Ħarq Ħammiem valley is situated between the Local Councils of St. Julians and Pembroke. Formerly part of a much wider system that extended up to Wied Mejxu, this remnant valley is popularly and mistakenly associated with just the central area characterized by the relatively steep rocky terrain and meandering geomorphology. However, as in the case of many valley systems, this valley also includes arable land in this case along its upper reaches. These fields are important from a geomorphological as well as hydrological perspective. The upper reaches also contain a now-artificial water channel. Run-off storm water from the Pembroke–Swieqi conurbation passes along this channel and into the central part of the valley, eventually discharging into St.Julians Bay.
The remnant valley system also includes the entrance to Ħarq Ħammiem cave along its lower valley side. The lower reaches of the valley and much of its former extent has been engulfed by urban development.
The central area still sustains rare species of plants with a restricted distribution in the Maltese Islands, including:
crested dock (Rumex cristatus);
cage thistle (Atractylis cancellata);
hairy plantain (Plantago bellardi);
tooth-leaved club-moss (Selaginella denticulata);
Sicilian squill (Scilla sicula).
MEPA scheduled the remaining extent of Ħarq Ħammiem valley system as an Area of Ecological Importance and Site of Scientific Importance as per Government Notice No. 370/08 in the Government Gazette dated 23 April 2008.