### Simplified drain-spacingcomputation method to reduce groundwater table

Suny Sunyoto

Thursday 2 july 2015

17:00 - 17:15h at Oceania Foyer (level 0)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology

Parallel session: 13L. Water resources - Flow interactions

A great deal of this research work has been carried out in developing a computation method which is simple and reliable for drain spacing formula. The common practice for controlling the ground water table was using an open ditches system. Recently, modern agriculture has not used these systems and it was replaced by pipe drains. Hooghoudt developed a technique to compute the space between pipe drainage using a combination of tables and equation. Other researchers improved this technique of computation using graphics and equations. This paper attempted to find a simple technique of computation for drains spacing using equations without tables or graphics. The result of computation with the equal data shows a marginal deviation to the existing methods about 5 % for the 20 cm diameter of pipe as a computation standard in this example. Some executions can’t be done by existing methods for these some example data, like Hooghoudt’s solution by table method due to in this paper provided only table for ro = 0.10 m and Dagan method can only compute 0.05 m < ro < 0.15 m for this example data, and all of them can’t compute the drains dimension of ro=½b=½hw=0 m except the proposed methods. Hooghoudt’s solution by equation method is unreliable formula because the variation of ditch depth gives the constant drains spacing value and this method independent to the width of ditch base. Kirkham, Dagan and Ernst methods are more reliable because the variation of pipes or ditches dimensions show the various drain spacing value, even though the comparison results are not significant. The proposed methods are the most reliable than the others because the variation of pipes or ditches dimensions of drains gives the realistic value of drain spacing results. The of proposed methods using equations without trial and error steps, nor graphic, nor table, thus it is easier to be conducted and it can be considered as method of drain spacing computation. Keywords: Drain spacing, groundwater level, graphic, table, equation