Geography of Menghe

Menghe lies on the southeastern section of the continent of Hemithea in Septentrion. Its northern border with Polvokia is defined primarily by the lower course of the White (Baek) River, and its southern border with Innominada, now Argentstan, is defined by the River Argun. Its other land borders, defined by treaty and generally not following waterways, are shared with Dzhungestan, Maverica, and the People's Republic of Innominada.

Menghe's geography is broadly defined by two major mountain ranges: the high Chŏnsan Range, which curves from the western border to terminate in the north, and the more moderate Donghae Range, which runs along the east coast and forms a fragmented highland pattern in the southeast. Between these mountain ranges is a large and relatively level plain, where abundant rainfall during the summer monsoon season feeds a rich network of rivers and lakes. Conventionally, this level area is divided between the Upper Meng Basin between the Chŏnsan and Donghae ranges, the Chŏllo Plain in Menghe's center-south, and the Kala-duzun plain in the southwest. The area northwest of the Chŏnsans, mainly comprised of arid steppe and scrubland, is known as Sansŏ, and the northern area of the country - usually demarcated by the boundary between the Meng and White River watersheds - is known as Bugrim.

Tectonics

Menghe's terrain was shaped by the divergence of the South Hemithean and East Meridian tectonic plates. The South Hemithean Plate, which includes nearly all of Menghe's territory, is currently drifting northwest away from a divergent boundary at the bottom of the South Menghe Sea. The Chŏnsan Mountains, which run from western Maverica to northern Menghe, follow a convergent boundary tracing the opposite edge. In north-central Menghe, they terminate with a transform boundary that runs northwest to resume convergence again in Polvokia's Buksan mountains.

The forceful westward movement of the North Helian Plate, which formed the islands of Dayashina and raised Polvokia's Northeast Plateau, applied additional convergent pressure. Though originally part of the South Hemithean Plate, and often grouped together with it on maps, the East Menghe Sea Plate and the Polvokian Lower Plate drift at slightly different angles due to the North Helian Plate's pressure, forming minor plates with their own tectonic boundaries. In Menghe, the convergent boundary with the East Menghe Sea Plate traces the Donghae Mountain Range along the east coast.

Physical regions

Chŏnsan mountains

The Chŏnsan mountains are Menghe's most defining geographic feature, dividing the country between southeastern and northwestern plains. They are the highest area in Menghe, and among the highest areas in Hemithea, surpassed only by the Buksan mountains in Polvokia. The highest mountain in the range is Mount Tae, or Taesan, with a peak 4,537.5 meters above sea level. With their sharp ascent and high altitude, the Chŏnsans end the northward drift of the Intertropical Convergence Zone in summer, dividing the country between abundant seasonal rain to the south and semi-arid steppe to the north.

The upper valleys of the range are lined with glaciers, fed by annual snow from the monsoon pattern. Meltwater from the glaciers feeds the heads of several of Menghe's rivers, including the Ro river to the south, the White river to the north, and parts of the Sŭllŭnge river into Dzhungestan. Several of these rivers, particularly the Ŭm and White, have carved out vast valleys. Because of its high peaks, unique scenery, and isolation from urban life, the Chŏnsan region is becoming an increasingly popular destination for Menghean and foreign tourists and hikers.

During the Menghean War of Liberation, the Chŏnsan range was the site of the Chŏnsan Expedition, also known as the Arduous March, in which General Yang Tae-Sŏng led the Eighth Army from Suksŏng to Jinjŏng. The Eighth Army's recorded route today serves as an attraction for Menghean nationalists, some of whom have retraced the route on foot.

Chŏllo

The Chŏllo Plain refers to the low-lying area between the Chŏnsan Mountains and the South Menghe Sea. Its western boundary is conventionally set at the Wŏl river, and its eastern boundary has been variously defined as the lower Meng watershed, the lower Meng river, or the foothills of the Donghae highlands. At its center is the Ro river, which, like the Meng, branches outward to link a historical network of barge-trading cities. The Chŏllo basin is slightly hilly, pushed upward by tectonic movement to the south, and gradually ascends to the foothills of the Chŏnsan range, where it abruptly rises to some of the country's tallest peaks.

The name Chŏllo (천로 / 千鷺) dates back to at least the 3rd century BCE, and means "thousand herons," likely a reference to the large flocks of marsh birds that visitors saw in its marshes and swamps. Note that this is written as chŏn-ro, but under Standard Menghean pronunciation, combined to form an "l" sound. Chŏllo's herons also brought the Ro river (로강 / 鷺江, Rogang) its current name, though prior to conquest by the Meng dynasty, locals knew it as the Wŏl river (越江).

Like the central basin, the Chŏllo plain is heavily influenced by monsoon patterns, but it is also warmer and drier in the winter. In ancient times its population was largely nomadic, especially in the north, but under Menghean imperial rule it developed into an agricultural region with a vast irrigation system feeding flooded rice paddies.

Rivers and canals

Meng river

Though not the longest river in Menghe - a title which belongs to the White - the Meng river (멩하 / 孟河, Meng Ha) is the most famous. Etymologically, its name can be translated as "eldest river" or "most eminent river," as it is much wider than the other rivers on its lower route and absorbs water from all tributaries in the middle of the country. The Meng river has a drainage area of approximately 978,000 square kilometers, including the entirety of the Meng plain, and much of that area receives heavy rainfall during the summer monsoon season. Glacial meltwater from the Chŏnsans and runoff from the West Donghae range feeds it during the drier months. It produces an average annual discharge of 20,638 cubic meters per second, but this can rise to 80,000 cubic meters per second during an El Niño flood season. Shortly before breaking up at its delta, the Meng reaches a width of 9 kilometers.

Historically, the Meng river formed an important cradle of Meng civilization. All three present-day Menghean-language names for Menghe - Dae Meng (大孟 / 대멩), Mengguk (멩국 / 孟國), and Menghwa (孟華 / 멩화) - refer to the Meng dynasty, which was named for the State of Meng, which in turn took its name from the river at its southern edge. Owing to its long length and many navigable tributaries, the Meng river system formed a vital transportation network in the days before the introduction of railroads, allowing barges to cheaply carry supplies between any major cities on the central plain.

The Meng river's many branches and winding course have led to some debate about its ultimate source. For much of history, only the 1,400-kilometer section south of Pyŏngchŏn was known as the Meng River; there, it divided into the Yi and Wu rivers. The first international figures for its total length used the Yi and Jang branches that flow through Bakgajang, for a total length of 2,191 kilometers; but in 1922, the official waterhead was moved to the foot of Mount Godongsan in North Donghae Province, and the entirety of the Yi river through Jinyi, which raised the overall length to 2,285 kilometers. This is generally accepted as the longest possible distance from the Meng river's mouth to any of its various sources.

From the early 20th century onward, the breadth of the Meng River posed challenges for transportation. South of Sapo, the river averages over 1.5 kilometers across, and while there are occasional reports of temporary pontoon bridges built during military campaigns, for centuries there were no permanent bridges on the Meng river proper. The two-level Junggyŏng Grand Bridge, built between 1925 and 1929, was the first modern crossing, and at 1,135 meters it was the longest bridge in Menghe at the time. In recent decades, a flurry of road and rail construction has overcome this barrier, and the longest Meng River crossing is over 8 kilometers in length.

White river

The White River (백강 / 白江, Baekgang) is also known as the Baek River. With a total length of 3,029 kilometers, it is the longest river to lie entirely within Menghe, but because much of its course runs through semi-arid terrain, its discharge rate at the mouth is only 11,540 cubic meters per second, including water from Polvokian tributaries that join near the mouth. The White River originates in the Chŏnsan mountains, and for some time runs in a valley parallel to their peaks, before turning northward through Sanhu province and then running east toward the East Menghe Sea. Along the final 1,121 kilometers of its length, the White River delineates Menghe's border with Polvokia.

Along its central course, roughly from the city of Ryŏjin to the Polvokian border, the White River carves canyons and gorges through the soft sandstone rock. Next to the city of Hapsŏng, it plunges sharply in the Great Northern Waterfall. Both the waterfall and the canyons around it are popular sights for tourists, drawing millions of visitors every year.

During several dynasties, the middle stretch of the White River defined Menghe's frontier with the Central Hemithean nomads. Its waterfalls and rapids made it an unreliable shipping route, and in most winters it froze over in large sections, allowing nomadic invaders to cross on horseback. Fortresses, watchposts, and walls on the southern bank were necessary to bolster its natural defenses. The northern province of Gangbuk (강북 / 江北), meaning "north of the river," was incorporated during the Myŏn dynasty after a war with the East Dzungar tribes, and its own northern border was a subject of dispute with Polvokia until 1937.

Canals

Because river barges were the most efficient method for transporting passengers and bulk goods before the introduction of the railroad, engineers in Imperial Menghe expended great effort to make tributary rivers navigable, building dams, weirs, and locks to help barges move upstream.

The highest culmination of this effort came in large-scale projects to link different river systems through manmade canals. These revolutionized early transport by allowing barges to more easily move around the country, and were particularly important in ferrying tribute and bulk trade goods between the Imperial capital, usually located on the Meng river, and cities elsewhere in the country.

Two Rivers Canal

The Two Rivers Canal lies in Hasŏ province, where it links the Min River, a tributary of the Ro, with the Punsu river, a tributary of the Meng. The excavated canal itself is only 44 kilometers long and crosses fairly level terrain, with no weirs, locks, or elevation changes. The main engineering challenge in its construction was the broader water management system needed to make the passage navigable for barges. Both the upper Ro and the upper Punsu were widened, straightened, and deepened, with work teams dredging out sediment into embankments on either side. A permanent connection between Lake Tae and the upper Min, with floodgates on its upper course, allowed the vast lake to be used as a storage reservoir, reducing flood risks in the summer and providing a steady supply of water in the dry season. When altered sections of river are included, the canal is 276 kilometers long.

The core components of the Two Rivers Canal were built at the height of the Meng Dynasty under Emperor Mu Je, who used the new connection to pull the newly acquired Chŏllo plain into Menghe's economic orbit. Over the centuries that followed, it would be regularly repaired, reinforced, and expanded, with special attention to the water management system feeding it. Today it remains a strategic route for barges and watercraft, and is particularly attractive for its lack of lock gates south of Lake Tae.

Grand Gangwŏn Canal

The Grand Gangwŏn Canal was built later, under the Sung dynasty, though attempts at digging it began under the Meng and Kang. It links the Jade River in Ryŏngsan with the Anchun river in Gangwŏn, and lies directly on the present Ryŏngsan-Gangwŏn border. Though the Jade river is shorter than the Ro, and was only navigable out to two cities, Yŏngjŏng and Ranju, it provided a direct shipping route from Hwasŏng to the East Menghe Sea. This helped integrate the Donghae region into Menghean water trade, avoiding the long and hazardous route along the Ryŏngsan coast.

The Grand Gangwŏn canal required only five and a half kilometers of digging, but it ran over much more challenging terrain. Though it began at the least challenging curve along the Jade river's bank, it required engineers to dig the initial spillway through solid rock, in some places twenty meters deep. The canal's remaining stretch, 41 kilometers long, mostly followed the course of a stream winding through the valleys, but had to be widened and reinforced to handle the large inflow of water from the Jade. Due to the 76-meter elevation difference between the two rivers at the connection points, the canal required a series of pound locks, among the first in the world at the time.