ارزيابي روش هاي تجربي تعيين نشت در كانال هاي خاكي (مطالعه موردي: دشت قزوين)

Evaluation of empirical equations of seepage estimation from earthen canals

تلفات نشت از كانال هاي خاكي سهم زيادي در تلفات آب در بخش كشاورزي دارد. در اكثر شبكه هاي آبياري كشور از معادلات تجربي براي تعيين نشت استفاده مي شود. در اين مطالعه دقت معادلات تجربي اينگهام، ديويس و ويلسون، موريتس، مولس ورث و يني دوميا و روش ميسرا نسبت به روش آب ايستي در سه كانال در دشت قزوين، ارزيابي شد. نرخ نشت به روش آب ايستي در كانال‌هاي 1، 2 و 3 به‌ترتيب 9/167، 5/572 و 5/379 ميلي‌متر در روز اندازه گيري شد و در بين روش هاي تجربي روش‌هاي ميسرا و موريتس دقت قابل قبولي در تخمين نشت در منطقه مطالعه داشته اند و توصيه مي شود در اين منطقه از اين دو روش استفاده شود.

There is a need for proper water demand management since water scarcity is a fact in Iran due to the arid nature of the region. Seepage losses constitute the large amount of losses in agriculture. In some cases, the rising of underground water levels in adjacent lands to irrigation canal cause drainage and salinity problems for surface layers of soil.Therefore, it is important to find ways to limit losses through seepage. In Iran, empirical equations are mostly used to determine seepage in unlined channels in the most of the irrigation networks. In this study, the seepage losses in three earthen canals in Gazvin plain were determined by Ponding Test method and also the empirical equations were used to estimate the rate of seepage losses in these canals. Empirical equations such as Ingham, Davis and Wilson, Moritz, Molesworth – Yennidumia and Misra were evaluated with Ponding Test. The seepage rates obtained by the ponding test on canals No. 1 to 3 were determined to be 163.6, 567.7 and 379.5, respectively. Among empirical equations, Misra and Moritz methods found to have acceptable precision for channel seepage determination at the study area. Hence, these two formulas are recommended to be used.