Delta River

The Delta River flows for about 80 mi (130 km) through central Alaska, flowing north through a pass in the Alaska Range to the Tanana River.^[1] The source of the river is Lower Tangle Lake, the lowest of the Tangle Lakes chain to the west of Paxson, Alaska.^[2][1]

From its source, the Delta flows at a low velocity for about 2 miles (3.2 km) north, through a series of small pools and riffles, before descending a 15 ft (4.6 m) waterfall. After this fall, the river narrows from 130 to 60 ft (40 to 18 m) in width and gains an increased velocity. About 4 miles (6.4 km) upstream from the falls, the river slows and widens again, splitting into several channels with sand and gravel bottoms. About another mile further upstream, it slows more, and widens to a channel about 100 ft (30 m) wide and 3 ft (0.9 m) deep.^[2][1]

Ten miles from its source, the Delta River receives its first major tributary along its western bank, Eureka Creek, which carries meltwater from various glaciers along the southern face of the Alaska Range. This is followed by various other minor tributary streams until its confluence with Phelan Creek 6 miles (9.7 km) upriver, which drains the Gulkana Glacier.^[1] After this, it enters a narrow pass running through the Alaska Range, and flows north through the mountains for about 13 miles (21 km), as it receives meltwater from glaciers and various steep mountain streams. Among the largest glaciers in the region, the Black Rapids Glacier, drains into the river at a site called Black Rapids. The average elevation of the river during this section is about 2,400 ft (730 m), flanked on either side by the adjacent mountains of the Alaska Range, which range in elevation from 6,000–9,000 ft (1.8–2.7 km) at their summits.^[1][3]

About 9 miles (14 km) after Black Rapids, the valley grows shallow, and the Delta runs through an expanse of glacial moraines for about 25 miles (40 km). After this, it flows through a wide stretch of glaciofluvial fans for the last 16 miles (26 km) of its course. At the beginning of this section, it lies in a valley that descends to up to 200 feet (61 m) beneath the surface of the fans, decreasing to about 50 feet (15 m) near its mouth. About 10 miles (16 km) from its mouth, the Delta takes in its last major tributary, the 40-mile (64 km) long Jarvis Creek, which originates from Jarvis Glacier on the north face of the Alaska Range.^[1] The Delta River meets the Tanana River adjacent to the settlement of Big Delta, Alaska,^[4] which eventually drains into the Yukon River and thus the Bering Sea.^[5]

The water of the Delta River is extremely clear from its source to its confluence with Eureka Creek, after which it becomes more silty and fast-moving.^[6] Its broad flood plain is interrupted by various braided channels. It presents little flooding risk to communities along the river, as its western bank (on which no settlements are located) is lower than its east bank. However, lateral erosion along the eastern bank does pose a threat to homes and roads, prompting the installation of groynes (flow-regulating structures) along the bank by the early 1980s.^[7]

Large glaciers in the Alaska Range such as the Black Rapids Glacier, Canwell Glacier, and Castner Glacier run through the mountain valleys and drain into the Delta, as do various glacially-fed mountain streams.^[8][1]

The geology of the Delta River area is highly complex, including both Precambrian-era metamorphic rocks and recent volcanic and alluvial deposits. Much of the region is in the Wrangellia Composite Terrane, a crust fragment containing primarily oceanic rocks, with basalts, carbonate rocks, and mafic and ultramafic rocks as intrusives. Various glacial deposits from the Quaternary period are found throughout the area, forming eskers, moraines, kettles, kames, and outwash plains.^[15]

Besides the Delta, three other rivers cut a north-south track through the Alaska Range: the Nenana, Nabesna, and the Chisana. These likely predated the uplift of the Alaska Range around 25 million years ago, eroding a valley along their original course as the range rose.^[1]

The upper portions of the basin, between the Alaska Range and the Amphitheater Mountains, contain large amounts of economically-useful minerals, such as platinum group metals, nickel, cobalt, and copper. Small-scale mining operations have occasionally mined gold in the region.^[16]

About 33 species of mammals are attested in the Delta River basin. These include caribou of the Nelchina herd, Dall sheep, and moose. Black bears are frequently found on the flood plains and stream terraces, while grizzly bears are mainly found in the uplands, descending into the river valley during salmon spawning season.^[20][5] Foxes, wolves, lynx, snowshoe hares, martens, otters, and wolverines found in the basin are common targets for hunters and trappers.^[5] Bison live in the area north of the Alaska Range, between the Delta River and the Gerstle River.^[5]

About 135 species of birds migrate to the Alaska Interior during the summer months, with around 35 more arriving in other parts of the year. Waterfowl such as tundra swans nest in lakes and ponds in the river basin, while bald eagles nest and fish along the river. Spruce grouse are frequently found in the basin's spruce forests.^[20] The BLM-protected trumpeter swan can be found in the Tangle Lake wetlands.^[5]

Fish known to inhabit the Delta River include northern pike, Alaska blackfish, burbot, longnose sucker, and slimy sculpin. The salmonoids attested in the basin are Arctic grayling, lake trout, Dolly Varden trout, coho salmon, least cisco, and Bering cisco. Salmon do not use the river to spawn, due to high falls and high amounts of silt entering the river from Eureka Creek.^[5][21]

The Danish-Canadian botanist Erling Porsild and his brother Robert Thorbjørn began botanical studies of the Delta River area in 1926, while hired by the Canadian government to monitor Arctic caribou populations.^[6] Much of the Delta River basin consists of spruce and birch forests, with black spruce and white spruce alongside paper birch, willows, and poplar trees. Larix laricina larch is found in the northern floodplains, while pockets of quaking aspen dot the basin. Plants such as Labrador tea, grasses, and sedges form the understory of the forests. Alpine regions of the basin consist of meadows, barrens, and conifer forests, with plants such as mountain hemlock, deer cabbage, heather, lichens, and shrubs.^[22][23]

The upper portions of the Delta River and its tributaries in the Tangle Lakes lie within the Tangle Lakes Archaeological District, a National Register of Historic Places district containing 600 documented archaeological sites. The sites contain artifacts from ancient hunter-gatherers, with occupation attested from over 10,000 years ago.^[24] Native hunting trails and routes ran through the Delta River valley, often passing over the tops of eskers and the rims of plateaus.^[25]

A band of the Upper Tanana Athabaskans lived on the north slopes of the Alaska Range along the lower Delta and Goodpaster Rivers, hunting caribou, dall sheep, and moose.^[26][27] The Ahtna, present across the Copper River basin to the south of the Alaska Range, lived in the portions of the Delta watershed above the Black Rapids.^[28] The Delta valley may have been the main troute between the Upper Tanana and the Ahtna, who had overlapping territories in the region, as well as some trade and marriage relations.^[26][29][30] The photographer and adventurer James T. Geoghegan in 1904 recorded "Thothendig" as a native name for the river.^[31] The Middle Tanana name for the river is Niithaayh Ndiige, meaning "sandy gravel bed river", a name shared by the Johnson River and Delta Creek.^[32]

The American army officer Henry Tureman Allen named the Delta River during his 1885 expedition, naming it after its braided channels, which he found reminiscent of the networks of distributaries found in river deltas.^[1] An 1898 expedition by another army officer, Edwin Forbes Glenn, became the first westerners to travel through the Delta valley following advice from indigenous guides, who judged it to be the easiest route through the Alaska Range.^[33] Gold was discovered near Eureka Creek around 1900, prompting the creation of the Eureka Creek Mining District and around 250 miners to work in the area over the following decade.^[5]

The Trans-Alaska Military Road was laid down through the Delta valley during the first decade of the 1900s, as part of a project to connect Valdez on the southern coast with Eagle on the upper Yukon.^[34] In 1904, the U.S. Army established a telegraph station along the road at the mouth of the Delta River; this station grew into the community of Big Delta, Alaska. In 1919, Delta Junction was established to the south of Big Delta as a construction camp for the Richardson Highway, running along the river valley.^[12]

In the 1950s, agricultural developments begun around Delta Junction. A state agricultural plan in the late 1970s and 1980s cleared more than 110 square miles (280 km²) of land in the surrounding area for cultivation.^[12] However, most of the Delta River area remains undeveloped wilderness.^[20]

Land use and management

In December 1980, the Alaska National Interest Lands Conservation Act designated a portion of the Delta River as the Delta Wild and Scenic River Corridor, part of the National Wild and Scenic Rivers System. This designation included the upper portions of the river's course, as well as the Tangle Lakes and their tributary, the Tangle River.^[5][24] Described by the managing Bureau of Land Management (BLM) as "one of the few easily accessible wild and scenic rivers in Alaska", the basin is used for recreational activities such as wildlife watching, fishing, hunting, trapping, camping, and skiing. Recreational boating is also popular along the river and the Tangle Lakes.^[5]

The Richardson Highway runs along the corridor, meeting the Alaska Highway at Delta Junction. In addition to the corridor, the BLM administers the area south of the Denali Highway, which runs across the river, as well as large portions of the region west of the Richardson Highway. Beyond this, much of the land is administered by the Alaska Department of Natural Resources.^[35][24][36] A portion of the Trans-Alaska Pipeline System runs through the valley, mostly parallel to the Richardson Highway.^[37] The U.S. military base Fort Greely and the associated Donnelly Training Area cover about 710,347 acres (2,874.67 km²) of territory to the south and west of Delta Junction.^[38]

A BLM campground and limited commercial facilities are located along the Richardson Highway. It is frequently used by backcountry campers, fishers, and hunters. Although suitable campsites are common around the Tangle Lakes, they become very scarce along the upper Delta River itself, resulting in a lack of firewood, frequent fire rings, and trampled vegetation. Campsites become more common in the lower portions of the river, resulting in less environmental damage.^[20]