Beauchastel is located some 10 km south by south-west of
Valence and 20 km north-east of
Privas. Access to the commune is by the D86 road from
Charmes-sur-Rhône in the north which passes through the commune and continues south to
La Voulte-sur-Rhône. The D86E branches from the D86 at the northern communal border and goes to the town then continues south to rejoin the D86 at La Voulte-sur-Rhône. The D21 goes west from the town to
Saint-Laurent-du-Pape. The east of the commune includes a portion of the
Île Saint-Thimé in the
Rhône river which is also the departmental border with
Drôme. A railway line from
Saint-Péray in the north to La Voulte-sur-Rhône in the south passes through the commune but there is no station in the commune. The commune consists of a large urban area along the banks of the Rhône with farmland south of the Eyrieux and forested hills for the rest. A branch of the
Rhône forms the eastern border of the commune with the main branch flowing south through the commune and continuing to eventually joining the sea at
Port-Saint-Louis-du-Rhone. The
Eyrieux river flows through the commune from the west to join the Rhône just south of the commune. Numerous streams rise in the commune and flow south to feed the Eyrieux including the
Ruiseeau de Thouac (which forms the western border of the commune), the ''Ruisseau d'Abrou
, and the Ruisseau de Chauvert
. The Ruisseau de Feuillas
flows east through the north of the commune to join the Rhône. There is a dam on the main branch of the Rhône with an electricity generating station: the Centrale Electrique de Beauchastel''. Beauchastel was often the victim of floods of the Eyrieux, until the construction of a damin the upper reaches of the river in 1860. ==Toponymy==