Ambica River is one of the important west flowing rivers with its catchment in Gujarat and Maharashtra. The Ambica basin which is adjacent to the Auranga basin can be divided in to two prominent physiographic zones. The eastern part comes under a rugged mountain chain of the Sahyadri Western Ghats and descending on the western side to the edge of the uplands of Surat district. This region is situated at general elevation ranging from 1050 m to 100 m. The western part consists of hills and valleys which generally lie below 100 m elevation.

It originates from Saputara Hill ranges near village Kotambi of Surgana taluka in the Nasik district of Maharashtra. After flowing for a length of 136 km it drains in to the Arabian Sea. The important tributaries of the Ambica River are Kapri, Wallan, Kaveri and Kharera. The river Ambica basin lies between 20° 31’ and 20° 57’ North latitude and 72° 48’ and 73° 52’ East longitude with a drainage area of 2715 Sq.km. The Valsad, Dangs and Surat Districts of Gujarat and a small portion of the Nasik district of Maharashtra falls in the basin. There is only one H.O station of CWC at Gadat in Ambika basin.

Accordingly to Koeppan’s Scheme, the climate of the basin is classified as AWTropical Savannah, as most of the peninsular plateau, south of Tropic of Cancer, is classified. In the initial reaches, the climate is influenced by the Western Ghats which gradually changes as the river reaches the coastal plains. The climatic variations are experienced in the patterns of temperature, rainfall & winds, rhythm of seasons and degree of wetness or dryness. These are described as follows:

The Temperature is maximum in the month of May and Minimum in the month of December to January. The maximum, minimum temperatures observed vary from 27.4°C to 40°C and 28.6°C to 8° C respectively.

The basin receives most of the rainfall from the South West monsoon from June to September. Average annual rainfall in the basin is 1719.1 mm.

The average monthly wind speed varies from 0.3 km/h to 2.5 km/h. In the pre and post-monsoon period, the wind speed is generally higher. The pre dominant wind direction is NE.

The relative Humidity in Ambica basin varies between 93.3 % to 82.0 % depending upon the season the humidity is naturally maximum in the monsoon period and is around 93.3 to 89.9 %. In the winter months of November and December the relative humidity comes down.

The basin can be divided into two prominent physiographic zones. The eastern part comes under rugged mountain chains of the Saputara Hills and descends on the western side to the edge of the uplands of Surat district. This region is placed at a general elevation of 1050 m to 100 m. The western part, barring the coastal plain, is essentially in the sub Sahyadrin zone of hills and valleys generally below 100 m elevation. Deccan traps and intermediate amphitheatres have developed out of the alluvial debris washed from the hills. The lower reaches of the basin upto the coastal margins are mainly alluvial plains.

Soil of Ambica basin can be broadly classified into three group viz. Laterite soil, deep black soil and alluvial soil.

Water Year Book 2013-2014, West Flowing Rivers, CWC, Narmada and Tapi Basin Organization, Hydrological Observation Circle, Gandhinagar, March 2015.