The characterization of stormwater runoff from mix land-use catchments with an inadequate sewer network is a challenge. This study focused on characterizing stormwater runoff from the Paldang watershed area based on land-use type and sewer system coverage. A total of 76 sites were monitored during wet weather from seven different counties within Paldang watershed. Public sewer system (PSS) was installed at 48 sites, while 28 sites had no or individual sewer system (ISS) coverage. The results indicated that the sites included in the ISS group with higher forest and paddy land-use percentage exhibit higher values of average event mean concentrations (EMCs) and first flush intensity for suspended solids (SS), total nitrogen (TN), and total phosphorous (TP). In addition, upgrading runoff interception system can capture 59 % of the TP load in the first 43% of runoff within these sites. Similarly, rainfall depth and storm duration showed a positive correlation (R > 0.6) with nutrient loads within ISS group sites, as compared to PSS group. Therefore, these sites are likely to contribute higher TP and TN loads during heavier storm events and should be selected as priority management areas to combat the problem of eutrophication in Paldang reservoir.
토지이용이 혼재되고 하수관거 시스템이 미흡한 유역의 강우유출 특성을 파악하는 것은 매우 어렵다. 본 연구에서는 팔당호 유역에서 토지 이용 및 하수관거 형태에 따른 강우 유출 특성을 파악하고자 하였다. 이를 위해 팔당호 유역 7개 시·군에서 공공 하수관거 시스템 지역 48개소, 개인하수처리시설 지역 28개소에 대한 강우 유출수 모니터링을 실시하였다. 개인하수처리시설 지역의 토지 이용은 산림과 논의 비율이 높았으며 SS, TN, TP EMCs와 초기세척강도가 공공하수처리지역에 비해 높게 나타났다. 또한 초기 강우 차집 시스템을 설치하여 초기강우 유출수 43%를 처리할 경우 59%의 TP 유출부하량을 저감할 수 있을 것으로 기대된다. 개인하수처리시설이 설치된 지역에서 강우량 및 강우지속시간과 영양염류 유출 부하량은 양의 상관관계(R>0.6)를 나타내어 팔당호의 부영양화 문제를 관리하기 위해 개인하수처리지역에 대한 우선적 정책이 필요함을 알 수 있다.
Non-point source (
In Korea, more than 70% of annual rainfall occur during the summer monsoon period. Consequently, reservoirs have been created for water management and > 90% of Korean water supplies use surface water from rivers and reservoirs (Park et al., 2009). The Paldang reservoir plays an important role in supplying drinking water to Seoul (the capital of South Korea) and the surrounding regions. It includes several multi-purpose dams which control the hydrological and water quality characteristics of the river system. High intensity rainfalls have been occurring frequently causing high fluctuations in total effluent load in Paldang reservoir. Water quality degradation, particularly eutrophication issues in the Paldang reservoir over the last few decades has been continually reported (Kim et al., 1995; Shin et al., 2000; Youn et al., 2010) and stormwater runoff from various areas such as urban, agricultural, and industrial regions is considered to be a major source of water quality degradation.
While managing stormwater runoff, the land use of a catchment area plays an important role in the runoff process. Land use types can dictate or correlate with many other factors such as ground cover, soil type, topography and even rainfall patterns when looking at a much larger scale. Several researchers have shown that there are strong relationships between the land use of a particular site and the runoff volume and characteristics (Ying et al., 2009). In this study stormwater runoff was monitored and characterized from seven different counties within Paldang watershed, according to land use and population density. Several monitoring sites were selected within each county based on sewer system as some areas within each county is connected to the public sewer system while others have individual or no sewer system.
The primary purpose of this study was to characterize the stormwater runoff according to land use type and sewer system facility in Paldang watershed. All sites were grouped into two groups; those connected to the public sewer system (referred as
The Paldang reservoir is one of Korea’s major reservoirs, and one from which most people in Seoul and the surrounding areas receive drinking water. The watershed of Paldang reservoir covers 20,459 km2 comprising the portion of 3 provinces, 11 cities and 18 counties. Monitoring sites were selected evenly at 7 special countermeasure counties, according to land-use and population density. A total of 76 monitoring sites were selected within 7 counties in Paldang watershed (Figure 1). Geographic information system (
[Table 1.] Summary statistics of rainfall and land use type in study area
Summary statistics of rainfall and land use type in study area
2.2. Sampling Strategy and Water Quality Parameters Analysis
Pollutant concentrations, rainfall, and flow were measured for the entire storm duration. Among the 76 sites selected for storm water monitoring in Paldang watershed, 48 were connected to the public sewer system (
Some stormwater management strategies are based on the assumption that there is a first flush of pollutants at the start of each event. The first flush of pollutants can be visualized by a hydro-pollutograph, in which an X-Y plot of pollutant mass (M) against volume (V) is developed. On this plot a cumulative M-V line and a bisector line (45° line) are drawn and first flush occurred when M-V line lies above the bisector line. In this study first flush mass and volume is calculated by the difference of M-V line and bisector line. The highest difference point between M-V and bisector line means the first flush amount for
Similarly
Where
The runoff coefficients could be calculated for the storm event measured by taking into account the total rainfall and total catchment area and is an important factor in calculating the pollutant load. The generated load mechanism of watershed development was estimated by using the
3.1. Rainfall and Land Use Characteristics of Monitoring Sites
The statistical summary of monitored rainfall events and land use percentage is shown in table 1. The study area is classified into four different land use types including impervious cover, farm land, paddy field, and forest. The geomorphological factors like slope and population density were also quantified. At
Initial rainwater interception is one of the effective and popular measure to reduce runoff pollutant loads if the catchments have high first flush intensity. Generally, the first flush intensifies as the watershed area gets smaller, the impervious land area gets larger or the rainfall intensity increases (Lee and Bang, 2000). A Similar trend was observed in this study for most water quality parameters. The first flush intensity for
[Table 2.] Correlation of EMCs and pollutant loads with various parameters
Correlation of EMCs and pollutant loads with various parameters
3.3. Pollutant Loads and EMCs Comparison
The runoff coefficient calculated for
However, the pollutant loads results were different compared to
3.4. Correlation of EMCs and Pollutant Loads with Different Parameters
The Pearson correlation analysis was carried out in order to determine the relationship of
This study focused on characterizing stormwater runoff from the Paldang watershed area based on land-use type and sewer system coverage. In recent years the water quality degradation, especially eutrophication problem in Paldang reservoir is extensively reported. The major sources of excessive nutrients and eutrophication are fertilizers and animal manure, mostly received from agricultural non-point sources. It was found that monitoring sites with a higher percentage of forest land-use with no or individual sewer system coverage generates higher pollutant concentrations for particulate matter and nutrients. Lack of sewer system within these sites accelerates the erosion of topsoil and the untreated stormwater runoff is constantly being discharged into the tributaries and subsequently entering the reservoir without any treatment. Based on first flush analysis, it was proposed that installation of the runoff interception system for the first 43 % of storm runoff can capture up to 59 % of nutrient load within these sites and contribute meaningfully in combating eutrophication problem in Paldang reservoir. On the contrary, the sites connected to public sewer network with higher impervious land-use generates higher pollutant concentrations for organic matter. The results of this study will be helpful for