The Dau River
Large arterial river running the length of the South Western Inland Region.
Sections
- Overview
- Etymology
- Dau River Sections
- Source (Zone 1)
- Western Kuha Steppe (Zone 2)
- South Western Inland Region Mediterranean Plateau (Zone 3)
- The Escarpment (Zone 4)
- The Dau Delta (Zone 5)
- Summary of flood pulse periods
Overview
The Dau is a large river that flows roughly from north to south-west at a length of around 3,200kms. Its headwaters lie in the North Western Tundra Belt (NWTB) at approximately 49.3°N, while it terminates at the southern coast of Kuha around 32°N. The Dau River spans four distinct climate zones totalling a drainage basin of roughly 1,946,000 km². It begins as a small stream in the tundra formed by snow melt from its headwaters, with major contributions to the flow from the snowmelt of the tundra region. As it flows southwards, the Dau braids through the Western Kuha Steppe and transforms into a meandering plateau river, travelling through arid steppe land and into a mediterranean climate plateau. Finally in the last 90km before termination, the river travels through a gorge corridor before spilling out into lowland valley terrain reaching sea level. The final terminus is the dynamic Dau delta that transitions into the sea. All these characteristics makes the Dau River the largest and most culturally consequential river of Western Kuha.
| Parameter | Value |
|---|---|
| Total length | 3,200km |
| Basin area | 1,946,000 km² |
| Mean annual discharge | ~8,000 m³/s |
| Peak discharge (primary flood) | 35,000–42,000 m³/s |
| Primary flood months | M6-M7 |
| Sediment load | ~150 Mt/yr |
| Source elevation | ~2,500m |
| Source latitude | ~49.3°N |
| Terminus latitude | ~32°N |
Etymology
The word dau means “mother” in many of the Southern SWI languages that were spoken in the [[## Southern Intermontane Basin|Southern Intermontane Basin]] around 4000 TOR. Some documentation refers to the Dau River as the Kohoni Dau which can be translated as “the Regal Mother”. Given the transparency of this meaning of dau to Southern SWI language speakers, the Northern SWI speakers call the river ndawo ongo, “mother river”, or further contracted as ndawongo.
The residents of the Dau Delta refer to the Dau coloquially as danmene “the big one”. The various tribes of the Dau Delta are each said to have a “true name” for the river, but these names are very rarely uttered. They fear this would be interpreted as presumptuous by the mighty river, resulting in violent flooding or the withdrawal of its life supporting flow during summer.
Dau River Sections
The Dau River passes through five regions. These regions are roughly defined by regional precipitation and terrain elevation.
Beginning from its headwaters, the Dau regions form north to south are as follows:
- Source: North Western Tundra Belt (Zone 1)
- Western Kuha Steppe (Zone 2)
- South Western Inland Region Mediterranean Plateau (Zone 3)
- The Escarpment (Zone 4)
- The Dau Delta (Zone 5)
Source: North Western Tubdra Belt (Zone 1)
The majority of the Dau’s water flow is sourced from the cluster of mountains called Sogum, and the tundra plateau itself. Some 80% of the Dau’s waters originate from these two sources.
The headwaters of the Dau technically begin at Sogum. The Sogum lie at a latitude of approximately 49.3°N, reaching elevations of 2000-2500m. The annual temperature range of these mountains is around −7 to −9°C (summer-winter). Only three out of the 14 months of the year have a minimum temperature above 0°. The Dau River is therefore ice-locked for the entire winter season (late M13 through mid-M3), but it starts to melt once mean temperatures start passing 0°. In the Sogum mountains this snow-melt begins in early to mid-M6, with the melt peaking at the beginning to middle of M7 (early summer).
While to Sogum are the technical headwaters of the Dau, the bulk of its water is produced by the ice-sheet snow melt of the North Western Tundra Belt. The permafrost of this plateau at elevations 1000-1500m start melting in late M5, early M6 when mean temperatures rise above 0°. This is earlier than the melting season on the Sogum by a near full-month. Due to the permafrost freezing the lower reaches of the soil in the tundra, snow melt water is mostly unabsorbed and runs off straight into the tributaries of the Dau.
The difference in timing of snow-melt means there are two melt pulses: one in late M5 from the plateau melt, and one in mid-M6 from the Sogum snow melt. The contribution of water to the Dau is significant, resulting the Dau River experiencing two distinct flooding seasons down its entire length.
| Parameter | Value |
|---|---|
| Length | 576km (18% of total) |
| Latitude | ~49.3°N → ~42°N |
| Elevation | ~2,500m → ~1,200m |
| Climate | ET / ET-EF margin |
| Annual Mean Temperature | -1°C (winter mean -15°C; summer mean 10°C) |
| Terrain | Highland tundra |
| Primary flow peak month | Late M5 |
| Secondary flow peak month | Early to mid-M6 |
[[Western Kuha Steppe]] (Zone 2)
The majority of the Dau’s flow-path is through cold arid steppe region. The steppe plateau soil provides adequate drainage, with the river producing an overall braided and meandering shape. Unlike in the tundra region, the Dau River flows year-round, though the flow in winter is significantly weaker.
The two flood pulses in spring time transform the landscape around the Dau drastically. The first pulse arrives in early M6, and the second pulse in the middle to later parts of M6. The flood pulses widen the active channel of the river between 5 to 20kms. When including the wider flood plains, the area can be inundated between 10 to 20km on either side of the channels. In the northern part of the river the flowing results in the re-arrangement of channels, making the landscape highly dynamic. The deposited sediment is mostly gravel. Overall, travel around the Dau River in the steppe region is challenging in spring.
| Parameter | Value |
|---|---|
| Length | 1,024km (32% of total) |
| Latitude | ~42°N → ~36°N |
| Elevation | ~1,200m (plateau surface) |
| Climate | BSk (cold semi-arid steppe) |
| Annual Mean Temperature | 5°C (winter mean -9°C; summer mean 16°C) |
| Terrain | Broad basaltic plateau |
| Primary flow peak month | Early M6 |
| Secondary flow peak month | Mid to late-M6 |
SWIR Mediterranean Plateau (Zone 3)
Entering the mediterranean plateau, the Dau River continues to meander in a south-westerly direction. With well-defined flood-plains on either side, the river width is between 200 to 500m with the flood plains extending a further 5 to 15km depending on the location. When the flood pulses arrive in mid to late M6, the entire flood plain becomes inundated. The pulse can last 2-3 days. Since the flood is sources from now melt, the water is cold and may retain ice floes.
As the land transitions between the arid cold steppe to a mediterranean climate, winter rainfalls start contributing to the flow of the Dau River. There is enough sustained precipitation during the winter, that most years see minor floods about once a month. In scale, these are more benign and gradual in comparison to the spring flood pulses, lasting anywhere between 3 to 7 days.
| Parameter | Value |
|---|---|
| Length | 704km (22% of total) |
| Latitude | ~36°N → ~34°N |
| Elevation | ~1,200m → sea level |
| Climate | Csb (plateau) → Csa (gorge base) |
| Temperature | |
| Terrain | Mediterranean plateau → gorge descent → delta approach |
| Primary flow peak month | Mid-M6 |
| Secondary flow peak month | Late-M6, early M7 |
The Escarpment (Zone 4)
With an elevation change from around 1000m to 500m over a 90km distance (mean gradient of approximately 0.76°), the Dau River etches its behaviour onto the SWIR Escarpment’s landscape.
At the beginning of the escarpment there are steep gorges where the Dau is confined to narrow channels. The arrival of the flood pulses may coincide with the summer solstice. The high levels of discharge that is channelled into the narrow gorge makes the water levels rise drastically, and travel is extremely dangerous at this time of the year. Once the gorge gives way to the broader valley, the water spills out into meandering channels, eventually forming the apex of the Dau Delta.
| Parameter | Value |
|---|---|
| Length | 704km (22% of total) |
| Latitude | ~34°N → ~32°N |
| Elevation | ~1,200m → 500m |
| Climate | Warm summer mediterranean climate (Csb) ~ Hot summer mediterranean climate (Csa) |
| Temperature | At the gorge: winter 4°C; summer 24°C) Valley: |
| Terrain | Mediterranean plateau → gorge descent → delta approach |
| Primary flow peak month | Mid-M6 |
| Secondary flow peak month | Late-M6, early M7 |
The Dau Delta (Zone 5)
The Dau Delta is the terminus of the Dau River. At latitude around 32°N, it is a hot mediterranean climate area along the southern coast of Kuha. By the time the Dau has run its corse at the delta, the sediment is mostly a fine silt and clay composition.
Given that the Dau Delta is entirely shaped by the hydrology of the Dau River, see the Dau Delta Section for further details.
| Parameter | Value |
|---|---|
| Latitude | ~32°N |
| Elevation | Essentially sea level |
| Climate | Hot summer mediterranean climate (Csa) |
| Temperature | Annual mean 19°C (winter 11°C; summer 26°C) |
| Terrain | Mediterranean plateau → gorge descent → delta approach |
| Primary flow peak month | Mid-M6 |
| Secondary flow peak month | Late-M6, early M7 |
Summary of flood pulse periods
The snow melts in the Northern Western Tundra Belt peaks in late M5, which is the main source that triggers the beginning of the Dau River summer flood. The snow melt of the actual river source, the Sogum mountains, contributes a more modest flow of water, beginning a secondary flood
| Location | Zone | Travel time | Primary peak arrival | Secondary (Mtns S) arrival |
|---|---|---|---|---|
| North Western Tundra Belt plateau | 1 | — | Early-mid M6 | |
| Sogum Mountains | 1 | — | Late M5 | |
| Western Kuha Steppe (northern extent) | 2 | ~3–4 days | Early M6 | Mid M6 |
| Mediterranean Plateau (northern extent) | 3 | ~9–10 days | Mid M6 | Late M6 |
| The Escarpment | 4 | ~12–13 days | Mid M6 | Late M6–early M7 |
| Delta apex | 5 | ~13–14 days | Mid M6 | Late M6–early M7 |