Characteristics of Irrigation Return Flow in a Reservoir Irrigated District

Abstract

The objective of this study was to investigate characteristics of irrigation return flow from paddy block in a reservoir irrigated district during growing seasons. The irrigation return flow was divided into three parts, quick return flow from irrigation canal (RFI), quick return flow from drainage canal (RFD), and delayed return flow (DRF). The RFI was calculated from water level and stage-discharge relationships at the ends of the irrigation canals. The DRF was estimated using measured infiltration amount from paddy fields of the irrigated district. A combined monitoring and modeling method was used to estimate the RFD by subtracting surface runoff from surface drainage. The paddy block irrigated from the Idong reservoir was selected to study the irrigation return flow components. The results showed that daily agricultural water supply (AWS), the RFI, and the RFD were 27.4 mm day , respectively in May, which were greater than other months (p<0.05). The return flow ratio of the RFI and the RFD were the greatest in July (34.6%) and May (72.3%), respectively. The daily AWS was closely correlated with the RFD (correlation coefficients of 0.76~0.86) in except for July with, while correlation coefficient with the RFI were 0.56 and 0.42 in June and July, respectively (p<0.01). The total irrigation return flow was 1,965 mm in 2011, and 1,588 mm in 2012, resulting in total return flow ratio of 84.6% and 79.1%, respectively. This results indicate that substantial amounts of agricultural water were returned to streams as irrigation return flow. Thus, irrigation return flow should be fully considered into the agricultural water resources planning in Korea.

Uncertainty in Irrigation Return Flow Estimation: Comparing Conceptual and Physically-Based Parameterization Approaches

“…At the paddy block scale, the components of surface water draining out of the main outlet can be expressed as: (4) where is total surface drainage in a paddy block (mm); is paddy field drainage (mm) that is excess water discharged from paddy fields and collected in the drainage ditch ( Figure 1); and is the time step (day). In a modeling approach, can be simulated as a fraction of [5,6,8,15]: ( 5) where is the delivery management coefficient (fraction); and represents a year. It has been reported that varies depending on farming practices and weather conditions [5,8,15].…”

“…Irrigation water supplied from sources such as reservoirs, pumping stations, and tube wells may not be consumed in plots and rather may directly discharge into drainage canals and downstream streams. Such water is known as irrigation return flow (RF), affecting the flow regime of the downstream rivers [1][2][3][4][5][6]. RF is an important part of the water balance of a watershed and a critical factor requiring consideration when developing water resources management plans and practices, determining the operation rule of irrigation systems, and assessing environmental water use [7][8][9].…”

“…Previous studies have estimated RF by measuring the amount of water irrigated, infiltrated, and drained during the nonrainy season, assuming that RF should be negligible during rainy days [12][13][14]. However, other studies have reported that a large amount of RF may discharge into rivers during rainy days from watersheds in which irrigation water is heavily used [6,8,15]. Such a finding suggests that for accurate RF estimation, routing processes of irrigation water in an extensively irrigated watershed should not be ignored on…”

Simulation of Agricultural Water Supply Considering Yearly Variation of Irrigation Efficiency

“…서 론 농업용수 공급량(agricultural water supply)은 관리자 가 수리시설물에서 관개지구로 실제로 공급하는 용수량을 의미하며 농경지에서 작물재배를 위해 이용되는 필요수량 (irrigation water requirement), 수로에서 손실되는 송수 손실 수량(conveyance loss), 그리고 포장으로 유입되지 않고 하천으로 직접 회귀하는 배분관리 용수량(delivery management water requirement)을 포함한다 Song et al, 2015).…”

“…농업용 저수지는 관개 후 수위가 내려가고, 상류유 역의 유출량이 유입되어 다시 수위가 상승한다. 저수지 하류 관개지구로 공급된 용수량은 전량 작물에 의해 소비 되는 것이 아니며, 약 32∼86%가 포장에서 소비되지 않고 하천으로 회귀되어 하천유량을 구성하는 중요 성분이 된 다 (Song et al, 2015). 이와 같이 농업용수 공급은 관개지 구의 수문 순환과 비관개지구의 수문 순환, 그리고 수리 시설물의 저수량 등과 복합적으로 연계되어 상·하류의 하 천 유황에 영향을 미친다.…”