Lemon Creek is located in the City and Borough of Juneau (CBJ), Alaska, five miles northwest
of downtown Juneau. The creek flows approximately seven miles east to west, from its
headwaters at Lemon Glacier to the outlet at Gastineau Channel. Several small, clear water
tributaries are included in the Lemon Creek watershed, which encompasses approximately 25
square miles of alpine and forested uplands, wetlands, and urban areas.
The Alaska Department of Environmental Conservation (ADEC) has identified Lemon Creek as
an impaired water body, due to sediment, turbidity, and habitat modification. Designated,
protected uses for Lemon Creek water include drinking source water, industrial and agricultural
source water, contact and non-contact recreation uses, and growth and propagation of aquatic life
and wildlife (Alaska’s Water Quality Standard Regulations, 18 AAC 70). ADEC lists urban
runoff and gravel mining as primary pollutant sources to Lemon Creek (ADEC, 1995).
In the fall of 2002, the CBJ expressed concern about potential flooding in the lower, urbanized
portion of Lemon Creek. Past gravel mining operations have provided a much-needed source of
gravel for local construction projects, with the added consequence of lowering the streambed and
increasing flood conveyance. Since no in stream gravel mining has occurred during the past 20
years, the streambed has aggraded over time. The channel’s capacity has been reduced,
effectively increasing the likelihood of flooding of adjacent structures during major storm events.
Prior studies of the affects of gravel deposition on channel capacity were conducted. In 2002,
the USGS surveyed 42 cross sections and developed a provisional HEC-RAS river hydraulic
model along Lemon Creek from above Egan Drive to above the gorge. In 2003 and 2004, the
USGS repeated the survey of a number of these cross sections. The USGS calibrated the
provisional HEC-RAS model to a 2004 high flow event. In the fall of 2002, the CBJ hired Inter-
Fluve, Inc. to conduct a reconnaissance level sediment transport study, documented in a report
submitted to the CBJ in the spring of 2003. Findings indicated that gravel deposition would
continue, possibly at problematic levels in response to individual flood events. A number of
recommendations were made including further study of the Hidden Valley area to better
understand the sediment supply reach and an analysis of sediment management alternatives.
Several state and federal agencies responded to the City’s request for assistance in developing
sediment management alternatives that reduce flooding potential while conserving fish and
wildlife habitat. Subsequently, CBJ, Alaska Department of Natural Resources (ADNR) – Office
of Habitat Management and Permitting, Alaska Department of Fish and Game (ADF&G) – Sport
Fish Division, U.S. Fish and Wildlife Service (USFWS), and the U.S. Department of Agriculture
– Natural Resources Conservation Service (NRCS), signed a Memorandum of Agreement in
March, 2004 (Appendix A) as a cooperative commitment to this project. The purposes of this
study are to:
· Assess the geomorphology and sediment transport regime of Lemon Creek,
· Identify potential sediment management alternatives,
· Identify fish and wildlife habitat protection and rehabilitation opportunities, and
· Educate property owners within the watershed about the findings of this study.