Tuesday, February 26, 2008

La Jencia Documentation

[Overview map of La Jencia jobsite. The flow is from bottom (South) to top (North).]

Although La Jencia watershed is subject to ephemeral flooding events, the creek itself is perennial from springs ~100m upstream of our jobsite to its confluence with the Rio Salado. There is ample evidence that this system has downcut substantially in recent years. In fact, current GoogleEarth satellite photos record a markedly different channel from the current one. The older channel was probably active within the last two years.
[Blue marks the channel recorded from GoogleEarth; Red marks the approximate course of the new channel. Note the linearization of the former meanders. #7 denotes the position of the next photo.]

On the ground it is obvious that this new channel is 3-5 feet lower than the previous channel/floodplain.
[Blue denotes approximate position of former channel; Red denotes current channel. The wetlands/spring in the bottom of the photo confirms continued subsurface flow along the old meanders. The bank with machinery on it is several feet above the new bankfull channel.]

Due to the lack of on-site building materials and other reasons, our project does not directly address the channelization and downcutting but instead attempts an oblique approach to these hydrogeomorphic issues; by suppling more vegetation to slow and absorb large flow events we can limit further erosion as well as build up biomaterial that could someday provide substrate to dam, sediment, and eventually reconnect La Jencia with its floodplain.
[Upper La Jencia 2008 Jobsite.]
[Lower La Jencia 2008 Jobsite.]

We planted ~700 cottonwood and a few thousand willow poles along both sides of the channel for approximately 1/2 kilometer above the road crossing. Light green along stream banks is willow, dark green denotes cottonwoods. This is a crude approximation to give some idea of the size and location of treated areas.
[Overview map with Key to documentary photographs. ]

Click on the photo above to enlarge it enough to see numbers marking the location and direction of each of the post-planting photographs] that follow:
[photo #0]
[photo #1]
[#4][photo #5]
Farewell, La Jencia.

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