United States Department of Agriculture
Pacific Southwest Research Station
General Technical Report
within 50 m
|Little Lost Man||Upper||141||52||None|
|Prairie Creek||Hope Creek||218||80||Minor|
|Zig Zag No. 2||22||25||Yes|
|r2 = 0.88 for debris loading vs. large redwood frequency.|
|Basin area (km2)||1.6/3.9||1.1||3.7||1.5||3.5/9.1||0.7||3.5||6.6||8.2||11.2||16.7||27.2|
|Pool to pool spacing|
(by channel widths)
|Area in pools (pct)||24/36||33||27||12||22/18||49||34||46||36||41||26||25|
|Area in riffles (pct)||30/30||25||14||26||15/21||21||46||49||20||15||18||25|
|Area in debris-stored|
|Area in undercut|
drop in elevation
|57/37||69||17||38||59/30||43||27||34||8||< 1||18||< 1|
|NOTE: Total percentages in stream environments may be less than or greater than 100 percent owing to overlaps between units (such as pools which contain debris-stored sediment).|
Woody debris jams in streams that drain old-growth forests are also quite stable. Large trees, found growing on pieces of debris which comprise the jams, are often more than 100 years old (Keller and Tally 1979). Considering the stability of debris jams in old-growth streams, Keller and Tally (1979) concluded that debris-related sediment storage capacity in Little Lost Man Creek (and other old-growth streams) provides an important buffer system for the channel by allowing infrequent large-magnitude sediment inputs to be stored in jams and released slowly over time. In contrast, debris-related storage capacity in North Fork Caspar Creek is less than 50 t km-2 (table 4), the presence of many collapsed or partially collapsed jams and the lack of mature trees growing through the debris pieces suggest that the debris jams are dynamic, short-lived features (Napolitano 1996; table 5). Historical logging activities may be the cause for these differences.
Caspar Creek was first logged in 1860, and most of the watershed was clearcut and burned between 1864 and the mid-1890's (Wurm 1986). Caspar Lumber Company records indicate that redwoods logged in the Caspar Creek watershed typically ranged between 0.8 and 2.5 m in diameter. Cut logs were floated downstream to the company mill located on the coast. To make this possible, a logging splash dam was constructed near the headwaters of the North Fork Caspar Creek (Jackson 1987a). The water stored behind the dam was released during large storms to increase streamflow enough to enable log drives. Before log drives could be conducted, a stream channel had to be "improved" by "removal or blasting of boulders, large rocks, leaning trees, sunken logs or obstructions of any kind" (Brown 1936). During each log drive thousands of logs were transported down the creek (Jackson 1987b).
|3.5||0.03||1.1||6.4||Hill slopes or|
|1Data for Little Lost Man Creek from Keller and Talley(1979)|
|2Mean channel width=channel area per centerline channel length|
|1 All Little Lost Man Creek data, and debris loading data for North Caspar Creek are from Keller and others (1981).|
|2 Remaining sediment storage capacity in debris jams.|
|3 Based on data in Keller and others (1981), and assuming sediment storage per unit drainage area is similar in upper and lower Little Lost Man Creek and bulk density of sediment in storage is approximately 1.8 t m-3.|
|4 North Fork Caspar Creek sediment storage based on data collected in summer 1987.|
Evidence of channel preparation for log drives along the mainstem North Fork Caspar Creek can be found by examining in-place old-growth stumps on valley fills. The old-growth redwood stumps are commonly obscured by mature stump sprouts or by shrubs growing through the stump. It is likely, therefore, that old-growth stumps are present elsewhere along the creek where they have not been recognized. As the valley width is narrow (3 to 20 m) along most of North Fork Caspar Creek, stumps were cut flush with the ground surface to avoid snagging of floated logs during drives. All other old-growth stumps in the basin (e.g., those farther from the channel and on hillslopes) were cut well above the root swell, several meters above ground surface, because sawyers were paid by the small diameter of each log that they cut (Jackson 1987a).
Direct evidence of removal of woody debris elements from the channel of North Fork Caspar Creek is difficult to find. Characteristics of woody debris within the active channel, however, suggest that logs were removed or blasted. For example, almost without exception, the largest logs in the channel today are 0.5 m in diameter, approximately the same diameter, as the largest second-growth trees within the basin. In one location, an old-growth trunk is protruding from the bank of a valley fill deposit. This trunk had been sawed obliquely, to be flush with the ground surface of the valley fill deposit. Before being cut, it probably extended across the valley width and obstructed streamflow, and thus would have hindered efforts to float logs downstream. Other smaller old-growth logs are similarly oriented and partially buried within the same valley fill deposit a few meters upstream, suggesting that there may have originally been a debris jam present at the site.
|Evidence from maps1|
|01||80 m upstream|
of xs 9
|1980||53||0-10m3||Jam formed in 1980, as noted in 1980 xs survey;|
bars and some LD first depicted on 1986 map
|02||25 m upstream|
|1984 or 1985||34||20-30 m3increase||LWD jam but no bars on 1985 map; xs 26 end-pins|
missing in 1986; step and small bar shown on 1986 map
|03||15 m downstream|
of xs 28
|Before 19792||71||0-10 m3||Few LWD pieces and no gravel bars on 1985 map;|
long bar on 1986 map
|05||8 m upstream|
of xs 37
|Before 19792||58||0-10 m3||Most bars and LWD are depicted on 1985 map;|
no significant changes 1986-87
|06||2 m downstream|
of xs 42
1979 and 19853
|73||0-10 m3||Stepping noted 1985; step breached 1986, but most|
stred sediment remained in jam
|07||15 m upstream|
of xs 43
|Before 19792||47||No change||No changes evident 1985-87|
|014||16 m upstream of|
1979 and 19853
|77||No change||No changes evident 1985-87|
|017||17 m downstream|
of xs 56
|Before 19792||32||0-20 m3 decrease||Step collapsed in 1986,|
but most stred sediment remained in jam
|024||26 m upstream|
of xs 60
|Before 19792||26||No change||No changes evident 1985-87|
|033||16 m downstream|
of xs 74
|Before 19792||33||0-20 m3decrease||No changes evident on maps; 1986-88 scour|
at xs 74 suggests a decrease in storage
|035||17 m downstream|
of xs 76
1979 and 19853
|27||No change||No changes evident 1985-87|
|Total storage as Large Jams (530 m3)|
|1 Based on analysis large woody debris maps (Unpublished USDA Forest Service maps) prepared in 1985 and 1986, and geomorphic maps prepared in 1987 (Napolitano 1996).|
|2 Based on review of cross-section field notes prepared in July 1979, which state whether large woody debris was present, and if it created a backwater at a cross-section.|
|3 No backwater effect from woody debris noted in cross-section field notes prepared in July 1979; debris jam shown on 1985 large woody debris maps.|
Channel erosion and incision would be promoted by increased peak flows associated with splash dam releases and abrasion caused by repeated transport of thousands of logs. A large fraction of the sediment stored in debris-jam backwaters would probably have been liberated because the logs that had stabilized and trapped the sediment were removed during channel preparation. Considering that the diameters of trees logged in Caspar Creek generally ranged between 0.8 and 2.5 m, the streambed may have degraded substantially where jams extended across the channel. Most of the sediment stored in valley fills, however, probably was not eroded because of the resistance to erosion afforded by large and extensive root networks of the old-growth trees growing on the fills.
Before the log drives, the mainstem channel is likely to have more closely resembled the present-day stream reach located upstream of the splash dam backwater. In that reach, the channel is only slightly entrenched (typically channel banks are less than 0.6 m high) and has a much higher width-to-depth ratio than below the splash dam. Its planform, typically, is anastomosing with a well-defined main channel and auxiliary high-flow channels.
Under present conditions, the largest second-growth trunks in the channel in the reach upstream of the splash dam do not appear to be mobilized by frequently occurring peak flows. Interactions between the forest and the channel in that reach are more likely to resemble those before the initial logging than would the interactions downstream where the logs are more easily mobilized.
Channel morphology in the reach above the splash-dam resembles that of Little Lost Man Creek, the old-growth channel in Redwood National Park which is similar to North Fork Caspar Creek in setting and physical watershed characteristics.
Lack of well-developed soil horizons on the valley fills suggests that the fills were frequently flooded, at least as recently as several hundred years ago (i.e., the time it would take for a A horizon to form). The fact that old-growth trees on the valley fills were cut flush with the ground surface suggests that those preparing the channel for log drives believed this was necessary to avoid snagging cut logs during drives, also suggesting that high flows regularly inundated the terrace surface. Bank tops along North Fork Caspar Creek are typically 1 to 2 m above the channel thalweg, much greater than stages associated with common flows (i.e., a stage of about 0.6 m has a recurrence interval of 6 yr at gaging Station A). This suggests that valley fills have been converted from large-volume, long-term sediment sinks (floodplains) to substantial sediment sources (terraces) as a result of channel incision in response to removal of old-growth debris jams from the channel during 19th-century logging activities. Conversion of the floodplains to terraces signifies a major change of trends in valley sediment storage and a pervasive alteration in the sediment budget for the basin.
The channel has not recovered its previous morphology because jams in the channel are now less stable, stepping is less pronounced with smaller diameter trunks, and the resistance to bank erosion afforded by second-growth trees on the valley fills limits lateral migration. These factors cause the channel to remain entrenched, and to have a narrower width-to-depth ratio than the reach above the splash dam. Comparison of second-growth to old-growth channels also shows that pools are much more frequent and their average depth is greater in the old-growth channels (Keller and others 1981, Montgomery and others 1995). Therefore, it is also likely that pools are less frequent and shallower in North Fork Caspar Creek as a result of historical logging activities. It is unlikely that North Fork Caspar Creek will recover its former morphology, however, until the former relationship between the size of woody debris and flow magnitude is reestablished.
Brown, N.C. 1936. Logging transportation. New York: John F. Wiley and Sons; 327 p.
Jackson, W. Francis, Historian and author, Mendocino, California. [In-person conversation with Michael B. Napolitano]. July 1987.
Jackson, W.Francis, Historian and author, Mendocino, California. [In-person conversation with Michael B. Napolitano]. August 1987.
Keller, E.A.; MacDonald, A.; Tally, T. 1981. Streams in the coastal redwood environment: the role of large organic debris. In: Coats, R.N., ed. Proceedings, Symposium on watershed rehabilitation in Redwood National Park and other Pacific coastal areas; 1981 August 2528; Arcata, CA. Sacramento, CA: Center for Natural Resources Studies of JMI, Inc.; 161-176.
Keller, E.A.; Tally, T. 1979. Effects of large organic debris on channel form and fluvial processes in the coastal redwood environment. In: Rhodes, D.D.; Williams, G.P., eds. Adjustments in the fluvial system. Dubuque, IA: Kendell Hunt Publications; 168-198.
Montgomery, D.R.; Buffington, J.M.; Smith, R.D.; Schmidt, K.M.; Pess, G. 1995. Pool spacing in forest channels. Water Resources Research 31(4): 1097-1105.
Napolitano, M.B. 1996. Sediment transport and storage in North Fork Caspar Creek, Mendocino County, California: water years 1980-1988. Arcata, CA: Humboldt State University; 148 p. M.S. thesis.
Tally, T. 1980. The effects of geology and large organic debris on stream channel morphology and processes for streams flowing through old-growth redwood forests in northwestern California. Santa Barbara, CA: University of California at Santa Barbara; 273 p. PhD. dissertation.
Wurm, T. 1986. Mallets on the Mendocino coast: Caspar Lumber Company, railroads and steamships. Glendale, CA: Trans-Anglo Books.