The rivers of Afghānistān flow into the three basins of the Indus, the Helmand and the mū Daryā. The region from which the main ones depart is in the Kōh-i Bābā; the watershed between the non-drainage region and the peripheral one proceeds along the crest of the Hindū Kush, passes W on the Kōh-i Bābā, continues in the direction of S. and SE. along the central Afghānistān range, and continues with Sefīd Kōh.
The Kābul originates at the Unai pass, on the SE slopes. of the Kōh-i Bābā, it leaves Gelālābād on the right, crosses the Khaibar pass, and flows into the Indus near Attock. It has a path of about 500 km., And receives the waters of the southern slopes of the Hindū Kush on the left, and the northern watershed of the Sefīd-Kōh on the right. Among its tributaries are to be mentioned: on the left the Tagāo, which rises from the Hindū Kush to N., the Lōghar da S. (militarily important where it crosses the Ghaznī-Kābul road), the Bara, which rises in the Afrīdī region, the Swāt, the Panǵshīr, the Alishang and the Kunar, which originate in the Kāfiristān; on the right the Kābul receives only the Surkh-rūd. These rivers, although of limited volume, collect the waters of very large regions, and mark important military and commercial routes between India and the plateau. For Afghanistan 2006, please check computergees.com.
The Helmand (Haetumat dell’Avesta, Gr. Etymandros or Erymanthos) rises along the Kābul, flows towards the SW. up to 180 km. about below Girishk, then turns W, and after a 115 km. in this direction, to the NW, and flows into Lake Sīstān. Its entire course is about 1200 km. After Girishk it is navigable. It is widely used for irrigation. Its left tributary, the Arghandāb (Avesta Harawaiti, Gr. Arachotis), has numerous tributaries: Tarnak, Arghāsan, Dori and Lora. Other rivers to the East. del Helmand, which follow the same direction, are: the Kash-rūd, the Farāh-rūd and the Harūt-rūd.
The mū Daryā group includes the Murghāb and the Harī-rūd. The Āmū Daryā (Oxus), which was born in the Pāmir plateau, with the name of Pangiah, marks the N. and NE border. of Afghānistān for a 500 km. The Harī-rūd rises from the southern slopes of the Kōh-i Siyāh, at 34 ° 30 ′ lat. and the 67 ° of long., and turning to the West it passes to S. of Herāt. Just below this elbow it turns to N., leaves the Afghan territory near the northernmost branch of the Paropamiso, and turning again to the NE., It divides into two branches, and gets lost in the swamps of Russian Turkestan. Herāt and its valley are irrigated by canals from the Harī-rūd. In summer its waters are very scarce. It has only one important tributary, the Tagāo-Ishlan. Between Āhenghirān and Khaussi it crosses an inaccessible gorge, with walls that drop steeply for a hundred meters.
Lake Hāmūn, in Sīstān, receives the waters of the Helmand, Farāh, Kushk and Harūd rivers from the Naizar lagoon during flood periods. It is partly in the Afghan territory, partly in the Persian one. Its waters, very slightly salty, are drinkable. Its basin, which is not very extensive in lean periods, widens enormously in the S. direction when the rivers are in flood, reaching an extension of 20 km. for 150, and then pours into the depression called Gōd-i Zireh; this happens approximately every ten years.
The main natural subdivisions are three: the central mountainous region, which occupies most of the country, the southern region, of steppes and deserts, the northern one (Afghan Turkestān) made up of steppes, hills and mountains, crossed by fertile valleys.
The mountainous region is divided into four parts: a) Hazāra (see) plateau of central Afghānistān; b) Hindū Kugh, Paropamiso and Kōh-i Bābā; c) region of Kābul (v.), Kāfiristān (v.) and Sefīd Kōh; d) Indo-Afghan and Belūcistān chains. The plain of Turkestān (ancient Bactria) is not very high; the capital, Mazār-i Sherīf, is 377 meters above sea level; its rivers, Sangalak, Ister, Balkhāb, Khulm, are lost in the sands before reaching the mū Daryā, forming unhealthy swamps. The southern region, close to the Persian border, is divided by Helmand into two desert zones: Sīstān to the West and Registān to E., of about 150,000 sq km. altogether.