The main objective of this investigation is to study experimentally the water surface profiles and to obtain convenient expressions for the estimation of discharge coefficients (C d ) for free flow over chimney weir and the discharge factor (q/q 1 ) for submerged flow. Four chimney weir models with different vertex angles were constructed and tested, the surface water profiles, for all models were smooth upstream and fall suddenly downstream the model and at a high discharge it become concave

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... ile at law discharge the water surface profile become convex. The coefficient of discharge for free flow increase with the decrease of the upstream head and with the decrease of half vertex angle ( ). While the discharge factor for submerged flow increase with the decrease of the submergence ratio (h 2 /h 1 ). Two general expressions were optioned, one, for the estimation of C d with respect of (h/p),(w/p) and for free flow conditions and the other for estimation of the coefficient factor (q/q 1 ) with respect to (h 2 /h 1 ) and (h 1 /p). /