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

Aerial view of the upper Iza delta

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.

Shore of the Chott Achra

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

Underground passage in a porphyry copper mine, east Achra

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.

Achra TET

The Achra Tanhet Edagg Tɑbennɑwt or Achra TET is the organ responsible for the development of the Achra Triangle.

Agriculture

Zezzeltaɤ canal, part of the irrigation network in the eastern Iza delta

The Iza delta is the breadbasket of Charnea thanks to its abundant supply of fresh water and the natural supply of nutrients found in the sediment carried by the Iza's floodwaters. Traditional agriculture in the delta historically involves planting crops in the fields immediately after the floodwaters recede in September and October of every year. Planting would occur while the ground was still moist and take advantage of the latent water left in the topsoil even after the open floodwaters have mostly evaporated away. This method took advantage of the natural sediments deposited by the flooding of the delta onto the fields, but would at times cause food shortages in years with severe floods that did not fully recede until late October and early November, delaying the planting season. Besides being limited to one planting per year by the natural rhythm of the Iza's flooding, the irrigation method of the traditional delta agriculture allowed most of the water to evaporate from the open fields with only that water which was retained between the particles of the topsoil actually being used by crops. The canalization of the Iza delta and complex network of dams and reservoirs created to tame the yearly flood between 1930 and 1965 greatly reduced the extent of the delta's flooding, and allowed the introduction of more efficient irrigation methods. Most modern farms in the delta use a variation of the drip irrigation techniques favored by the desert agriculturalists of the Ninva and are never intentionally allowed to flood. The use of drip irrigation enabled the same volume of crops to be grown with a much smaller amount of the Iza's yearly floodwater, in turn allowing for much of the flood to be diverted to new agricultural projects in previously uncultivated desert landscape across southern Achra, which together with the introduction of modern fertilizers dramatically increased the agricultural productivity of the region compared to that which was possible only two centuries ago.

The major Iza delta reservoirs, which are dug deep to maximize the volume of water for the same surface area, lose water to evaporation and infiltration through their concrete basins at a much slower rate than shallow floodwaters spread out across many square kilometers of open plains. Retaining floodwaters in this way makes the delivery of water for irrigation possible much later into the year than was previously possible, which reduces the amount of groundwater extracted every year for agriculture and allows for continuous irrigation for much of the year at reduced cost. The main drawback of the canalization and reservoir system in the Iza delta is the significant reduction in the natural nutrient rich sediments which were deposited on the farmer's fields by flooding in the past. This has partly been mitigated by the introduction of artificial fertilizers. In some cases, however, Iza delta farmers prefer to use mud collected from the canal and reservoir system to augment the productivity of their fields under the belief that the sediments confer the same bountiful fertility that the floodwaters did to their antecedents in previous centuries.

Mechanization of agriculture is more prevalent in the delta than elsewhere in Charnea, but remains relatively uncommon compared to what can be seen in the industrialized agricultural operations found in other countries. In most areas, particularly parts of Achra that were originally uncultivated desert, the method of closely packed companion planting typical of Ninvite agriculture remains predominant. This type of agroforestry which employs the use of shrubs and trees together with low-lying crops such as cereal grains is beneficial when it comes to the suppression of weeds and protecting crops from the damage that can be incurred by the wind and the sand it carries, presents a major barrier to the mechanization of most agricultural tasks. As a result, Achra remains in line with the wider Charnean trend of agriculture that is unusually manpower-intensive but in exchange is able to achieve a higher yield with a smaller land footprint and more efficient use of water.