Achra

Achra is a region in central Charnea north of the eastern Agala range and south of the Erg Awakar. The region is defined by a major geological depression at the base of the central Scipian drainage basin that serves the endpoint of many ephemeral watercourses as well as the perennial Iza river and its large inland delta. Achra is rich in vital resources including groundwater reserves, arable land, and deposits of petroleum, copper, and other minerals of importance to local and international industries. It is the wealthiest and most developed region of Charnea, contributing more than two thirds of all economic activity in the country and playing host to the national capital Agnannet. Achra is the hub of the historical trans-Scipian trade routes and the modern Ninvite railroad, occupying a central position in the networks of Scipian overland commerce since ancient times. The region was the center of power for the proto-Charnean Ihemodian Empire and the homeland of multiple pre-Ihemodian civilizations with a history and cultural heritage stretching back to the Ninvite bronze age and some of the first agricultural societies on the continent. Achra is known as the "Beating Heart of the Ninva" because of its great importance to the modern and historical desert-dwelling civilizations of the greater Ninva.

Geography

The Achra depression is a structural foreland basin formed by the same geologic processes responsible for the uplift of the eastern Agala highlands. The trough in which Achra sits runs along a northeast-southwest axis parallel to the orientation of the highlands, becoming wider toward the north. Achra is the deepest and second largest of the many depressions of the Ninva desert that drop below sea level, covering an area of 55,000 square kilometers at an average elevation of 55 meters below sea level. The slope of this depression is steepest along the southern edge where Achra abuts with the foothills of the Agala rising sharply from the floor of the Ninvite plain, whole northern Achra is flatter and has a gentler incline as the landscape drops below sea level into the depression. Achra sits both in the geographic center and at the lowest point of a major drainage basin defined to the south by the Agala, to the east by the Adjer range, to the west by the Arwa, and to the north by the Adrasic and Arkelbi mountains in Talahara and Tyreseia. Ephemeral streams and rivers fed by the sporadic showers of the Ninvite wet season as well as the floodwaters produced by the west Scipian monsoon rains on the slopes of the Agala terminate in the Achra depression. Southern Achra is marked by a landscape of canyons, ravines and badlands as the pre-historic watercourses eroded the sedimentary rocks along the southern slopes. These patterns of erosion are much less prevalent in northern Achra, where shallow channels carry the waters of the sporadic Ninvite rains for only a few days or even hours out of the year during brief but intense flash-floods.

The Iza river, one of only three permanent rivers anywhere in the Ninva, flows north from the central Agala into Achra where it spreads out across the floor of the depression creating the Iza delta. Floodwaters from the monsoon reach the delta every year around the month of July, spreading across the floodplains of southern Achra and generally reaching a maximum extent in August before gradually receding towards the end of September as water is lost to evaporation and infiltration into the underground aquifer. The physical extent of the Iza delta therefore fluctuates significantly according to the timing and intensity of the monsoon rains supplying its headqaters in the Agala, with a minimum extent of under 2,500 square kilometers and a maximum recorded extent of 14,600 square kilometers. Central Achra is home to many chott salt lakes and salt marshes that occur along the edges of the Iza delta that only receive inflows of fresh water at the peak of the flood season. Most of the floodwater evaporates over the dry season leaving behind brackish and more concentrated salt water in low-lying areas, and dried out salt pans in others. The largest such body of water is the Chott Achra salt lake for which the region is named, located southwest of the city of Asihar along the northern edge of the Iza delta's maximum extent.

The geology of the Achra depression is predominantly sedimentary, consisting mainly of the common Ninvite sandstone bedrock. The grain of this stone, formed from wind-swept dunes compacted into rock over millennia, is highly porous and permeable to groundwater. The Ninvite Sandstone Aquifer lies within the bedrock under Achra. This aquifer is only a few meters below the surface in the deepest parts of the Achra depression, contrasting with its depth of over 100 meters in most regions of the central Ninva. The infiltration of Iza floodwaters into the sandstone accounts for virtually all of the yearly regeneration of groundwater in the Ninvite Sandstone Aquifer. The permeability of the sandstone bedrock is significantly reduced in two areas of Achra by the presence of major igneous intrusions. The smallest of these is the highly eroded igneous dome on which the city of Agnannet is built, with the larger introsion found under the eastern half of the depression.

Natural resources

The igneous formation found underneath eastern Achra hosts two major porphyry orebodies of hydrothermal origin. These are rich in copper but also contain significant deposits of gold and minor deposits of silver, together with small amounts of molybdenum. All of these minerals are produced by the same geologic process and occur together within the porphyry formations in east Achra. The exploitation of these formations dates to prehistory but was historically limited because of the great difficulty in the excavation of the main deposits which are found deep underground. The modern mines in these areas extend many hundreds of meters underground and consist several kilometers of tunnels and shafts, many of which would not be survivable for workers without modern equipment. Petroleum can be extracted in several places in the Achra depression. The origin of these reserves can be traced to algal growth in the pre-historic Achra Sea, an inland body of water that once filled the depression many millions of years ago and left behind carbonate layers underneath the sandstone bedrock. Exploitation of these horizons peaked in the 1950s but has since reduced due to the high cost of operating the deep wells as well as disastrous effects of groundwater contamination caused by petroleum extraction leading to infiltration of pollutants into the groundwater.

Water is by far the most vital resource that Achra offers in abundance in stark contrast to the surrounding Ninva. While the yearly flooding of the Iza delta and its importance to agriculture is the most visible form of Achra's water resources, it is in fact the Ninvite Sandstone Aquifer that represents the most important reservoir for the economy of the local area. Extraction from the aquifer in Achra is much more economical due to its close proximity to the surface, enabling large volumes of groundwater to be drawn for agricultural and industrial purposes as well as personal consumption year-round. In many cases, excavation required for extraction of water can even be done by hand, in stark contrast to the deep drilling technology that must be used to dig wells over 100 meters deep across most of the Ninva. It is this water and not the Iza floodwater that enables the enormous urban zones to persist in Achra despite negligible rainfall.

Achra Triangle

The urbanized zone in the Achra depression is concentrated in the center and south of the region, defined by the three large metropolises that sit on the valley floor. The largest of these is Agnannet, whose municipal core has a population of 3 million with an additional 4 million inhabiting its 17 suburbs. To the east of Agnannet, sitting on what once was the northeast shore of Chott Achra, is Asihar, with a total population of 1.2 million including its suburbs. The smallest of the three is Atafala located south of Agnannet, along the junction of the Iza delta's main channels. The population of Atafala is 250,000. Together, these three cities and the extensive urban corridors that link them are known as the Achra Triangle megacity, a conurbation with a population of 11.2 million. The Achra Triangle is highly urbanized and concentrated in terms of its population, with 3 out of every 4 residents living in one of the three main cities of the Triangle or their direct suburbs at an average population density of 14,000 people per square kilometer. The remaining population outside of the main cities and their suburbs inhabit over 150 towns found in and around the Iza delta along the road and rail corridors that link the three points of the Triangle.

Responsibility for the planning and maintenance of the extensive regional infrastructure required to sustain the Achra Triangle falls under the auspices of the powerful Achra TET office, an organ funded by the national government in Agnannet to oversee all regional development projects within the Achra depression with a particular focus on the development of the capital and the wider urban zone of the Triangle. Meeting the transportation needs of the Triangle has been the main focus of the Achra TET since its inception, although the organization is also responsible for overseeing flood control projects in the Iza delta as well as the management of the local sector of the national power grid, including all 24 power plants and solar fields in Achra.