 4100. Figure 4.1 shows a graphical view of the roads.



Figure 4.1 Overview of main roads in Toutle Block.

 

1. The 4100 Main Line Road

The 4100 is the mainline traveling in and out of the Toutle Block. It has been build along the South Toutle River and is well graded and has moderate grades and curvature. This road is administered jointly by DNR and Weyerhaeuser. In the floods of 1995 and 1996, a substantial amount of damage was sustained to the east end of the road including the loss of the Herringotn Bridge which basically isolates the Weyerhaeuser unit and major portions of the DNR unit from using the 4100 main line, historically the preferred and most economical route.

 

2. Ridge-top Road

This road is travels along the ridge and consists of three roads. These roads are the 4200, 4250, and the 3000. This road accesses the north side of the ridge and the upper higher altitude portions of DNR’s lands. The 4200 and 4250 are currently being used for access thinnings.

 

3. The 2730 Road

Connects the top ridge road to the 5605 and the bottom of the hill. This is the alternate of choice connecting the east portion of 4100 past the Herrington Bridge washout to the west side of the 4100 in the event that the Herrington Alt is not built. This road has portions with grades near 15%.

 

4. The 4600 Road

Mid-slope road that connects the west section of DNR lands to the Ridge-top road and the 4100. Currently being used for thinnings and is in pretty good condition.

 

5. The 5100 Road

Mid-slope road connecting the 4600 to the 5140, 5145, and 5103. The west side of the 5100 has been washed out by the Toutle River and can not be built in the same spot due to a rock cliff (see Figure 4.2 and 5.2). The 5103 is proposed as a link down to the Herrington Alt Bridge site. The 5140 and 5145 are of interest as links to the 2730 in case the bridge is not built.

 

2. Current problems

In the springs of 1995 and 1996, flooding on the Toutle and various other tributaries to the Toutle caused large scale damage to the 4100 and other roads within the Toutle Planning Area. The types of damage included slides, road washouts, blocked culverts, and road slumps. The areas that we were most interested in were the 5100 and the 4100.





Figure 4.2 Location of 5100 Washout at base of rock cliff

The 5100 road washed out in two places, at the 14 Mile creek (culvert failure and washout) and just west from it where the road washed away at the base of a rock cliff from actions by the Toutle (Figure 4.2 and 5.2). The road was built as a full bench cut into the face of a cliff. We looked for an alternative route that would connect the 5100 to the 4600 further up 14 Mile creek.

The 4100 main line sustained significant damage. The first thing that we looked at was the Herrington bridge washout (Figures 4.3 and 4.4). The Herrington Bridge actually consisted of three bridges that spanned the Toutle on a large flood plain. It was determined that the bridge could not be built in the same location so an alternative site was found west of the original location (Figure 4.4).



Figure 4.3 Old Herrington Bridge Crossing, viewed from south looking north, across the washout.



 

Figure 4.4 Herrington Bridge Alternative Location.

There are also large portions of the 4100 east of the Herrington Bridge that sustained major damage (Figure 4.5). Damage includes being washed out by the Toutle and other tributaries. These various damages are discussed in Chapter 6 in more detail.

 



Figure 4.5 Damage to the 4100 east of the Herrington Bridge.

When analyzing the road system it became apparent that some additional road links required careful assessement. These sites are the washouts on the 5103, 5140, and the 5145 (Figure 4.6 and 4.7). These three crossings are on the same stream and were all washed out at the same time. Currently the DNR is preparing to put a culvert onto the 5140 which is the middle washout.



Figure 4.6. Locations of culvert failures and road washouts on the 5103 (lowest crossing), the 5140 (midslope crossing) and the 5145 (highest crossing). All crossings are on the same creek.



Figure 4.7. 5140 washout, viewed from east side of road looking west.

 

Weyerhaeuser land in the back end of the Toutle has been isolated by bridge washouts in the back end, the same flood event which also took out the Herrington Bridge. The upper reaches of the South Fork of the Toutle form large flood plains, up to one mile wide. In the past, stringer bridges crossed the main or side channels with the access roads build on approaches in the flood plain. Current view held it that no construction activity could take place within the flood plain itself. The only option would be to follow past practices with a temporary approach in the flood plain and a temporary bridge across the channel which would be removed each winter. However, such an approach would require road construction in the flood plain itself. No feasible crossing was found in the upper reaches that would span the river and/or flood plain.

 

3. SNAP

The Silviculture and Network Analysis Program, also known as SNAP, was used to do an analysis of the transportation system within the Toutle Planning Area. SNAP uses a set of polygons that are set up as harvest units and the transportation system to an analysis of the best routes of travel between the harvest site and the mill.

1. SNAP Variables

The constants that we used in SNAP were for the bridge costs, culvert costs, various road costs and speeds. These constants are:

• $200,000 cost for the Herrington Alt
• $ 174,000 for the approaches to the Herrington Bridge (~60 station of new construction)
• $90,000 as cost for 5103 bridge
• $7000 cost for 5140/5145 culverts
• Speeds of 32 mph for 4100
• Speed of 27 mph for Ridge road
• Speed of 22 mph for main mid-slope roads
• Speed of 12 mph for all other roads
• the 5100 washout is not replaced, all timber east of the 14 Mile creek has to move east via the 5103 or 5140/45 road system in order to get to mills
• No harvesting on Weyco Lands

Truck performance data such as speed were developed based on truck simulation runs discussed in more detail in Chapter 7.

1. Results

A transportation analysis over time was required to determine the timber flow or volumes over the various road segments. SNAP would select a road pattern that would result in the highest return, given various constraints such as construction cost, discount rates, location of and timing of harvest. As such the solution would outline the road system used. Of special interest were the following road links, specifically if the analysis would select them despite the high construction cost such as the Herrington bridge replacement.

• Herrington Alt. Bridge route including approaches. Intuitively assumed that the bridge despite its capital costs is still more economical in the long run given the timber volume that will go out over the years.
• use of the 4100 Alt; the only option to get timber out from the very end of the unit. Question is when will that happen. It also served as the major exit route for Weyerhaeuser timber. However, with no feasible crossing the road will serve DNR timber only.
• use of the 5103 Bridge versus 5140/5145 road link use (The 5140 and 5145 are culvert crossings higher up on the creek, above the 5103 Bridge; reconstruction costs are significantly lower, however, haul costs are higher because of increased travel distance). The 5145 route becomes the route by default if no bridge crossing is available. The question is, will timber East from the 14 Mile creek still use that route and then travel down to the bridge and 4100 mainline, or will it select the shorter route via the 5103 road with an expensive bridge.

Three runs were completed. Two runs had all the road links potentially available but differed in the allowable harvest limit. One run was restricted to 30 MMBF per period (one period equals 5 year) and the other run had no restrictions placed (see discussions in Chapter 3). The third run served as a baseline where the Herrington Bridge was NOT available, forcing timber haul to the ridge-top. In the first two runs (all road links potentially available and open) the selected road pattern would be the most economically.

A summary of the major points based on the two runs:

• Herrington Bridge
• SNAP builds bridge in first period of both runs where the bridge option is available
• Used throughout the 70 year cycle
• East End of 4100 Road
• Not used in first 20 years for any of the runs (timber age mostly about ~20 years)
• Used in later years for all runs (indicating the maturing of the timber in the back of the unit)
• 5103/5145/5140 Washouts
• 5103 built in first period when Herrington Alt Bridge is available
• 5145 only built when Herrington Bridge not available, indicating the default route to the ridge-top road system (2730/4200)
• 5140 not used in any scenario

A review of the results indicate the following. The Herrington Bridge should be built as soon as possible. It is being used as soon as it becomes available. There is an additional element that needs to be considered. With the 14 Mile Creek not passable, all the timber East from that creek has to move East and eventually over the Herrington Alt Bridge. The options are over 5140 or 5145 requiring stream culvert replacement, and then via the 5605/5600 road down to the Herrington Alt Bridge. The other option is via the 5103 road, requiring a bridge to eventually get to the Herrington Alt Bridge.

To provide a sense of the magnitude of timber flow over time at various points of interest six locations were selected (Figure 4.8). These points are at the Herrington Alt Bridge, beginning of 4100 Alt, 5145 Culvert, 5103 Bridge, and the 2730 connection with the 4250.

Our results are shown in Tables 4.1 and 4.2. Table 4.1 has the results from the Herrington bridge run containing a harvest limit of 30 MMBF per period. Table 4.2 contains the results from the analysis without the Herrington Bridge in place. This run also had a 30 MMBF harvest limit. To view the paths that SNAP chose for the first four periods, look in Appendix C.

Early harvest volumes over the Herrington Bridge are light. They come primarily from thinning, east of the 14 Mile creek using the route over the 5103 connection and areas above the new bridge location. They follow, of course, the silvicultural regime as discussed in Chapter 3.4. After period 5 a significant increase in harvest volume will take place which will also be reflected in an increased timber haul across the bridge. Early volumes are primarily the result from thinning projects, reflecting the general age pattern and distribution in the unit. As a result the two roads that access the eastern portion of the unit, the 4100 Alt and 3000 road, do not show any use until about period 4 and 5. That reflects the timber age distribution with most of the timber in the East end currently about 20 years old.

Timber volume on the 5103 and 2730 roads are primarely thinning in the early periods.

It also shows that the 5140/5145 roads are not being used given the availability of the 5103 bridge.

With the Herrington ridge closed no volume goes across it. Traffic is now directed to the ridge top road system and eventually the 4200 road. Timber from the lower slopes along the Toutle will move along the 2730 road system. Timber which eventually will use the 4100 Alt will go up the 2730 road. (see earlier comments on age distribution, Chapter 3.4). Timber that comes from the area East of the 14 Mile creek now has to get to the ridge top likewise. In so doing it favors the upper road system such as the 5145 which eventually feeds into the 2730 road. No traffic is observed over the 5103 road link. That link is obviously completely dependent on the bridge across the Toutle.

Currently DNR has been planning to replace the culvert on the 5140 road, the middle road on that particular stream that is crossed by the 5103, the 5140 (middle) and the 5145 (upper crossing). Given current analysis it appears that either the 5145 or the 5103 should be replaced. If the decisions is made to build the Herrington alt Bridge, then the 5103 link is the crossing that should be built. In that case neither the 5140 nor the 5145 serve any purpose. To the contrary, any crossing structure above the 5103 poses a potential risk in future failures. We hypothesize that all three crossings were destroyed in the same event with the top crossing (5145) washing out first and then cascading downstream, taking out the 5140 and 5103 culverts. Given the debris loading and material still stockpiled behind the failed 5140 crossing it is appropriate to consider a bridge for the 5103 crossing rather than a culvert. With the clearances available with a bridge any possible debris torrent most likely will wash underneath. A culvert and fill in its place may result in another washout ( see also design discussions in Chapter 5).