• A northern section of 0.6 mile length, north of Griffith Park, that is approximately bisected by bridges at Riverside Drive and the I-5 freeway.
• A main section that starts below Zoo Drive and the Ventura Freeway, 1.0 mile downstream from the northern section, and extends 5.7 miles southeast, nearly to the I-5 crossing by Elysian Park.

Throughout the Glendale Narrows channel, FoLAR volunteers collectively counted about 90 "medium" Arundo clumps in the 20'-50' size range, about 42 "large" stands in the 50'-100' size range, and measured a composite length of 3380 ft of "extra-large" stands exceeding lengths of 100 ft. These totals are approximate because volunteer team assignments overlapped and duplicate reports differ somewhat. If the "medium" clumps are assumed to average 35 ft in length and the "large" clumps average 75 ft, results from different teams can be converted to composite lengths and averaged for each reach.

The medium, large and extra large clumps counted by FoLAR volunteers yield total net areas similar to the aerial photo mapping results if the linear clumps are assumed to be 20 ft wide upstream of Los Feliz Blvd., 30 ft wide between Los Feliz Blvd. and the Glendale Freeway, and 38 ft wide downstream of the freeway. These assumed average widths are consistent with field observations.

The semi-quantitative survey method employed by FoLAR volunteers was feasible owing to unique features of the Glendale Narrows channel: uniform channel width, good visibility from bikepath on levees, and abundant landmarks for positioning.

To estimate the fractional degree of Arundo invasion at Glendale Narrows, we can estimate that the channel width is 35% land above Fletcher Drive and 65% land below. Above Fletcher, the gross channel area is 82 acres, of which about 29 acres are vegetated land, of which about 7.5% is occupied by 2.1 net acres of Arundo. Below Fletcher, the gross channel area is 67 acres, of which about 45 acres is land, of which about 14% is occupied by 6.3 net acres of Arundo (Photos 4 and 5).

Map 3 juxtaposes the aerial photograph and GIS map with the largest Arundo stand in the Glendale Narrows channel, with a length of 700 ft. and net area of about 0.9 acre, south of the Glendale Freeway next to Taylor Yard.

Along a half-mile reach below Los Feliz Blvd. to the Sunnynook pedestrian bridge, North East Trees removed Arundo in 1998, with project costs paid by a Los Angeles County Proposition A grant. The procedure was to access islands via temporary scaffolds, cut the Arundo using chainsaws, and spray resprouts with dilute Rodeo herbicide. Four years after treatment, the cleared area remains free of Arundo.

The upper half of Glendale Narrows warrants a high priority for Arundo control for these reasons: (1) the infestation is relatively light; (2) the area already cleared by North East Trees is vulnerable to re-invasion; (3) the Army Corps of Engineers Operations Branch has already approved invasive weed removal work at Glendale Narrows. The lower half of Glendale Narrows, below the Glendale Freeway, is assigned a medium-term priority owing to its downstream location and greater degree of infestation.

Much of the Arundo growing in the channel at Glendale Narrows is amenable to control by foliar spraying of full-height stalks after those near native vegetation are manually pulled down and compacted, according to Jason Giessow, project manager for the Santa Margarita & San Luis Rey Weed Management Area. This application method should reduce control costs per acre significantly below that for chainsaw clearance. Additionally, some clumps in the channel have been partially or completely flattened by recent flooding and could be easily treated using backpack sprayers (Photos 5 and 6).

Castor bean plants and eucalyptus are uncommon in the Glendale Narrows channel, absent or counted at rates of one to several per 500 ft. reach. Fan palms are more numerous below the Glendale Freeway, where several reaches have 10- 30 trees taller than 6 ft. and one dense grove between Forney and Riverdale Streets contains more than 80 tall palm trees (Photo 7). Young fan palms that were not counted are locally numerous.

The Army Corps of Engineers Operations Branch would welcome removal of non-native plants from the Glendale Narrows channel, which would help to maintain flow capacity at flood levels, but is not planning to fund such work due to other priorities elsewhere.

The Los Angeles River channel crosses the basin diagonally to the street grid and is vegetated for a distance of 2.0 miles. Entering the basin from the west, the channel is concrete-floored to a railroad bridge near Louise Street. The next 0.9 mile, from the railroad crossing to the vicinity of Lake Balboa, is a thickly vegetated soft-bottom trapezoidal channel with concrete sides. Over a distance of 1.1 mile from Lake Balboa to Burbank Blvd., the channel is unconfined, notably straight but with variable width, and until September 2001 contained sizeable Arundo stands. Between the Burbank Blvd. Bridge and Sepulveda Dam outflow gates, a distance of 0.4 mile, the channel is sparsely vegetated owing to long-term periodic clearance work by the Army Corps of Engineers.

Riparian vegetation is also present along tributaries that join the Los Angeles River within the flood control basin: Bull Creek and Haskell Creek on the north side and Encino Creek on the south side. All are concrete-lined outside the basin perimeter. During Fall 2001 contractors employed by the Army Corps of Engineers used bulldozers to excavate dense stands of Arundo from the Los Angeles River channel between the Bull Creek confluence and Burbank Blvd. Bridge. Arundo resprouts were sprayed with glyphosate herbicide 1 to 2 months after clearance. The cleared area is approximately 10 acres, estimated from aerial photographs, distributed along 1.1 mile of channel length (Photo 8).

Although castor bean was removed by the bulldozer operation, remaining in the cleared channel are at least 14 eucalyptus trees, mostly large, and small numbers of fan palms, none tall. Upstream of the cleared area, Arundo remains in the main channel west of Balboa Blvd. This section was divided into six 500-ft reaches and surveyed by a FoLAR volunteer team, which reported 19 small Arundo clumps, 17 medium clumps, and 1 large stand. Using average clump dimensions assumed for Glendale Narrows yields a net area estimate of about 0.6 acre; cursory mapping on the aerial photograph indicated an area of 0.9 acre.

According to the FoLAR volunteer team, the soft-bottom channel between the railroad bridge and Balboa Blvd. also contains 40 large castor bean plants, 33 eucalyptus trees, 128 fan palms, and one tamarisk tree -- giving this short riparian channel one of the more diverse weed populations of the watershed.

Elsewhere in the Sepulveda Basin, Arundo is abundantly present along two tributaries, Bull Creek and Encino Creek.

Bull Creek is a narrow, straight, unlined ditch through the basin, 0.5 mile long and located 0.2 mile east of Balboa Blvd. Arundo stands have an average width of 30 ft, composite length of 1000 ft, and net area of about 0.7 acre. A half-dozen large Ailanthus are present at the north end and castor bean is abundant near Lake Balboa. The Arundo infestation on Bull Creek is targeted for removal by the Army Corps and City of Los Angeles Recreation & Parks Dept. as part of a proposed channel reconfiguration project.

Encino Creek enters the flood control basin at its south margin near Havenhurst Ave. and flows 0.8 mile in an east-northeast direction to its confluence with the Los Angeles River below the Burbank Blvd. Bridge. The riparian corridor is bounded on the north by Burbank Blvd. and on the south by agricultural fields, the athletic field, and the parking area of Hjelte Sports Center. The riparian zone varies in width from 200 ft to 300 ft, and has an area of about 24 acres. Dispersed Arundo stands occupy 1.2 acres, or 5 percent of the riparian area, as measured by mapping clumps on aerial photos; Map 5 is the resulting GIS screen display. The land is flat and appears amenable to clearance using a hammer flail mower beneath the tree canopy. The dominant non-native tree along Encino Creek is tropical ash or Shamel ash, which may constitute more than 30 percent of the biomass. Additionally, numerous eucalyptus saplings are present near Havenhurst Ave.

On the eastern side of Sepulveda Basin, Haskell Creek flows southward between Woodley Ave. and the dam, and intersects the Los Angeles River below the Burbank Blvd. Bridge. Much of the riparian corridor is within the Sepulveda Wildlife Reserve, managed by City of Los Angeles Recreation & Parks Dept., where Arundo, castor bean, small eucalyptus, and tropical ash have been mostly controlled for a number of years. Abundant castor bean remains north of the reserve near the Tillman water reclamation plant.

Overall, the Sepulveda Basin now contains about 2.8 acres of Arundo, compared to 13+ acres less than one year ago. Although Arundo infestations along Bull Creek and the main channel west of Balboa are upstream of the recently cleared channel east of Balboa, these channels probably are not subject to erosive flooding so do not necessarily warrant high priority for Arundo removal. However, a consortium of environmental organizations that advises City and Army Corps staff on management of the wildlife area is advocating control of invasive weeds throughout the flood control basin, and that interest may influence the priority for funding more than regional considerations.

In Dry Canyon upstream of the riparian vegetation, according to Jo Kitz with the Mountains Restoration Trust, during Fall 2001 MRT staff and an Outward Bound Adventures crew removed 7 Arundo clumps near the intersections of Mulholland Highway and Old Topanga Canyon Road.

Further downstream, about 0.5 acre of Arundo occupies vacant private land near the junction of Wrencrest Drive and Old Topanga Canyon Road (Photo 9). Large castor bean plants are present also. Another 10 small Arundo clumps are present along the 0.7 mile-long unlined stream channel down to the start of the concrete channel above Spielberg Drive. Total area with Arundo is about 0.6 acre. Although the channel's habitat value is low, a medium priority for Arundo removal is justified by the fire hazard created by Arundo growing in a residential area.

An old eucalyptus grove of large trees is present between the confluence of the two canyons and the freeway, probably mostly planted around the lower constructed pond when it held water (Photo 11). Upstream of the confluence, Arundo is present as randomly dispersed clumps, several of medium to large size, for distances of 0.5 mile up Brown's Canyon (Photos 12-13) and 2.5 miles up Devil Canyon. The net areas are 0.4 acre in Brown's Canyon and 0.6 acre in Devil Canyon, for a total of 1.0 acre, as mapped on aerial photos.

The Arundo infestation in Devil Canyon originated from source stands planted years ago on rural property now occupied by a recently constructed gated community named Indian Falls Estates (Photo 14). Map 7 shows the GIS representation of Arundo populations in the two canyons.

Although parts of the two canyons may be privately owned, this area warrants a high priority for Arundo eradication, because (1) the infestation is relatively small, (2) the canyons are otherwise weed-free and nearly pristine in character, and (3) some Arundo clumps are clearly susceptible to erosive flooding which transports propagules downstream. One potential complication is a controversial proposal for high-density residential development, named Deerlake Ranch, on hills between the two canyons, reported by the March 11 Los Angeles Times.

Within Aliso Canyon, a 20-ft-diameter Arundo clump is present about 1400 ft north or upstream of Rinaldi Street. Three smaller Arundo clumps and abundant castor bean are present near the lower end of the natural channel at Rinaldi (Photo 15). No Arundo was observed from bike paths in the upper one-mile length of Aliso Canyon.

Elimination of Arundo and castor bean in Aliso Canyon can be assigned a high priority because the infestations are small, the natural flora looks diverse and healthy, and the property is protected as parkland.

Within Limekiln Canyon, Arundo is not present, castor bean has been cut previously but has resprouted, and the dominant non-native plants are large pine trees planted decades ago by the Recreation & Parks Dept. which appear to be propagating.

Above the reservoir, 10 small Arundo clumps were counted adjacent to the heavily wooded stream channel, distributed along a one-mile length that is followed by the county road through private inholdings with a small number of houses. One occurrence of Arundo, undoubtedly planted decades ago, is located beside an abandoned concrete swimming pool that was constructed in the stream's flood zone.

Arundo appears to be absent from the riparian zone upstream of the inhabited section. In the downstream direction, between the county road and Pacoima Reservoir, the channel was not surveyed due to postings of "no trespassing" signs. Below Pacoima Dam, a half-mile length of riparian woodland ending at Gavina Ave. is free of Arundo, but numerous castor bean plants are present along the access road to the dam.

Despite its private land ownership (Photo 16), the infested section of Pacoima Canyon is assigned a high priority for Arundo control in consideration of the small number and small size of clumps and otherwise pristine character of the alder woodland along the stream.

Two significant watercourses drain to Hansen Dam: Little Tujunga Canyon to the north, and the much larger catchment area of Tujunga Wash and Big Tujunga Canyon to the east, which extends 25 miles into the San Gabriel Mountains.

Although the Arundo infestation was not mapped on aerial photos, the channel is readily viewed from Little Tujunga Canyon Road. After estimating composite widths of nearly continuous Arundo stands along the canyon floor, the net area was calculated to be 12 acres. Despite the relatively high position of Little Tujunga Canyon in the Los Angeles River watershed, Arundo control warrants a medium priority in view of the already degraded condition of riparian habitat and the canyon's location above Hansen Dam which during strong flood events may block downstream transport of propagules to Glendale Narrows.

The higher Arundo population starts at Black Cargo Mine on Iron Mountain, at an elevation of about 4,200 ft, and extends 2 miles downstream along Monte Cristo and Mills Creeks. The lower population starts above the Stonyvale picnic area, becomes abundant among private cabins at Vogel Flat, and extends 5 miles down Big Tujunga Canyon to the Forest Service boundary above the County Conservation Camp. The Environmental Assessment proposes that a maximum estimated net area of 10 acres will be cut on Forest Service land; and although the report does not estimate the area occupied by Arundo on private inholdings, it does provide maps of infested riparian areas that suggest private ownership of 3 to 4 acres of Arundo.

Presuming that the 10 acres of Arundo on Forest Service land will be cut and treated during the next 3 years, clearance of private inholdings should follow without delay; thus the private land in Big Tujunga Canyon is assigned a medium-term priority for Arundo removal.

Exotic trees in Big Tujunga Canyon include Ailanthus near the Stonyvale picnic area, but these will not be targeted in the proposed action.

At the transition from Big Tujunga Canyon to the upper end of Tujunga Wash, Los Angeles DWP land extends southwestward about 2 miles from the outlet of Pipe Canyon to the vicinity of Oro Vista Ave. Arundo removal work managed by the California Environmental Project commenced in January 2001 and is still underway (Photos 17-18), funded by grants from the Los Angeles Urban Resources Partnership and the Center for Natural Lands Management. Approximately 5 acres was cut during 2001, half by a hammer flail mower and the remainder by chainsaw crews, and another 2-3 acres of Arundo remain that will be cleared during 2002.

South of the I-210 freeway, the County Public Works project area extends westward 1.2 miles from the Big Tujunga Nature Preserve near the southern freeway bridge to the eastern boundary of Hansen Dam Flood Control Basin. To mitigate flood control channel clearance work elsewhere in Los Angeles County, contractors cut 30 net acres of Arundo (Jason Pereira, pers. comm.) using a hammer flail mower and chainsaw crews between October 2000 and January 2001. Judging from aerial photographs, the area of riparian woodland is 75 acres approximately, of which 40 percent was occupied by Arundo in open clearings and under the native tree canopy. Across the project area, the abundance of Arundo diminished rapidly to the west, owing to entrapment of flood-carried Arundo propagules in the riparian woodland at its east end.

1. The western third contains landscaped parkland, visitor facilities and parking lots, and a densely wooded natural area of about 85 acres that is devoid of Arundo except for several clumps near the dam on the east side.
2. The central portion of the basin is occupied by a large elongated pond, over a half-mile long and devoid of vegetation on the banks, and large barren areas presumably scraped for gravel mining or flood control purposes. This section also includes dry upland scrubland. Small Arundo clumps are present in some of the sparsely vegetated areas and near the Little Tujunga channel outlet.
3. The basin's eastern third is the lowest still-natural part of Tujunga Wash, a dynamic terrain of active scoured flood channels, abandoned channels, and discontinuous riparian woodlands. The channel area under Army Corps jurisdiction has a rectangular shape in map view, with length of 4500 ft and width of 1000 ft, bounded by bluffs on both north and south margins. Measurements from aerial photos indicate that the woodland area is about 50 acres. Arundo present on the east side of the woodland is the downstream continuation of recently cleared infestations on County land, but is less prevalent.

South of San Gabriel Blvd., the 0.9-mile-long zone of riparian and wetland vegetation expands to a width of 0.5 mile near the dam and an area of 165 acres (Photo 20), excluding land that is mostly barren of vegetation due to oilfield operations and flood scour of the channel. Based on fractional mapping of Arundo stands on aerial photographs, the net total area of Arundo is about 35 acres, occupying about 21 percent of the vegetated land, in which the largest stand, a pure monoculture of Arundo, occupies nearly 10 acres. This lower part of the Rio Hondo receives flood water and Arundo propagules from the San Gabriel River, located 1.2 mile to the east, via an overflood channel that connects the two river courses.

Limited Arundo control projects have been undertaken at both ends of the linear riparian corridor upstream of San Gabriel Blvd. In 1997 the Mountains Recreation & Conservation Authority sponsored excavation of a 250-ft-long Arundo stand near the Bosque del Rio Hondo park; and in late 2000 contractors employed by the San Gabriel Mountains Regional Conservancy mainly foliar sprayed 2.2 acres of Arundo north of the Pomona Freeway, primarily near the upstream end of the riparian corridor, funded by a grant from the Long Beach/Los Angeles County Natural Resources Trustee Committee. The largest Arundo stand treated by the SGMRC project, with net area of 1.05 acre, is depicted on Map 11 which juxtaposes the aerial photograph and GIS map of the riparian corridor's upper end. An additional 0.8 area of Arundo was foliar sprayed north of the area shown, in a wide ditch between the golf course and concrete channel levee. North of the freeway 4.2 acres of Arundo remain untreated.

Two small tributary drainages join the Rio Hondo near the San Gabriel Blvd. Bridge. On the east side, Mission Creek has natural vegetation along its 0.8-mile-long channel starting at Rosemead Blvd. south of the Pomona Freeway. A program to remove 0.15 acre of Arundo plus castor bean and Ailanthus along Mission Creek was initiated in late 2001 by CH2M Hill to mitigate construction of a groundwater treatment facility by the U.S. Environmental Protection Agency. On the west side of the Rio Hondo channel, the oil field property adjacent to San Gabriel Blvd. contains about 1.7 acre of Arundo.

Other non-native plants abundant in the Rio Hondo riparian corridor include castor bean, Ailanthus, palm trees (Photo 21), eucalyptus, tropical ash, passion flower vine, and perennial pepperweed in a wetland area near the dam.